Environmental biology of fishes, tập 93, số 1, 2012

Environ Biol Fish (2012) 93:1–12
DOI 10.1007/s10641-011-9881-4

Feeding ecology and prey preferences of a piscivorous fish
in the Lagoa do Peixe National Park, a Biosphere Reserve
in Southern Brazil
Fabiano Corrêa & Marlucy Coelho Claudino &
Rodrigo Ferreira Bastos & Sônia Huckembeck &
Alexandre Miranda Garcia

Received: 17 June 2010 / Accepted: 27 June 2011 / Published online: 13 July 2011
# Springer Science+Business Media B.V. 2011

Abstract We investigated the diet, feeding strategy,
size-related dietary shifts and prey preferences of
South American Hoplias aff. malabaricus in an
internationally recognized but poorly investigated
Biosphere Reserve in southern Brazil. Fish were
caught between April 2008 and March 2009 using a
variety of fishing gear. The analysis of 113 individuals
revealed a diet essentially composed of fish (16
species), particularly characid species (9). The diet
became more diverse and contained larger fish prey
with increasing predator size. Feeding strategy analysis revealed a clear specialization towards the
consumption of fish. However, individuals did not
prey upon particular prey species, instead opportunistically consuming many different fish species, which
could be a strategy to avoid intraspecific competition.
Characid species were the most important prey,
followed by poecillids. A multi-gear sampling of the
ichthyofauna revealed that these prey species were the

most abundant (Characidae: 61.3%, Poeciliidae
18.8%) of the 14 fish families occurring at the study
site, suggesting that the predator exploits the most
abundant fish resources available rather than the rarer
F. Corrêa (*) : M. C. Claudino : R. F. Bastos :
S. Huckembeck : A. M. Garcia (*)
Instituto de Oceanografia, Laboratório de Ictiologia,
Universidade Federal de Rio Grande,
Campus Carreiros, Caixa Postal 474, CEP 96.201-900 Rio
Grande, RS, Brazil
e-mail:
e-mail:

fish prey. These findings suggest that potential topdown controls exerted by H. aff. malabaricus in this
system follow specific food web pathways that seem
to be mediated by the abundance of prey resources.
Keywords Diet . Feeding strategy . Size-related dietary
shift . Trahira . Food niche . Characins

Introduction
Piscivorous fish play an important role in the array of
ecosystem services provided by ichthyofauna due to their
regulation of prey populations and, therefore, their impact
on trophic cascades (Helfman et al. 2009). Such
influences can have crucial effects on the functioning
of aquatic ecosystems and the levels of biodiversity they
sustain (Polis and Winemiller 1996; Mazzeo et al.
2010). Temporal variations in predator abundance have
a profound impact on not only the abundance of aquatic
prey but also on adjacent terrestrial ecosystems via

indirect interactions with terrestrial consumers (Hebert et
al. 2008). Studying the feeding ecology of piscivorous
fish is, therefore, a key step towards understanding the
processes driving biodiversity in aquatic ecosystems.
Such knowledge is critically relevant in conservation
areas to guide managers and decision makers to cope
with anthropogenic impacts, such as when exotic
species threaten native ones (Zaret and Paine 1973).
Lagoa do Peixe National Park (LPNP) is a poorly
investigated conservation area in the coastal plain of


2

southern Brazil which harbors many diverse and
productive aquatic fauna, including endangered fish
species such as the annual fish Austrolebias minuano
(Corrêa et al. 2009). It was recognized as a Ramsar
Site and a UNESCO Biosphere Reserve in 1993,
largely due to its important ecological role as a
stopover site for migratory shorebirds in South
America (Tagliani 1995). Despite the importance of
the LPNP importance for conservation, no prior
information on fish trophic ecology or aquatic food
web structure is available for this unique ecosystem.
The most abundant piscivorous fish in the freshwater wetlands of the LPNP is the South American
Hoplias aff. malabaricus (Bloch, 1794) (Loebmann
and Vieira 2005). This perch-like piscivore of the
Erythrinidae family is distributed from Costa Rica
(Central America) to Southern South America

(Argentina) and is well known for having a strong
top-down structuring role on trophic food webs of
lentic aquatic systems (Winemiller 1989; Mazzeo et
al. 2010). Although it is well adapted to lentic
environments, it is also found in small and large
rivers, especially in pools with abundant marginal
vegetation. It is cryptically colored and captures its
prey by ambush and is active mainly at night
(Loureiro and Hahn 1996). It is considered a top
predator with trophic levels ranging from 2.4 to 4
(Garcia et al. 2006; Rodríguez-Graña et al. 2008).
Mesocosm experiments revealed that H. aff.
malabaricus can exert a strong control on planktivorous fish with cascading effects on chlorophyll a,
water turbidity and zooplankton abundance (Mazzeo
et al. 2010). These authors recommended, however,
that additional studies be carried out in whole-lake
systems because the simplified conditions and small
scale of mesocosm experiments hinder direct extrapolation. Also, the high complexity of the food web
and spatial heterogeneity of natural aquatic systems in
subtropical and tropical regions represent additional
constraints and should be investigated. However, prior
studies on the diet and feeding behavior of H. aff.
malabaricus have been restricted to streams and river
flood plains, with no known studies on subtropical
freshwater wetlands. For example, field studies conducted on streams and river flood plains have shown
that small fish usually comprise the main prey of H.
aff. malabaricus, although invertebrates, especially
insects, vegetation remains and organic detritus can
also be found in the stomach contents of H. aff.

Environ Biol Fish (2012) 93:1–12

malabaricus (Loureiro and Hahn 1996; Carvalho et
al. 2002; Peretti and Andrian 2008; Corrêa and
Piedras 2009). Size-related diet shifts also occur, with
small juveniles feeding primarily on invertebrates,
while subadults and adults are piscivorous (Winemiller
1989). However, these prior studies did not unambiguously show the fish prey preferences of the H. aff.
malabaricus under natural conditions because the
authors did not carry out a concomitant evaluation of
fish prey availability in the study site.
Considering the crucial role that H. aff. malabaricus can have on aquatic food webs and the lack of
information about its feeding ecology on subtropical
wetlands, the present study investigates its diet,
feeding strategy and size-related dietary shifts in a
wetland located within an important conservation area
in southern Brazil. Also, based on a concomitant
multi-gear sampling of the ichthyofauna in the study
site, our work reveals the prey preferences of this top
predator under natural field conditions.

Material and methods
Study area
The LPNP was created in 1986 to protect crucial
feeding and resting sites for migratory birds along the
coast of Rio Grande do Sul state in southern Brazil
(Fig. 1). The LPNP has a humid subtropical climate,
with mean temperatures ranging from 14.6°C in
winter to 22.2°C in summer, and a mean annual
temperature of 17.5°C. The annual precipitation

ranges from 1150 to 1450 mm yr−1, with an annual
mean of 1250 mm yr−1 (Tagliani 1995). The main
lagoon (locally known as ‘Lagoa do Peixe’) consists
primarily of shallow areas (<50 cm), except in its
channel and at its communication with the Atlantic
Ocean in its central portion where it can reach a depth
of 2 m (Loebmann and Vieira 2005). The connection
of the lagoon with the sea often remains closed for
several months each year until excess freshwater,
usually from rainfall during winter months, leads to
the opening of the mouth of the estuary and the reestablishment of its connection with the sea. In some
years, the mouth of the estuary is artificially opened
with the use of machinery to promote the entrance of
larvae and juvenile shrimps and fish into the lagoon
(Loebmann and Vieira 2005).


