natural food composition in the pond and digestive tract of striped catfish (pangasianodon hypophthalmus) during nursery stage

CAN THO UNIVERSITY
COLLEGE OF AQUACULTURE AND FISHERIES






NATURAL FOOD COMPOSITION IN THE POND
AND DIGESTIVE TRACT OF STRIPED CATFISH
(Pangasianodon hypophthalmus) DURING NURSERY
STAGE


By
NGUYEN LAM PHUONG NGOC


A thesis submitted in partial fulfillment of the requirements for
the degree of Bachelor of Aquaculture


Can Tho, December 2013


CAN THO UNIVERSITY
COLLEGE OF AQUACULTURE AND FISHERIES

NATURAL FOOD COMPOSITION IN THE POND
AND IN THE DIGESTIVE TRACT OF STRIPED
CATFISH (Pangasianodon hypophthalmus) DURING
NURSERY STAGE

By
NGUYEN LAM PHUONG NGOC

A thesis submitted in partial fulfillment of the requirements for
the degree of Bachelor of Aquaculture Science

Supervisor
Assoc. Prof. Dr. VU NGOC UT

Can Tho, December 2013


APPROVEMENT
The thesis “Natural food composition in the pond and digestive tract of
Striped Catfish (Pangasianodon hypophthalmus) during nursery stage”
defended by Nguyen Lam Phuong Ngoc, which was edited and passed by
committee on December 27 th, 2013.

Sign of Supervisor Sign of Student


Assoc. Prof. Dr Vu Ngoc Ut Nguyen Lam Phuong Ngoc

i

ACKNOWLEDGEMENT
First of all, I want to express my special thanks to my supervisor, Associate
Professor Dr. Vu Ngoc Ut for being invaluable guidance, advice, and
encouragement to my thesis completion.
Many thanks are also given to all other teachers of the College of Aquaculture
and Fisheries, and especially to those of the Department of Applied
Hydrobiology for providing me with great working and learning conditions.
I would love to express my sincere appreciation to miss Nguyen Hong Linh,
master student of Aquaculture Course 19 for her unconditionally kind help
throughout the experimental period.
Last but not least, I really want to thank my academic adviser, Dr. Duong
Thuy Yen, who was guiding and encouraging me over the last four years, and
my family, my friends in Advance Aquaculture Class Course 35 for their great
lifetime support which makes everything possible for me.

Nguyen Lam Phuong Ngoc

ii

ABSTRACT
Study on natural food composition in the pond and in the digestive tract
of Stripped Catfish (Pangasianodon hypophthalmus) during nursery stage
served as base for improving and enhancing survival rate of fry stage. The
study was carried out in Tien Thuy – Chau Thanh Hatchery of Ben Tre
Seafood Import – Export Joint Stock Company during 28 nursery days; fifteen
days collected sample in three nursery ponds. The samples were collected a
day before stocking fish, everyday in the first week and three day intervals.
The result obtained in nursery ponds showed that there were 140 species of
zooplankton including 36 species of Protozoa, 56 species of Rotifera, 17
species of Cladocera, 30 species of Copepoda and Nauplii. In the water supply
canal, 16 species of zooplankton were recorded includeding 5 species of
Protozoa, 6 species of Rotifera, 3 species of Cladocera, 2 species of Copepoda
and Nauplii. The density of zooplankton in the pond varied from 5,889 to
4,680,000 inds/m
3
and in the water supply canal varied from 2,778 to 250,000
inds/m
3
. In the digestive tract of the fry, 4 zooplankton groups were found.
Rotifera accounted for 5.16%, Protozoa 0.15%, Cladocera 68.29%, Copepoda
24.15% and Nauplii 0.83%. Result from natural food in the digestive tract

indicated that Cladocera was the most favorite food of Stripped Catfish in first
seven days after stocking and during nursery stage. These results showed the
abundant food selection of Stripped Catfish fry in nursery pond with many
different natural food compositions.
Keywords: Zooplankton, nursery stage, digestive tract.













iii

TABLE OF CONTENTS
ACKNOWLEDGEMENT i
ABSTRACT ii
TABLE OF CONTENTS iii
LIST OF FIGURES v
LIST OF TABLES vi
LIST OF ABBREVIATIONS vii
CHAPTER 1 INTRODUCTION 1
1.1 Background of study 1
1.2 Research objectives 2