Environ Biol Fish (2012) 93:1–12

3

Fig. 1 Southern Brazil (a)
and the location of the
Lagoa do Peixe National
Park (LPNP) (dashed line)
in the coastal plain (b) with
the position of the freshwater wetland in the northern
reaches of the park where
specimens of the Hoplias
aff. malabaricus were captured (closed circle)

The study site is located on a coastal plain with
low topography (< 20 m.a.s.l.) (Rambo 2000) under
strong influence of rainfall anomalies associated with
the El Niño Southern Oscillation phenomena (Grimm
et al. 1998), which cause higher and lower than
average rainfall in this region during the El Niño and
La Niña episodes, respectively. These rainfall anomalies trigger hydrological changes and can have
profound effects on estuarine (Garcia et al. 2001)
and freshwater fish assemblages in southern Brazil
(Garcia et al. 2003).
Field collections, laboratory procedures and data
analysis
Specimens were obtained during a fish community
survey conducted monthly from April 2008 to May
2009 in a freshwater wetland located in the
northern reaches (31°65′10″S, 50°51′271″ W) of
the LPNP (Fig. 1). In general, the physical features

were similar to those found on other permanent
wetlands occurring in the northern and southern
reaches of the park (Loebmann and Vieira 2005) and
in nearby areas (Maltchik et al. 2010). Individuals
were caught using multiple types of fishing gear,
including gillnets, beach seines and beam trawls.
Two gillnet sets (4×2 m) with mesh sizes of 15, 20,
30 and 35 mm were employed from late afternoon
until dawn in deeper waters (1.5–2.0 m) in order to
catch larger individuals (>200 mm). During the
afternoon (from 1400 to 1700), one to two beach

seine (9 m long, 2.4 m high, mesh size 13 mm wings
and 5 mm center) hauls were conducted in the open
margins of the wetland, and three beam trawl (mouth
of 1×1 m and size mesh of 5 mm) hauls were
employed in the vegetated margins of the wetland in
each field trip. The hauls conducted in the shallower
waters (< 1.5 m) targeted mainly smaller individuals
(< 200 mm). Some cryptic species were caught by
dip net, which was used for approximately 15 min in


4

each field collection. Aside from H. aff. malabaricus
specimens, all fish species collected in the freshwater wetland using the previously mentioned types of
fishing gear had their total size and numerical
abundance recorded in order to assess the general
relative abundance patterns of the ichthyofauna at
the study site. Such concomitant surveys of the
abundance of the piscivorous fish and its fish prey
populations were used to infer prey availability and
patterns of resource exploitation by the H. aff.
malabaricus population.
Immediately after their collection, individuals
were euthanized and placed on ice. Later, they
were transported to the laboratory and stored in a
freezer. After thawing, each individual was weighed
(Wt, g) and measured (total length, TL, mm) and,
after being surgically dissected, had their stomach
contents analyzed. Food items were weighed on an

analytical balance with an accuracy of 0.0001 g.
Food items found in the stomachs were identified
to the lowest possible taxonomic level using a
stereoscopic microscope. When a food item was
intact, its weight (g) and total length (TL, mm)
were measured.
Food resources found in non-empty stomachs were
quantified using the following parameters (Hyslop
1980): a) frequency of occurrence (%F), which
represented the percentage of the total number of
stomachs in which a particular food item was found,
b) numerical abundance (%N), which represented the
abundance in the percentage of a food item in relation
to the total abundance of all stomachs c) weight (%W)
of the item, which represented the weight (g) in
percentage of a food item in relation to the total
weight of all stomachs. These parameters (%F,%N,%
W) were combined into the Index of Relative
Importance of Pinkas et al. (1971) with the following
formula: IRI ¼ %F»ð%N þ %WÞ, which was computed for each food item.
In order to assess the influence of hydrological
changes in the study area, we analyzed diet and
feeding ecology during periods of lower and higher
precipitation. In order to accomplish this, monthly
mean values of rainfall (square root transformed)
were analyzed with the Bray-Curtis similarity index in
order to distinguish temporal rainfall patterns during
the studied period. Data were obtained in two
meteorological stations located in cities (Rio Grande
and Mostardas) near the study area (Fig. 1). Differ-

Environ Biol Fish (2012) 93:1–12

ences in diet composition between rainfall periods
revealed by the cluster analysis were evaluated by
MDS (Multi-Dimensional Scaling) and ANOSIM
analyses using the Primer software package (Clarke
and Gorley 2006).
The feeding strategy of H. aff. malabaricus and
the characteristics of their food niche were evaluated
by the graphical method proposed by Amundsen et
al. (1996). In this approach, prey-specific abundance
is defined as the percentage a prey taxon comprises
of all prey items in only those predators in which the
actual prey occurs according to the formula Pi =(∑Si/
∑Sti) x 100, where Pi is the prey-specific abundance
of prey i, Si the stomach content (weight) comprised
of prey i, and Sti the total stomach content in only
those predators with prey i in their stomach
(Amundsen et al. 1996). In the resulting diagram,%
F values are arranged in the x-axis and Pi values on
the y-axis. The feeding strategy (generalist-specialist
dichotomy) and the contribution of each individual
to the food niche structure is obtained by analyzing
the distribution of points (each one representing a
food item) along a graph. The population as a whole
can be considered a specialist when the prey points
are positioned at the top right of the graph, whereas
their placement in the bottom half of the graph
suggests a population with a generalist feeding

behavior. When points are located in the upper left
corner of the diagram (i.e., with low%F and high Pi)
they indicate individual opportunistic or specialist
feeding behavior of some individuals within the
predator population.
The relationship between the weight (g) and total
length (TL, mm) of fish prey consumed and the total
length (TL, mm) of the predator was evaluated with a
nonlinear regression. In the model calculation (PreyTL =
a * exp b * PredatorTL), the algorithm of GaussNewton was used based on an iterative process using a
convergence criterion of 1.0−6 and baseline values
(‘seeds’) for the regression constant (a) and the
regression coefficient (b) of 1 and 0.01, respectively
(Haimovici and Velasco 2000; Cantanhêde et al. 2009).
Size-related dietary shifts were also analyzed based on
three size classes: 0–100, 101–200 and 201–350 mm
TL, with 16, 20 and 18 individuals in each one,
respectively. Differences in the average total weight (g)
of the food found in the stomach content of these three
size classes were evaluated by the Kruskal-Wallis test
(Zar 1994).


Environ Biol Fish (2012) 93:1–12

Results
Seasonal changes in rainfall
Rainfall showed strong variation across months, with
values ranging from 12.4 mm in November 2008 to
129.15 mm in August 2008. In general, the average

rainfall was higher during the winter and summer
(70.9 and 80.7 mm, respectively) than in the spring
and autumn (19.9 and 38.3 mm, respectively). Cluster
analysis applied to monthly rainfall values revealed
(at 75% of similarity) two main groups (Fig. 2a). The
former were comprised of months with low precipitation (< 25 mm), whereas the later by months with
moderate to high (25–100 mm) values (Fig. 2b).
Diet composition and seasonal changes
A total of 113 individuals with sizes (TL) ranging
from 26 to 364 mm had their stomach contents
Fig. 2 Dendogram showing
the similarity (Bray-Curtis
index) among mean values
of rainfall (square root
transformed) in each month
from April 2008 to March
2009. Data obtained from
two meteorological stations
located in the cities of Rio
Grande and Mostardas (see
map on Fig. 1). The horizontal line denotes similarity at 75% (a). Mean values
of rainfall during the low
and moderate-high periods
obtained in the cluster
analysis (b)

5

analyzed, and nearly half of them (52.1%) were
empty. The analysis of the food content of the nonempty stomachs revealed 20 items (Table 1). Fish

were the most conspicuous items in the diet of H. aff.
malabaricus and included 15 species belonging to 6
distinct fish families. Fragments of insects and plants
were also found in the stomach contents, but they had
comparatively lower contributions in terms of numerical abundance (%N) and biomass (%W) (Table 1).
Characins were the most frequent and abundant
prey found in the diet, with Cheirodon interruptus
being the fish prey with the highest numerical
abundance. The spotted livebearer Phalloceros caudimaculatus (Poeciliidae) was the second most
numerous fish in the diet of H. aff. malabaricus.
The numerical abundance patterns of these two main
fish prey (characins and poecilids) matched the
relative abundance of the two most abundant fish
families at the study site closely. The multi-gear
sampling of the ichthyofauna revealed that Characi-


6
Table 1 Frequency of
occurrence (%F), numerical
abundance (%N), weight
(%W) and index of relative
importance (%IRI) of the
food items found in the
stomach content of Hoplias
aff. malabaricus in the
‘Lagoa do Peixe’ National
Park (LPNP), southern
Brazil

Environ Biol Fish (2012) 93:1–12
Food items

Code

%Fo

%N

%W

IRI%

Actinopterygii
Characiformes
Characidae
Astyanax eigenmanniorum (Cope, 1894)

Asteig

1.85

0.95

0.77

0.08

Astyanax jacuhiensis (Cope, 1894)

Astjac

3.7

1.9

4.07

0.58

Astyanax sp.

Astspp

7.41

4.76

3.26

1.56

Characins not identified

Charac

12.96

7.62

3.45

3.78

Cheirodon interruptus (Jenyns, 1842)

Cheint

11.11

9.52

1.97

3.37

Hyphessobrycon bifasciatus Ellis, 1911

Hypbif

1.85

0.95

0.8

0.09

Hyphessobrycon luetkenii (Boulenger, 1887)

Hyplue

1.85

1.9

Hyphessobrycon sp.

Hypspp

1.85

1.9

Pseudocorynopoma doriae Perugia, 1891

Psedor

1.85

0.95

0.95
1,00
0.11

0.14
0.14
0.05

Erythrinidae
Hoplias aff. malabaricus (Bloch, 1794)

Hopmal

1.85

0.95

0.55

0.07

Siluriformes
Heptapteridae
Heptapterus sympterygium Buckup, 1988

Hepsyp

1.85

0.95

1.53

Pimelodella australis Eigenmann, 1917

Pimaus

3.7

1.9

2.17

0.12
0.40

Rhamdia quelen (Quoy & Gaimard, 1824)

Ranque

1.85

0.95

30.07

1.52

Phacau

12.96

6.67

0.57

2.48

Cynmel

1.85

0.95

0.11

0.05

Ausfac

1.85

0.95

10.18

0.54

Cyprinodontiformes
Poeciliidae
Phalloceros caudimaculatus (Hensel, 1868)
Cyprinodontiformes
Rivulidae
Cynopoecilus melanotaenia (Regan, 1912)
Perciformes
Cichlidae
Australoheros facetus (Jenyns, 1842)
Others

Organic matter

Orgmat

Plant remains not identified

Plant

9.26

4.76

0.53

20.37

22.86

0.93

1.29
12.8

Insect remains not identified

Resins

5.56

2.86

0.03

0.42

Fishes remains not identified

Resfis

42.59

25.71

36.96

70.49

dae (61.3%) and Poeciliidae (18.8%) were the most
abundant of the 14 fish families occurring at the
study site (Fig. 3). Other fish prey found in the diet
belonged to the Heptapteridae and Cichlidae families. In contrast, these families were more important
in terms of their %W than their %N contribution
(Table 1). Accordingly, these prey were not abundant
in the study site but were characterized by their
greater sizes (especially cichlids), when compared to
characins and poecillids (Fig. 3). The other eight fish
families that occurred in small proportions (< 5%) at

the study site were not found in the diet of H. aff.
malabaricus (Table 1).

No differences were observed in the diet composition of individuals caught during low and
moderate-high rainfall periods (Fig. 4). This pattern
was corroborated by the ANOSIM, which did not
reveal statistically significant differences between
the periods (Global R=0.49, p=−0.006). Therefore,
we pooled our dataset for the subsequent data
analysis on feeding strategy and size-related dietary
shifts.


Environ Biol Fish (2012) 93:1–12

7

Feeding strategy and size related dietary shift
The feeding strategy analysis revealed that, as a
whole, the studied population had a specialist feeding
strategy towards the consumption of fish (Fig. 5a),
resulting in a narrow niche width as depicted by the
box inserted in Fig. 5a. However, when the feeding
strategy was analyzed considering only fish prey,

Fig. 3 a Numerical abundance (%) and number of species in
each family (parentheses) and b average total length (TL, mm)
of fish species in the study site based on a multi-gear survey
conducted concomitantly with the collection of the species
studied here (Hoplias aff. malabaricus)

Fig. 4 MDS ordination of the composition of the diet of
Hoplias aff. malabaricus during periods of low (L) and

moderate-high (M-H) rainfall periods. Data values were
square-root transformed, and the Bray-Curtis similarity was
used

Fig. 5 Feeding strategy diagram for individuals of the Hoplias
aff. malabaricus in the Lagoa do Peixe National Park with fish
prey pooled as a single food category (a) or separately by
species (b). Prey-specific abundance (Pi) is plotted against
frequency of occurrence (%F) of food items in the diet of
Hoplias aff. malabaricus. The inserted box represents a
conceptual diagram of a resource niche width characterized by
a high between-phenotype component (sensu Amundsen et al.
1996) to the niche width contribution. The following food items
were considered: Heptapterus sympterygium (Hepsyp), Cynopoecilus melanotaenia (Cynmel), Hoplias aff. malabaricus
(Hopmal), Rhamdia quelen (Ranque), organic matter (OrgMat),
fish remains (FisRem), Phalloceros caudimaculatus (Phacau),
Astyanax jacuhiensis (Astjac), Cheirodon interruptus (Cheint),
Astyanax spp. (Astspp), Pimelodella australis (Pimaus), Characidae (Charac), Plant fragments (Plant), Insects (Insect)


8

there was a high variability in prey consumption
between individuals (phenotypes). Some individuals
preyed upon certain fish prey, such as the catfishes
Heptapterus sympterygium and Rhamdia quelen, the
annual fish Cynopoecilus melanotaenia and juveniles
of the H. aff. malabaricus, resulting in low frequency
of occurrence (%F) and higher prey-specific abundance values (Pi) in the diagram (Fig. 5b). This
pattern revealed a higher between-phenotype component to the niche width of the studied species and,

consequently, greater partitioning of the food resources (mainly fish) between individuals of the predator
population, as depicted by the box inserted in Fig. 5b.
There were conspicuous size-related dietary shifts
in terms of diet composition and prey sizes consumed
by H. aff. malabaricus; with increasing predator size,
the diet became more diverse (Table 2, Fig. 6) and
comprised larger fish prey (Fig. 7). There was a
significant increase in prey diet richness with the
increase in size (TL, mm) (Kruskal-Wallis, H: 6.61,
df: 2, p<0.037) (Fig. 6) that was related to an increase
in the consumption of characid species by larger
individuals (Table 2). There was also a significant
positive correlation between prey (mm TL) and
predator sizes (mm, TL) (p<0.00) (Fig. 7), which
was mainly associated with the consumption of larger
prey, such as the freshwater catfishes Pimelodella
australis (average size: 41.5 mm TL) and Rhamdia
quelen (138.0 mm TL) and the cichlid Australoheros
facetus (73.5 mm TL), by larger individuals (201–
350 mm TL) (Table 3).
The tendency to consume larger prey was also
observed in the consumption of characins. Altogether
with the consumption of smaller characins like
Cheirodon interruptus (27.7 mm) and Astyanax sp.
(28.5 mm), larger specimens (201–350 mm TL)
included in their diet larger characins such as
Astyanax eigenmanniorum (42.0 mm), A. jacuhiensis
(48.5 mm), Hyphessobrycon luetkenii (39.5 mm), H.
bifasciatus 39.0 mm) and Hyphessobrycon sp.
(34.5 mm), which were absent in the diet of smaller

H. aff. malabaricus specimens (< 200 mm TL)
(Table 3).

Discussion
Our results revealed that H. aff. malabaricus, in this
subtropical wetland, has a carnivorous feeding mode

Environ Biol Fish (2012) 93:1–12

focused primarily on fish. Among fish prey, characins
were the dominant group followed by poeciliids. The
predominance of characins in the H. aff. malabaricus
diet has been described by earlier studies with the
species (Winemiller 1989; Bistoni Mlos et al. 1995;
Loureiro and Hahn 1996; Corrêa and Piedras 2009).
For example, Loureiro and Hahn (1996) showed that
characins were the main food of this species in the
Segredo reservoir (South Brazil), and a similar
finding was reported by Carvalho et al. (2002) for a
population inhabiting the Vermelho River in Pantanal
(Central Brazil). These studies, however, did not
mention whether diet composition was related to
resource availability. The concomitant sampling of the
ichthyofauna at the current study site showed that H.
aff. malabaricus seems to exploit the most abundant
fish resources available. The two most abundant fish
families in the study site (Characidae and Poeciliidae)
were clearly the most frequent and abundant in the
diet of H. aff. malabaricus. Conversely, most of the
least abundant (<1%) fish families at the study site,

such as Sternopygidae, Gymnotidae, Hypopomidae,
Crenuchidae, Synbranchidae, Anablepidae, were not
found in the diet of H. aff. malabaricus. This suggests
that this species exploits the most abundant fish
resources available rather than rare fish prey. Habitat
use by both predator and prey also helps explain the
higher predation on Characidae and Poeciliidae
species. Hoplias aff. malabaricus is strongly associated with habitats highly structured by riparian forest
or aquatic plants (Luz-Agostinho et al. 2008), where
small fish such as characins and poecillids usually
seek refuge from predators (Petry et al. 2003; Pelicice
and Agostinho 2006). Such habitat seems to favor
ambush predators such as the species studied here
(Almeida et al. 1997, Luz-Agostinho et al. 2008).
Although moderately abundant (~5%), the Callichthydae (Callichthys callichthys) and Curimatidae
(Cyphocharax voga) families were also absent in the
H. aff. malabaricus diet. In contrast with Characidae
and Poeciliidae specimens that are typically found
feeding in the water column (Ceneviva-Bastos and
Casatti 2007; Abilhoa et al. 2008), specimens of
Callichthydae and Curimatidae found in the study site
were bottom dwellers typically feeding on detritus
near the substrate (Corrêa and Piedras 2008). Based
on their absence in the stomach content of H. aff.
malabaricus, we speculate that H. aff. malabaricus
shows preference (or higher capture success rate) for


Environ Biol Fish (2012) 93:1–12

9

Table 2 Frequency of occurrence (%F), numerical abundance
(%N), weight (%W) and index of relative importance (%IRI) of
the food items found in the stomach content of three size
Food items

n=16 (0–100)
%F

%N

classes (0–100 mm TL, 101–200 mm TL, 201–300 mm TL) of
the Hoplias aff. malabaricus in the ‘Lagoa do Peixe’ National
Park (LPNP), southern Brazil. n=number of individuals
n=20 (101–200)

%W

IRI%

%F

%N

n=18 (201–350)

%W

IRI%

%F

%N

%W

IRI%

Actinopterygii
Characiformes
Characidae
Astyanax eigenmanniorum
Astyanax jacuhiensis
Astyanax sp.