1.3 Research contents 2
CHAPTER 2 LITERATURE REVIEW 3
2.1 Situation of Striped Catfish seed production in the Mekong delta 3
2.2 Biological characteristics of Striped Catfish 4
2.2.1 Classification 4
2.2.2 Distribution 4
2.2.3 Morphological characteristics 5
2.2.4 Nutritional characteristics 5
2.2.5 Growth characteristics 6
2.2.6 Reproductive characteristics 6
2.3 The role of natural food in aquaculture 7
2.3.1 Rotifer 8
2.3.2 Copepoda 10
2.3.3 Cladocera 12
CHAPTER 3 METHODOLOGY 14
3.1 Location 14
3.2 Time 14
3.3 Equipments 14
3.4 Sampling method 14
3.4.1 Fish specimens 14
3.4.2 Zooplankton sampling 14

iv

3.4.2.1 Qualitative analysis 15
3.4.2.2 Quantitative analysis 15
3.5 Sample analysing method 15
3.5.1 Zooplankton analysis 15
3.5.1.1 Qualitative analysis 15
3.5.1.2 Quantitative analysis 15

3.5.2 Fish sampling analysis 16
3.6 The method for data analysis 18
CHAPTER 4 RESULTS AND DISCUSSION 19
4.1 Zooplankton species composition 19
4.1.1 Zooplankton composition in nursery ponds 19
4.1.2 Zooplankton composition the water supply canal 19
4.2 The density of zooplankton composition 20
4.2.1 The density of zooplankton composition in nursery ponds 20
4.2.2 The density of zooplankton composition in the water supply
cannal 23
4.3 The zooplankton size in nursery pond 24
4.4 Mouth gap size of Striped Catfish in nursery stage 24
4.5 Natural food composition in the digestive tract in 28 nursery days 26
4.5.1 Frequency of food composition in digestive tract 26
4.5.2 Point counting of food composition in digestive tract 27
4.5.3 Combination point counting with frequency of food
composition in digestive tract 25
4.5.4 Coefficiency of food choice of Striped Catfish in 28 nursery
days 29
CHAPTER 5 CONCLUSIONS AND RECOMMENDATION 30
5.1 Conclusions 30
5.2 Recommendation 30
REFERENCES 31
APPENDICES 34


v

LIST OF FIGURES
Figure 2.1 The external image of Striped Catfish

Figure 2.2 Some species of rotifer
Figure 2.3 Some species of copepod
Figure 2.4 Some species of cladocera
Figure 4.1 The percentage of zooplankton species groups in nursery pond
Figure 4.2 The percentage of zooplankton species groups in the water
supply canal
Figure 4.3 The density of zooplankton (inds/m
3
) in nursery pond
Figure 4.4 The density of zooplankton (inds/m
3
) in the water supply canal
Figure 4.5 Mouth gap size of Stripped Catfish fry (µm) in 28 nursery days

v

LIST OF TABLES
Table 4.1 Mouth gap size of Striped Catfish in 3 nursery ponds
Table 4.2 Frequency (%) and the rate (%) of food composition in digestive
tract with age
Table 4.3 Analysing result of point counting of food composition in
digestive tract in 28 nursery stage
Table 4.4 Analysing result of food composition in digestive tract by
combination point counting with frequency
Table 4.5 Coefficiency of food choice of fry in 28 nursery days

v

LIST OF ABBREVIATIONS
µm Micrometer
Fig Figure
Inds Individuals
Kg Kilogram
Min Minimum
Max Maximum


1

CHAPTER 1
INTRODUCTION
1.1 Background of study
In recent years, aquaculture has been developed rapidly around the
world. Especially in Vietnam, the movement of culturing Striped Catfish has
developed exceeding planning production. Aquaculture provided 52% of
production and more than 60% value of exports in which Striped Catfish
reached high number of export turn over. Mekong Delta has the advantages
for culturing Striped Catfish. Can Tho, An Giang, Dong Thap provinces
provide large seed resources for aquaculture processing factory. In 2012, the