5.56

2.04

11.11

4.08

0.91
4,82

0.36
2.18

10.00

5.56

1.47

1.08

11.11

6.12

3.64

Characins not identified

6.25

5.00

22.84

6.64

20.00

13.89

19.30

10.21

11.11

4.08

0.44

1.11

Cheirodon interruptus

6.25

5.00

0.75

1.37

15.00

11.11

10.57

5.05

11.11

10.20

0.72

2.68

Hyphessobrycon bifasciatus

5.56

2.04

0.94

0.37

Hyphessobrycon luetkenii

5.56

4.08

1.13

0.64

Hyphessobrycon sp.

5.56

4.08

1.18

0.64

5.56

2.04

0.65

0.33

5.56

2.04

1.18

0.39

5.56

2.04

35.54

4.60

5.56

2.04

12.03

1.72

Pseudocorynopoma doriae

5.00

2.78

0,91

2.39

0.28

Erythrinidae
Hoplias aff. malabaricus
Siluriformes
Heptapteridae
Heptapterus sympterygium

6.25

5.00

51.91

13.57

Pimelodella australis

5.00

2.78

9.40

0.94

Rhamdia quelen
Cyprinodontiformes
Poeciliidae
Phalloceros caudimaculatus

25.00

20.00

11.33

29.88

6.25

5.00

3.62

2.06

15.00

8.33

1.90

2.36

Cyprinodontiformes
Rivulidae
Cynopoecilus melanotaenia
Perciformes
Cichlidae
Australoheros facetus
Others
Organic matter

12.50

10.00

1.21

5.34

5.00

2.78

Plant remains not identified

12.50

20.00

0.06

9.57

10.00

11.11

Insect remains not identified

12.50

10.00

0.40

4.96

5.00

2.78

0.13

0.22

Fishes remains not identified

25.00

20.00

7.90

26.61

55.00

38.89

52.66

77.41

fish prey foraging in the water column, like the
Characidae and Poecilidae species, rather than bottom
dweller species.
The analysis of the feeding strategy of the H. aff.
malabaricus population revealed a clear specialization
towards the consumption of fish when considering

only major food categories. However, when the feeding

3.49

0.21

11.11

4.08

0.59

1.14

2.25

38.89

32.65

0.58

28.50

44.44

18.37

35.67

52.95

strategy was analyzed focusing on only the food
category ‘fish’, the analysis showed that individuals
did not prey upon a particular fish species, but, rather,
had a high degree of opportunism in the consumption
of different fish species. This pattern could arise from
the fact that the H. aff. malabaricus is a typical ambush
(sit-and-wait) predator preying upon prey species


10

Environ Biol Fish (2012) 93:1–12
Table 3 Average values of weight (W, g), total length (mm TL)
and total width (mm TW) of the food items found in the
stomach content of Hoplias aff. malabaricus in the ‘Lagoa do
Peixe’ National Park (LPNP), southern Brazil
Food items

Wt (g)

TL (mm)

Astyanax eigenmanniorum

0.5

42.0

Astyanax jacuhiensis

1.4

48.5

Astyanax sp.

0.3

28.5

Characins not identified

0.4

24.5

Cheirodon interruptus

0.2

27.7

Hyphessobrycon bifasciatus

0.5

39.0

Hyphessobrycon luetkenii

0.8

39.5

Hyphessobrycon sp.

0.5

34.5

Pseudocorynopoma doriae

0.1

21.0

0.4

27.0

1.0

56.0

Actinopterygii
Characiformes
Characidae

Fig. 6 Average number (+%95 C.I.) of different food items
(diet richness) found in the stomach content of three size
classes (0–100 mm TL, 101–200 mm TL, 201–350 mm TL) of
Hoplias aff. malabaricus in the Lagoa do Peixe National Park

entering its striking zone (Winemiller 1989), with no
particular specialization for a particular fish species.
This opportunistic feeding behavior has been previously observed in this species by other authors
(Cassemiro et al. 2005; Novakowski et al. 2007).
In a broader context, the generalist-specialist
dichotomy and the food-niche structure can be
considered in terms of between- and withinphenotype (individual) contributions. For instance, a
population with a generalist feeding strategy could
have a trophic niche with a high between-phenotype
component, when the individuals are preying upon
different resources, or a high within-phenotype
component, when most of the individuals are con-

Erythrinidae
Hoplias aff. malabaricus
Siluriformes
Heptapteridae
Heptapterus sympterygium
Pimelodella australis
Rhamdia quelen

0.7

41.5

20.2

138.0

Cyprinodontiformes
Poeciliidae
Phalloceros caudimaculatus

0.05

12.8

0.1

22.0

6.8

73.5

Cyprinodontiformes
Rivulidae
Cynopoecilus melanotaenia
Perciformes
Cichlidae
Australoheros facetus

Fig. 7 Relationship between total length (TL, mm) of the fish
prey and the predator, based on the fish species found in the
stomach contents of Hoplias aff. malabaricus in the Lagoa do

Peixe National Park. n=39

suming the same prey species (Amundsen et al.
1996). Bolnick et al. (2003) have argued that
between-phenotype variation in diet and resource
use patterns are more widespread among animal
populations than previously supposed. Future research
is needed to evaluate if the observed high degree of
individual-level food niche variation in H. aff. malabaricus is an outcome of its ambush feeding strategy and
its potential role in avoiding conspecific competition.
The analysis of the stomach contents of the studied
species revealed a clear size-related dietary shift
between diet composition and richness and the size


Environ Biol Fish (2012) 93:1–12

of the prey consumed. Dietary shifts have been
observed in H. aff. malabaricus populations occurring
in the Llanos Venezuelanos, with juveniles preying
upon insects and shifting to fish as they develop into
adults (Winemiller 1989). A similar decrease in the
importance of insects with increasing predator size
was also observed in the present study. However, the
present study also revealed a positive relationship
between sizes of both the fish prey and the predator.
Larger individuals (> 200 mm TL) had a richer diet
comprised of larger fish prey such as freshwater
catfishes and cichlids when compared with smaller (<
200 mm TL) H. aff. malabaricus specimens that

preyed mainly on smaller characins and poeciliids.
The consumption of these larger prey species could be
related to greater efficiency in capturing larger and
more mobile prey and could compensate for the
greater energy demands of adult individuals that need
to perform activities such as spawning, nest construction and egg guarding (Prado et al. 2006). Alternatively, this trend could be explained by changes in
mouth gape as the predator increases in size. Usually,
oral jaw dimensions and, in some cases, pharyngeal
gape are the primary determinants of the prey size
ranged consumed by predatory fishes (Helfman et al.
2009). For instance, Pusey et al. (2000) have shown
that interspecific and ontogenetic variation in diet are
strongly related to differences in body size and mouth
gape. In this case, we would expect that larger
individuals of H. aff. malabaricus would be able to
consume larger prey species regardless of their
nutritional status. Future studies are necessary to
evaluate the relative role of these hypotheses on
explaining the size-related dietary shift trend observed
for this species.
In conclusion, our findings show that the South
American subtropical wetland species, H. aff. malabaricus, preys mainly upon fish regardless of dry or
wet weather conditions and feeds opportunistically on
the most abundant prey species available. The
ubiquitous and smaller-sized (< 70 mm) characins
and poecillids, usually found in the water column near
or within riparian vegetation, constituted its main
prey, rather than the less abundant, and in most cases,
benthic species. Size-related dietary shifts occurred
and were characterized by the consumption of larger

prey such as catfish and cichlid species. These
findings suggest that fish predation exerted by H.
aff. malabaricus in this system follows specific food-

11

web pathways that seem to be mediated by the
abundance of prey resources. Additionally, the relationship between prey size and predator size adds a
layer of complexity to this picture. Future field
mesocosm or whole-system manipulative experiments, based on the insights provided by the current
work, should be carried out in order to assess the
strength of these food web pathways and their
potential effects on secondary production of subtropical wetlands harboring H. aff. malabaricus populations. Such information could provide a crucial
background in order to enhance ongoing conservation
plans for protecting this Biosphere Reserve from
increasing human activities in its vicinities such as
agriculture, fishery and the cultivation of exotic
species.
Acknowledgments We thank colleagues of the Ichthyology
Laboratory of the Oceanographic Institute of the Federal University of Rio Grande (FURG) for their assistance in the field,
especially Vinicius Condini; the Conselho Nacional de Desenvolvimento Científico e Tecnológico, CNPq (Grant No. 482920/
2007-6) and International Foundation of Science, IFS (Grant No.
A/4419-1) for providing financial support and the ICMBIO for
providing permit (14523-2 and 14523-4) for sample collections.

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Environ Biol Fish (2012) 93:13–21
DOI 10.1007/s10641-011-9885-0

The effects of intraspecific competition on the prey capture
behavior and kinematics of the bluegill sunfish,
Lepomis macrochirus
Janne A. Pfeiffenberger & Philip J. Motta

Received: 5 August 2010 / Accepted: 30 June 2011 / Published online: 27 July 2011
# Springer Science+Business Media B.V. 2011

Abstract Competition has broad effects on fish and
specifically the effects of competition on the prey
capture kinematics and behavior are important for the
assessment of future prey capture studies in bony
fishes. Prey capture kinematics and behavior in bony
fishes have been shown to be affected by temperature
and satiation. The densities at which bony fish are
kept have also been shown to affect their growth,
behavior, prey selection, feeding and physiology. We
investigated how density induced intraspecific competition for food affects the prey capture kinematics of
juvenile bluegill sunfish, Lepomis macrochirus. High
speed video was utilized to film five bold individuals
feeding at three different densities representing different levels of intraspecific competition. We hypothesized that: (1) the feeding kinematics will be faster at
higher levels of competition compared to lower levels
of competition, and (2) bluegill should shift from
more suction-based feeding towards more ram-based
J. A. Pfeiffenberger (*) : P. J. Motta
Department of Integrative Biology,
University of South Florida,
4202 E Fowler Avenue,
Tampa, FL 33620, USA
e-mail:
Present Address:
J. A. Pfeiffenberger
Department of Biological Sciences,
Florida Institute of Technology,
150 W University Boulevard,
Melbourne, FL 32901, USA

feeding with increasing levels of competition in order

to outcompete conspecifics for a prey item. We found
that, with increased intraspecific competition, prey
capture became faster, involving more rapid jaw
opening and therefore greater inertial suction, shorter
mouth closing times, and shorter gape cycles. Furthermore, the attack velocity of the fish increased with
increasing competition, however a shift towards
primarily ram based feeding was not confirmed. Our
study demonstrates that prey capture kinematics are
affected by the presence of conspecifics and future
studies need to consider the effects of competition on
prey capture kinematics.
Keywords Prey capture kinematics . Competition .
Bluegill . Density . Ram-suction

Introduction
Competition for food in fishes has been extensively
studied for decades (Werner and Hall 1979; Mittelbach
1981; Ehlinger 1990; Taborsky 1998) demonstrating
that fish compete for food resources by exploitation,
scramble and contest competition (Ward et al. 2006).
Consequently, to successfully compete for food,
rapid acquisition of the prey is crucial. Previous
research on the effects of fish density and size on
the feeding behavior of Pacific halibut Hippoglossus stenolepis, found that fish at higher densities
will locate and consume the prey in less time than


14

conspecifics at lower predator densities (Stoner and

Ottmar 2004). However, the effects of competition
on prey capture kinematics of fishes have not been
investigated.
Fishes can capture food by ram, suction, or biting,
or a combination of the three (Liem 1980; Norton and
Brainerd 1993). During prey capture, modulation of
prey capture kinematics of bony fishes occurs in
response to position, size and elusiveness of prey
(Nyberg 1971; Wainwright and Lauder 1986; Nemeth
1997a). Ram feeding involves high attack velocities
to overtake the prey item whereas suction feeding
involves lower attack velocities and precise positioning to suck the prey item into the mouth and usually a
combination of these two feeding modes is utilized by
fish (Nemeth 1997a, b; Higham 2007). With increasing intraspecific competition, we would expect predators, such as the bluegill sunfish Lepomis
macrochirus, to approach the prey at higher attack
velocities and to capture the prey without braking
before employing a more ram dominated prey
capture.
Bluegill sunfish, Lepomis macrochirus Rafinesque
1819 are native to and widespread in North America.
Bluegill sunfish are considered one of the highest
performing suction feeders (Carroll et al. 2004) and
have been the focus of extensive research in prey
capture kinematics and performance (Gillis and
Lauder 1995; Ferry-Graham et al. 2003; Higham et
al. 2005a; Higham et al. 2006; Holzman et al. 2008)
and feeding ecology (Werner 1977; Mittelbach 1981;
Osenberg et al. 1988; Savino et al. 1992; Brogowski
et al. 2005). Increased intraspecific competition for
food has been assumed to affect the growth of bluegill

living in high density populations (Wiener and
Hanneman 1982) which is further supported by the
general assumption that almost all conspecifics
compete for food and habitat since they occupy the
same niche (Ward et al. 2006).
Previous studies have shown that temperature
(Wintzer and Motta 2004; Devries et al. 2006),
satiation (Sass and Motta 2002), prey type (Norton
1991) and body size (Richard and Wainwright 1995)
can affect the prey capture kinematics of fishes, and
that higher stocking densities and competition reduce
the growth and survival rate of fishes (Houde 1977;
Anderson et al. 2002).
The goal of this study is to examine the effects of
intraspecific competition on the prey capture kine-

Environ Biol Fish (2012) 93:13–21

matics of bluegill sunfish. Specifically, it is hypothesized that: (1) bluegill sunfish will feed faster at
higher levels of competition compared to lower levels
of competition, and (2) bluegill sunfish will shift from
primarily suction feeding towards more ram feeding
with increasing levels of intraspecific competition.
This study will address whether future studies should
take into account the effects of competition on prey
capture kinematics.

Materials and methods
Study organism
Thirty five juvenile bluegill sunfish (8.9–10.0 cm

SL) were caught by cast netting from the Hillsborough River drainage in Hillsborough County,
Florida, USA. The animals were housed in 40-liter
aquaria individually at 22°C with a 12:12 light
period and were acclimated for 2–4 weeks. The
tanks were screened on the sides and the back with
white paper such that the animals could not see each
other. The front of the tank remained unscreened for
acclimation of the animals to feed under camera
lighting and while filming. Animals were fed daily
with a mix of live and freeze-dried Artemia sp.
through a clear vertically oriented PVC-tube (2.57 cm
diameter) that was positioned in the center of the
aquarium with its opening approximately 4 cm below
the water surface.
Experimental procedures
To vary the levels of intraspecific competition, three
microcosms with different numbers of conspecifics
were established. In the aquarium lacking competition
there was only one fish, low levels of competition
were represented by the focal fish plus two other
conspecifics, and high competition was represented
by the focal fish plus four other conspecifics.
Consequently, the most aggressive bluegill was
selected as the focal fish for the trials. The focal fish
was transferred to the filming tank alone or with other
fish, depending on the induced competition level. All
fish were housed individually in 40-liter aquaria
before being moved to the filming tank (40-liters,
51 cm L×31 cm H×26 cm D at 22°C), which was
screened on the sides and back such that the fish

Environ Biol Fish (2012) 93:13–21

could only see the fish which were present in the
filming tank. The fish were allowed to acclimate for
24 h after transfer and were not fed during this time,
after which they were filmed.
Using two High-Speed cameras, a Redlake Motionscope PCI 2000S and a Redlake Motionscope PCI 500
(Redlake MASD, Inc., San Diego, CA, USA), five preycapture events per treatment per focal fish were filmed at
250 fields per second to obtain a lateral and a dorsal
view of the prey-capture event. The dorsal image was
captured by one camera mounted vertically at 90° over
the water surface and directly over the feeding tube. The
second camera position in front of the aquarium
recorded a lateral view of the focal fish during prey
capture. The prey items, live Artemia sp. (average
0.5 cm length) were introduced one item at a time
through the clear PVC tube suspended in the middle of
the tank. Prey items were introduced approximately
5 min apart when the fish had moved away from the
feeding tube. Only prey capture events in which the
focal fish was lateral to the camera were used for
analysis. A maximum of ten Artemia sp. were fed to
the subject fish during any trial in order to eliminate
possible effects of satiation on the prey capture
kinematics (Sass and Motta 2002), although only the
first five successful prey capture events were used for
the analysis. Other fish present in the tank only
consumed two prey items throughout all the trials. As

five successful prey capture events were not always
obtained on 1 day, filming resumed after 24 h, during
which time the fish were not fed. After five successful
filming events, each focal fish was returned to its
individual holding tank alone. Each fish was only used
for one competition level treatment and was then
released or euthanized according to University protocol, except for the focal fish which experienced all
competition levels. Each focal animal was filmed five
times for three different competition treatments (no
competition, low competition and high competition).
This trial was repeated for a total of five focal fish
(n=5). The focal animals were identified from conspecifics by individual differences in their color
patterns and markings. Prey capture events in which
the mouth of the animal touched the feeding tube were
not considered successful prey capture events and were
not accounted for since this might have an effect on the
prey capture kinematics. Due to possible chemical cues
left by the fish while filming, the water was completely
changed after each filming session.