total production of Striped Catfish in the region reached nearly 4.6 billion
(increased nearly 2 times compared with 2011). According to Directorate of
Fisheries Statistics 2012, the region exported 53,000 tons of catfish, raised the
total amount of fish exported to 592,000 tons, valued at $1.6 billion.
Compared with 2011, the area of cultured pond increased 11.6% (5,300ha) but
the total value of exports fell by 2.2% due to Tra catfish price reduced from
0.2 to 0.4 USD / kg. Besides, catfish industry must be facing with difficulties
due to the shorten of materials. Commercial fish farming reach high efficiency
depends on many factors, the quality of fingerling is one of the decisive
factors.
Fingerlings are the important factor to help improve the quality as well
as production of Striped Catfish, at the same time; it increases profits and
minimizes risks for farmers. However, the quality of seed is decreasing
because famers have not cared about fingerling quality. In fingerling
production, food and feeding technique are very important in nursing fish.
Today, although there are many advanced techniques in the artificial food
production for larvae, but live food such as algae, rotifers, crustaceans, artemia
are still considered very important and have great potential in the seed
production. One of matters need special interest is shorten of natural food in
nursery stage. In fry stage, mouth size of larvae is small, the sensory organs as
eyes, touch, lateral line organs have not developed fully and the digestive
system is not complete; so limiting the selection and proper use of feed during
starting eating outside (Vu Ngoc Ut, 2012). In nursery stage, natural food
plays an important role in growth and survival rate. Natural food is the most
favorite food of fish in stage from fry to fingerling. Natural food compositions

2

affect to survival rate and fry quality in the pond. Especially, natural food
provides essential nutrient for larvae. Although there have been much

researches on the composition of fish food during nursery stage, they still are
not complete. This problem needs more investigable research in order to
ensure the survival and growth rate of fish. The experiments on “Natural food
composition in the pond and digestive tract of Striped Catfish
(Pangasianodon hypophthalmus) during nursery stage” will identify natural
food ingredients for nursery stage. Besides, it provides some information
about the efficiency of natural food in aquaculture.
1.2 Research objectives
To investigate the composition of natural food in the ponds and
digestive tract of striped catfish during the nursery stage to serve as base for
providing appropriate feeding regimes to improve survival rate of fish
fingerlings.
1.3 Research contents
- Investigation on natural food composition (zooplankton) in the pond
during the nursery period.
- Investigation of natural food composition in the digestive tract of fish
during the nursery period.

3

CHAPTER 2
LITERATURE REVIEW
2.1 Status of Striped Catfish seed production in the Mekong Delta
Mekong Delta is one of seven important economic regions of Vietnam.
Nature area is approximate 4 million hectare, about 12% total area of the
country (Directorate of Fisheries Statistics, 2009). From the first half of the
20th century, catfish farming in ponds began to practice in the Mekong River
Delta and had contributed to provisions for people. But in the dry season, the
amount of fish in the river was decreasing due to the fry river; fish was pulled
out of the sunken field so fish provided for market was scarce. Due to before
1970 fishery was restricted culturing techniques and fingerlings, most Striped
Catfish broodstock resources completely depended on nature. From the 1980s,
Mekong Delta had just begun to research and successed in Striped Catfish
artificial breeding after more than 30 years of natural breeding dependence.
However, until 1990s, farmers had just used widely fingerlings. Especially,
from 1999 to now, fingerlings supplied all Striped cultured sources with an
average output of 1.5 - 2 billion fish/ year. From only a few households until
now the whole area had 5,775 breeding households (Pham Van Khanh, 2006).
Thence, fry nursery industry began to develop and concentrated mainly in the
region as Tan Chau, Chau Doc, Hong Ngu, islands on Tien river as Long
Khanh, Phu Thuan. Early 1990s, fry yield catched anually reached only 150 –
200 million fries (Vuong Hoc Vinh, 1994). Nowaday, the demand of Tra
fingerling is about 1.8 to 2.4 billion fries every year. Mekong Delta has about
200 breeding hatcheries and 4000 households nursing fry on the density more
than 2,500 ha with total productivity is more than 2 billion fingerlings, fry
productivity in region meet livestock demand (Ministry of Agriculture and
Rural Development, 2012). In particular, provinces produce many Striped

Catfish fry are Dong Thap, Can Tho, and provinces have many nursing
hatcheries are Can Tho, An Giang, Dong Thap and Tien Giang. However, due
to the unstable fish material market that makes farmers feel less secure to
invest in production. Many households are not interested in seed quality,
production and business conditions do not also ensure regulations. Thereby it
causes loss in the rearing; the loss ratio exceeds 30% of the number of fish
stocked.