15

Data analysis
Feeding events were downloaded to a computer and
analyzed using MaxTRAQ Software version 1.87 (Innovision Systems, Inc., Columbiaville, Michigan, USA).
The following kinematic variables were analyzed from
the lateral sequences: peak gape of the mouth (Peak
Gape); time to open the mouth (TOpen); time to close the
mouth once reaching peak gape (TClose); and total time
of the gape cycle (TCycle). Peak Gape is defined as the

maximum distance between the two most anterior points
on the upper and lower jaw during the prey-capture
event. TOpen, as described by Sanford and Wainwright
(2002) eliminates the variability of early mouth opening
in bony fishes before prey-capture and is measured as
the time from 20% to 95% of peak gape. TClose is the
time from reaching Peak Gape to closing the mouth and
is measured from the field the mouth starts closing after
reaching Peak Gape to the field at which the mouth
reaches 20% of Peak Gape while closing. The 20% was
selected in order to be consistent with the TOpen
measurement and also to eliminate possible variation
in mouth closing. The gape cycle is measured as the
time from the field in which the mouth reaches 20% of
Peak Gape while opening to the field in which the
mouth reaches 20% of Peak Gape while closing. In
addition to the kinematic data the lateral filming
sequences were used to determine x and y coordinates
for the predator and the prey to determine the distance
moved by the predator and prey for each prey capture
event (Norton and Brainerd 1993). The distances the
predator and the prey (DPredator and DPrey) moved in the
time from reaching 20% of the peak gape while opening
the mouth until the prey disappeared in the mouth of the
predator were determined by tracking a spot on the
opercle of the fish and the head of the Artemia sp.
during the prey capture sequence. In addition, the
velocities of the predator and the prey (VPredator and
VPrey) were determined for the duration of the prey
capture event (TPrey), which is determined as the time

from when the mouth reaches 20% of the peak gape
while opening the mouth until the prey disappears in the
mouth of the predator. In addition, the running average
for the change in velocity of the predator (AInstantaneous)
was determined for each field of 10 sequential fields
before the prey entered the mouth of the predator and
used to determine if the predator maintained, increased
or decreased its velocity prior to prey capture for three
subjects under the different competition levels. An


16

increase in velocity between sequential fields therefore
indicates the fish is accelerating, whereas a decrease
indicates deceleration. In this manner the net acceleration or deceleration of the predator was calculated
across the 10 fields. The small sample size of subjects
occurred because this variable was determined post
hoc after the video sequences had been trimmed in
length.
To quantify the ram and suction components in the
prey capture events, the velocity and the distance
moved of the predator (VPredator and DPredator) was
used as an indicator for the ram component and the
velocity and the distance moved of the prey (VPrey
and DPrey) and the time to open the mouth (TOpen) as
an indicator for the suction component.
Statistical analysis
All variables obtained in this study were subjected to
a Two-Way Repeated Measures ANOVA using Sigmaplot Software version 11.0 (Systat Software, Inc.,

Chicago, Illinois, USA) to account for significant
differences (P<0.05) across treatments in a model
with repeated measurements for each focal animal.
The research was approved and followed the guidelines set forth by the University of South Florida,
Institutional Animal Care and Use Committee
(IACUC protocol #W3402).

Results
Behavior
The bold focal fish exhibited aggressive behavior
towards conspecifics once the feeding tube was
placed over the tank. During low and high competition scenarios, the focal animals constantly bit the
conspecifics and chased them away as they
approached the feeding tube. When the prey was
introduced into the filming tank, the focal animal
would rapidly swim towards the prey, capture it and
resume chasing away conspecifics which approached
the feeding tube.
Data analysis
Two-Way Repeated Measures ANOVA revealed that
increased intraspecific competition resulted in signif-

Environ Biol Fish (2012) 93:13–21

icant differences (P<0.05) in six out of nine variables
measured in the bold individuals (Table 1) in this
study. The field specific velocity (AInstantaneous) failed
normality even with transformation and underwent a
nonparametric Friedman’s Repeated Measures
ANOVA on Ranks. Time to open the mouth (TOpen)

decreased with increasing competition, when comparing no competition to low competition (P=0.011) and
no competition to high competition (P=0.003); Time
to close mouth (TClose) and the gape cycle (TCycle)
decreased as well when comparing no to high
competition (P=0.023; Fig. 1). Peak Gape showed
no significant difference with increasing competition.
The distance of the prey (DPrey; Fig. 2) decreased
with increasing intraspecific competition, being different when comparing no competition to low competition (P=0.040) and no competition to high competition
(P=0.003), whereas the distance of the predator
(DPredator; Fig. 3) showed no significant differences
across treatments. The velocity of the prey (VPrey;
Table 1) showed no significant differences with
increasing competition, however the velocity of the
predator (VPredator; Fig. 2) increased with increasing
intraspecific competition being different when comparing no competition to low competition (P=0.033) and
no competition to high competition (P=0.005). The
duration of the prey capture event (TPrey; Fig. 2)
decreased with increasing intraspecific competition,

Table 1 Average values for kinematic variables during prey
capture for five Lepomis macrochirus. Values are for five feeding
events each. Superscript letters denote significant differences
across treatments.*indicate variables with significant differences
(P<0.05), (ns) indicates no significant difference
Variable

Level of competition
No

Low

High

TOpen* (ms)

39A

27B

22B

TClose* (ms)

69

A

TCycle* (ms)

119A

76A,

0.6

0.7

0.3A

0.2B

DPredator

(ns)

(cm)

DPrey* (cm)
−1

VPredator* (cm s )

14.0

VPrey(ns) (cm s−1)
AInstantaneous* (cm s )
Peak Gape

(ns)

A

−10.4
41

(cm)

41

A

0.783

B

63B
0.1B

24.7
5.9
A

33B
0.7

B

6.4
−1

TPrey* (ms)

A, B

30.7B
3.9

A, B

+2.6

B

+7.2B

30

23B

0.907

0.897


Environ Biol Fish (2012) 93:13–21
0.050

A

Time (seconds)

0.040

0.030

0.020

0.010

0.000
NO

LOW

HIGH

Level of Competition
0.080

B

Time (seconds)

0.060

0.040

0.020

0.000
NO

LOW

HIGH

Level of Competition
0.140

C

0.120
0.100

Time (seconds)

Fig. 1 Average values
and ±1 SE for a) time to open
the mouth (TOpen), b) time to
close the mouth (TClose) and
c) the gape cycle (TCycle)
during prey capture for five
Lepomis macrochirus, at
three levels of competition.
The lines denote no
significant difference
between treatments

17

0.080
0.060
0.040
0.020
0.000
NO

LOW

Level of Competition

HIGH


18

Environ Biol Fish (2012) 93:13–21
0.30

35

A

B
30

Velocity (cm s )

0.20

25

-1

Distance (centimeters)

0.25

0.15

0.10

0.05

20
15
10
5

0.00

0
NO

LOW

HIGH

NO

Level of Competition

LOW

HIGH

Level of Competition

0.05

70

D

C

No Competition
Low Competition
High Competition

60
50

-1

Velocity (cm s )

Time (seconds)

0.04

0.03

0.02

40
30
20

0.01
10

0.00

0
NO

LOW

HIGH

-40

-30

Fig. 2 Average values and ±1 SE for a) the distance the prey
moved during prey capture (DPrey), b) the velocity of the
predator during prey capture (VPredator) and c) the duration of
the prey capture event (TPrey) for five Lepomis macrochirus. d)

-10

-0

Average velocity for ten fields prior to prey capture ±1 SE for
three Lepomis macrochirus. The lines in figures A, B, and C
denote no significant differences between treatments

0.70
No DPredator vs No DPrey

0.60

Distance Prey (DPrey) in cm

Fig. 3 The distances moved
by predator (DPredator) and
prey (DPrey) during prey
capture plotted against each
other at three levels of
competition for five
Lepomis macrochirus

-20

Time before Prey Capture (ms)

Level of Competition

Low DPredator vs Low DPrey
High DPredator vs High DPrey

0.50
0.40
0.30
0.20
0.10
0.00

0.00

0.20

0.40

0.60

0.80

1.00

Distance Predator (DPredator) in cm

1.20

1.40


Environ Biol Fish (2012) 93:13–21

being different when comparing no competition to low
competition (P=0.035) and no competition to high
competition (P=0.005). The average change in velocity
of the predator for ten fields prior to prey capture
(AInstantaneous; Fig. 2) increased (+7.2 cm s−1) significantly with increasing levels of competition, indicating
acceleration at high levels of competition, no significant change in velocity (+2.6 cm s−1) at low
competition and a negative change in velocity
(−10.4 cm s−1), at no competition indicating deceleration of the focal fish (P=0.028).

Discussion
This study, the first to investigate the effects of
intraspecific competition on the prey capture

kinematics in fish, demonstrates that bluegill
sunfish exhibit faster mouth opening and closing
times, shorter gape cycles and an increase in
predator approach velocity with increasing levels
of intraspecific competition. In contrast to previous studies, prey capture kinematics have been
shown to become slower (time to reach maximum
gape and lower jaw depression, time to close the
mouth) and last longer (duration of bite) at lower
water temperatures (Wintzer and Motta 2004;
Devries et al. 2006) and prey capture kinematics
are slower (lower jaw depression, max gape
distance, hyoid depression and recovery) with
increasing satiation (Sass and Motta 2002). However, this is the first study to reveal that intraspecific
competition for food modulates prey capture kinematics in fishes.
Competition in fishes has been widely studied,
including competition for food (Booth and Beretta
2004; Schleuter and Eckmann 2006; Ward et al.
2006), habitat (Almany 2004; Hasegawa and
Maekawa 2006; Kahl and Radke 2006) and reproduction (Taborsky 1998; Stoltz and Neff 2006; Plath
et al. 2008). Bluegill sunfish competing for the prey
item in this study exhibited two forms of food
competition: scramble and contest competition. In
scramble competition the focal fish reaches the prey
item before other fish, whereas in contest competition
the focal fish aggressively displaces its competitors
while pursuing the prey item (Ward et al. 2006).
Under both levels of competition the focal bluegill
sunfish reached the Artemia sp. prey first, and chased

19

away conspecifics which were approaching the
feeding tube.
During suction feeding the rapid expansion of the
buccal cavity generates a flow of water into the mouth
of the fish (Liem 1980; Norton and Brainerd 1993;
Carroll et al. 2004; Day et al. 2005) and faster mouth
opening times, as observed in this study (Fig. 1), can
be interpreted as an increase in buccal expansion rate
which leads to lower sub-ambient pressures within the
buccal cavity and higher flow speeds of the water in
front of the mouth (Sanford and Wainwright 2002),
therefore indicating an increase in inertial suction
force with increasing levels of competition. Fish may
perform compensatory suction to counter the bow
wave generated by the increased velocities of the
predator (Van Damme and Aerts 1997; Ferry-Graham
et al. 2003; Higham et al. 2005a), which could move
the prey away from the approaching predator. A
recent study on bluegill sunfish demonstrated the
formation of this bow wave when approaching prey
and how suction feeding reverses the flow and draws
the prey into the mouth (Holzman and Wainwright
2009). Therefore, more rapid mouth opening with
increased competition may be related to the increased
velocity of the predator and the need for greater
compensatory suction to counter the effects of a bow
wave generated by faster velocities during prey
capture. Faster mouth opening may also be due in
part to the higher predator approach velocity and the

force exerted on the opening mouth by the water.
The gape cycle was found to become shorter in
duration with increasing levels of intraspecific competition, which indicate faster prey capture events.
Therefore, the hypothesis that bluegill sunfish feed
faster at higher levels of competition compared to
lower levels of competition was confirmed.
Bluegill sunfish are characterized as ram and
suction feeders (Carroll et al. 2004; Day et al. 2005;
Higham et al. 2005b; Higham 2007) and utilized a
combination of ram and suction during prey capture
in this study. The bluegill sunfish exhibited higher
approach velocities during the prey capture event
(VPredator and AInstantaneous) with increasing levels of
intraspecific competition which are characteristic of
ram feeders and are usually utilized when capturing
elusive prey (Webb and Skadsen 1980; Norton 1991;
Porter and Motta 2000). The increased velocity is
indicative of an increase of the ram component during
prey capture. However, the apparent increase in


20

suction force with increasing competition is indicative
of an increase in the suction component during prey
capture. An increase in inertial suction force usually
manifests itself by drawing the prey towards the
mouth from a greater distance and at a higher velocity.
However, the distance the prey moved decreased
because the bluegill continued to accelerate as it

approached the prey to engulf it. The velocity of the
prey did not increase despite more rapid mouth
opening because the fish was perhaps employing
greater compensatory suction to overcome the bow
wave it was generating in front of the mouth.
Therefore it is concluded that both the ram and
suction components increased with increasing levels
of competition, however it was not possible to
confirm the second hypothesis that bluegill shift from
using primarily suction feeding to ram feeding with
increasing levels of competition.
Recent studies in fish behavior investigating the
bold-shy continuum have found that fish exhibiting
bold behavior are more willing to take risks (Wilson
et al. 1993; Webster et al. 2009). Individuals displaying higher risk behavior increased their reproductive
success as well as increasing predation risk which
could lead to early mortality whereas shy individuals
will exhibit behavior to avoid predation (Wilson et al.
1993; Webster et al. 2009). The focal bluegill sunfish
in this study were selected for bold behavior and it is
likely that the level of boldness could affect the prey
capture kinematics, since the latency to attack prey
has been shown to decrease in bold individuals
(Webster et al. 2009). This suggests that bold animals
may exhibit faster prey capture times compared to shy
animals.
In conclusion, this study demonstrated that prey
capture kinematics of bold bluegill sunfish are
affected by the presence of conspecifics while
competing for food. Increasing intraspecific competition resulted in faster mouth opening and

closing, shorter gape cycle time and increased
predator velocity during prey capture. However a
shift from suction feeding towards ram feeding with
increasing intraspecific competition was not confirmed in this study.
Acknowledgments The authors would like to thank the
Porter Family Foundation and the University of South Florida
Office of Undergraduate Research for funding this research as
well as Timothy Higham for offering comments on this

Environ Biol Fish (2012) 93:13–21
manuscript. We also would like to thank Ralph Turingan for
his help with the experimental setup, Richard Tankersley for his
help with the statistical analysis as well as Kyle Mara, Maria
Laura Habegger, Lisa Whitenack, Samantha Mulvany and
Tanya Brunner with their help throughout this study.

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Environ Biol Fish (2012) 93:23–30
DOI 10.1007/s10641-011-9886-z

Acoustic diversity in Lake Malawi’s rock-dwelling cichlids
Patrick D. Danley & Martin Husemann &
Justin Chetta

Received: 20 July 2010 / Accepted: 4 July 2011 / Published online: 17 August 2011
# Springer Science+Business Media B.V. 2011

Abstract The cichlids of Lake Malawi are one of the

world’s most species rich and phenotypically diverse
groups of extant vertebrates. The extraordinary
variability of this group’s color patterns, reproductive
behaviors, and trophic morphologies are well documented. More recently, an additional axis of phenotypic diversity has been identified. Lake Malawi
cichlids have been shown to use species-specific
acoustic communication in both aggressive and
reproductive encounters. However, documentation of
acoustic signals used by this group is limited to a
small number of taxa observed within the confines of
the laboratory. This study examines the acoustic
signals produced by six species spanning four genera
of rock-dwelling cichlids recorded in their natural
habitat, the shallow waters surrounding Thumbi West
Island, Lake Malawi. Four acoustic parameters were
quantified and compared between species: trill dura-

P. D. Danley (*) : M. Husemann
Department of Biology, Baylor University,
Waco, TX 76798, USA
e-mail:
J. Chetta
Medical Humanities Program, Baylor University,
Waco, TX 76798, USA
Present Address:
J. Chetta
Baylor College of Medicine,
Houston, TX 77030, USA

tion, number of pulses per trill, pulse duration, and
pulse period. Using these characteristics, sympatric

species within the genus Maylandia were easily
distinguished. Furthermore, a comparison of this data
to previously published acoustic data reveals possible
geographic dialects within species.
Keywords Mate choice . Sound production .
Cichlidae . Reproductive isolation . Speciation .
Metriaclima

Introduction
The cichlids of Lake Malawi have undergone one of
the most extensive and rapid radiations identified to
date. Since the formation of the lake basin 2 MYA,
well over 800 species of cichlid fish have diverged
from a single common ancestor. Most fish in this
system can be grouped into one of two major clades:
the rock-dwelling cichlids and the sand dwelling
cichlids (Albertson et al. 1999). These clades are
roughly equal in diversity and intense sexual selection
is believed to have played a significant role in
generating the extraordinary species richness in both
groups (Danley and Kocher 2001; Streelman and
Danley 2003). As a result, these fish have become a
model system for examining recent and rapid speciation events (Kocher 2004; Genner and Turner 2005).
Within the rock-dwelling cichlids, one of the most
likely and conspicuous targets of this intense selective


24

pressure is male nuptial color pattern. Male color

pattern is highly variable in Lake Malawi cichlids,
and, as a result, has been the focus of many
theoretical and empirical studies on the evolution
and diversification of species (van Oppen et al. 1998;
Carleton et al. 2006; Carleton 2009; Kidd et al. 2006).
However, additional cues such as olfaction and
acoustics have been suggested to play an important
role in mate choice (Robinson et al. 1998; Knight and
Turner 1999; Amorim et al. 2003; Amorim et al.
2004; Plenderleith et al. 2005; Cole and Stacey 2006;
Smith and van Staaden 2009). Furthermore, mate
choice experiments revealed that visual cues alone are
not sufficient to maintain species boundaries (Blais et
al. 2009). Hence, non-visual communication could be
of higher importance for the maintenance of species
boundaries within this system than currently thought.
Fishes can produce sounds in various ways.
Specialized skeletal muscles, filaments, pharyngeal
jaws and teeth (see Rice and Lobel 2002, 2004;
Amorim 2006 for review) can all be used to make
sounds. These sounds are then often amplified
through the use of the swimbladder as a resonance
body. Still, it is not exactly known how the majority
of cichlid fishes produce sounds. Ripley and Lobel
(2004) and Rice and Lobel (2004) suggested that the
pharyngeal jaw, its attached muscles and the swimbladder play an important role for sound production
in the Lake Malawi cichlid Tramitichromis intermedius. Lanzing (1974) proposed a similar mechanism
for the related species Oreochromis mossambicus.
Longrie et al. (2009) showed that O. niloticus
produces sound during a backward movement of the

pelvic and pectoral girdles and a forward movement
of the second pterygiophore of the anal fin. Still it is
not clear which sound production mechanisms apply
for the acoustic signalling in the rock-dwelling
cichlids of Lake Malawi.
Sounds produced by cichlids appear to act in a
variety of social interaction. Variations in acoustic
signals may be used for identification of conspecific
mates and the identification of male quality (Simões
et al. 2008a). Amorim et al. (2004), Longrie et al.
(2008) and Simões et al. (2008a) demonstrated that
cichlids produce sounds during antagonistic encounters and territorial defense as well in courtship.
Likewise, females produce sounds as warning or
aggressive signals towards each other (Simões et al.
2008a). Still, courtship appears to be the most

Environ Biol Fish (2012) 93:23–30

important situation in which acoustic signals are
emitted (Simões et al. 2008b). These observations
are consistent with the use of acoustic signals in a
wide variety of fish systems (see Lobel 1992, and
Amorim 2006 for reviews). They also illustrate the
potential for these signals to contribute to reproductive isolation.
Recently, interest in cichlid acoustic communication has increased and those few studies performed to
date have recorded sounds in captivity (but see Lobel
1998). These studies have shown that species can be
differentiated based on acoustic characteristics such as
trill duration, number of pulses per trill, pulse period,
pulse duration, and interpulse interval (Nelissen 1975,

1977, 1978; Lobel 1998, 2001; Amorim et al. 2004,
2008; Simões et al. 2006, 2008a). This study is the
first to directly examine the variation of acoustic traits
across several species of rock-dwelling cichlids in a
wild population. Here, we analyze four parameters of
acoustic signals produced by six closely related,
sympatric rock-dwelling cichlids of Lake Malawi.
We compare our data with previously published
studies on Lake Malawi cichlids, some of which
examined populations of the same species from
different locations.

Materials and methods
We examined male acoustic diversity of six species
spanning four genera of Lake Malawi cichlids:
Cynotilapia afra, Labeotropheus fuelleborni, Maylandia aurora, Maylandia callainos, Maylandia zebra,
and Petrotilapia nigra. (Debate has surrounded the
appropriate genus name for those species belonging to
what we refer to here as Maylandia. Other authors
may refer to this genus as either Pseudotropheus or
Metriaclima). All recordings were made in the
shallow water (<5 m) around Thumbi West Island,
Malawi (14° 01′27.58″ S 34°49′ 25.55″ E).
Males were observed for 20 min prior to recording
to identify breeding caves. Breeding caves were
identified through observing the focal male attempting to lead a receptive female to a specific area within
the rocky substrate. Previous studies have demonstrated that breeding caves are species-specific and
are occupied by a single territorial male (Hert 1989;
Danley 2001; Jordan et al. 2010). The hydrophone
was suspended in the center of male breeding caves

Environ Biol Fish (2012) 93:23–30

by wedging the hydrophone wire in the surrounding
rocks. Breeding caves were approximately 30 cm×
15 cm×25 cm [length × width × depth (Danley
2001)]. Given the placement of the hydrophone, we
assume that all the recorded acoustic data were
produced by the focal territorial male during courtship.
Visual data necessary to validate this assumption are not
available. All acoustic signals generated in this cave
were recorded for the subsequent 3.5 h.
Recordings were made using a HTI- 96 MIN
hydrophone (sensitivity: −163.9 dB 1v/uPA; frequency response: 2 Hz −30 kHz) and a Shure FP11
amplifier. Sounds were recorded using TDK IEC1
Type 1 cassette tapes with a Sony TCM-DV200DV.
Recordings were digitized using Audacity, converted
to ‘.wav’-format and input into RavenPro 1.3 software (Charif 2003). Only those trills with waveforms
distinct from background noise were analyzed. Oscillograms, spectrograms (frequency v. time), and power
spectra (frequency vs. power) were generated and
cross-referenced to measure the following four
parameters for all species: trill duration, pulse
duration, pulse period, and number of pulses per trill
(Amorim et al. 2004) (Fig. 1). Because the distance
between the hydrophone and the freely behaving focal
males were not controlled, center frequency (geometric mean between a lower and an upper frequency
threshold) and amplitude of the pulses were not
analyzed.
All statistical analyses were run using R 2.9.0 (The

R Foundation for Statistical Computing). All data

25

were log transformed prior to analysis. One-way
analysis of variance (ANOVA) was used to test for
significance in differences in each of the acoustic
components. Turkey’s HSD test was used for pair
wise comparisons.

Results
We were able to record sounds produced by one
focal male of each target species. Given the
placement of the hydrophone, it is assumed that
the recorded sounds were produced during courtship, however visual confirmation of this assumption is not available. The number of analyzable
trills recorded during the 3.5 h observation period
varied between species (Table 1): C. afra N=5, L.
fuelleborni N=4, M. aurora N=14, M. callainos N=
17, M. zebra N=12 and P. nigra N=6. Given the low
numbers of recorded trills of C. afra, L. fuelleborni
and P. nigra, data collected from these species are
presented but were not subjected to statistical
analysis.
Sounds produced by the Maylandia species
showed statistically significant differences in three
parameters: trill duration (Fig. 2a; F2,34 = 23.55, p<
0.0001), pulse duration (Fig. 2b, F2,37 = 100.16, p<
0.0001), and pulse period (Fig. 2c, F2, 39 = 92.76 p<
0.0001). Pulses per trill (Fig. 2d; F2, 40 = 2.83; p=
0.07) were not significantly different across the three

Maylandia species.

Fig. 1 Typical M. zebra trill; trill duration, pulse period, and pulse duration are indicated: a Oscillogram (amplitude in kU versus time
in seconds), b Spectrogram (frequency in kHz versus time in seconds), c Detail of a single pulse