4

2.2 Biological characteristics of Striped Catfish (Pangasianodon
hypophthalmus)
2.2.1 Classification
Phylum Chordata
Subphylum Vertebrata
Class Actinopterygii
Order Siluriformes
Familia Pangasiidae
Genus Pangasianodon
Species Pangasianodon hypophthalmus


Figure 2.1 The external image of Striped Catfish
2.2.2 Distribution
Striped Catfish distribute in Mekong River Basin, present in all four
countries Vietnam, Laos, Cambodia and Thailand. In Vietnam, many years
ago, when there was no artificial broodstock, fry and fingerling, they were
usually captured on Hau and Tien River. Mature fish only found in the ponds,
rarely in the wild region of Vietnam, due to fish migrated up Mekong River to

live and find out where natural reproduction.





5

2.2.3 Morphological characteristics
Trương Thu Khoa and Tran Thi Thu Huong (1993) described Striped
Catfish as:
- Head large, flattened; mouth short, looked from the top to the tip the
mouthround.
- Terminal mouth, horizontal width, no stretch, arch shape and located on
the horizontal plane.
- Teeth small, smooth; palate teeth are divided into 4 small, slim patches
- Two barbels; extending maxillary barbel not beyond a vertical pectoral
fin margin; mandibular barbel shorter.
- Posterior naris closer anterior naris than eyes and in a straight line
drawn from the nose to the edge of the eye holes.
- Body elongate; lateral part flat; lateral line complete, branch, starting
from gill margin to the middle of caudal fin.
- The back of the spine of dorsal fin, pectoral fin serrate down the caudal
fin.
- Pelvic fin extending not touch posterior point of anal fin.
- In large fish, the back of body and head blue gray or brown black and
pale down abdomen, abdomen silver white.
- Pelvic fin and anal fin yellow.
2.2.4 Nutritional characteristics
After finishing the yolk sac, fry fish begin to use external food such as

rotifer, waterflea The common food of fingerling is not larger than the
diameter of the eyes, but for Striped Catfish, preys that they catch are much
larger than the diameter of their eyes (Pham Van Khanh, 2006). Artemia lavae
give high survival rate and best growth (Duong Thuy Yen, 2003).
Striped catfish is omnivorous but they have inclining to eat animals,
food from animals will help fish grow faster. In nature, fish eats organic
humus, aquatic roots, vegetable, shrimp, crab, insects, snail and fish. Fish in
culture pond can use different food as trash fish, pellets, bran, groat, spinach,
(Duong Nhut Long, 2004)


6

2.2.5 Growth characteristics
Striped catfish grows very fast, small fish grows length fast, fish
reaches 10 – 12 cm length, 14 – 15g weight in 2 months age. Fish grow
quickly from year 1 to year 3. After one year, the average weight is about
1kg/fish. After two year, fish reaches from 3 to 3.5kg/fish. Male fish grows
faster than female fish (Tran Van Vy, 2005). Fulton fat of fish increases
gradually with the weight and the fastest in the early years, males often has a
higher fat and they usually decrease as the breeding season. (Nguyen Chung,
2007).
2.2.6 Reproductive characteristics
In nature, reproductive season of Striped Catfish starts from May to
July yearly. Striped Catfish does not breed in culture pond. In Vietnam,
Striped Catfish does not breed ground in nature. Fish breed in Cambodia, fry
will be along the stream to Vietnam (Duong Nhut Long, 2004)
In artificial breeding, Striped Catfish can be raised early maturation and
spawned sooner than in wild, normally in March. Spawning in wild will not
get re-development state. But in artificial breeding condition, Striped Catfish

can be re-reproductive 1-2 times in year (Pham Van Khanh, 2006).











7

2.3 The roles of natural food in aquaculture
Natural foods are phytoplankton or zooplankton, benthic animals,
microorganisms, organic waste humus. Natural foods have many advantages
such as small size, suitable for larval mouth size, contain a large amount of
free amino acid, the peptic single circuit, unsaturated fatty acid polymer,
which contain natural enzyme system can resolve, which provide a full range
of nutrients especially for aquatic animals (Tran Thi Thanh Hien and Nguyen
Anh Tuan, 2009)
Fish is able to live and develop in the environment not meet the full
range of essential nutrients and especially small fish. In the larval stage, fish
use completely food from the outside; while the morphology can change a lot,
unstable, individual have to find food to survive when the body is too weak.
So food plays an important role in the existence and development (Pham Minh
Thanh and Nguyen Van Kiem, 2009).
Plankton is the natural food source of the larval stages of many
aquaculture species. The use of live feed in larval rearing therefore remains a

necessity in most aquatic organism hatcheries. In fact, most early stages of fish
larvae do not react to dry feeds and require live feeds that swim actively and
stimulate their omnivorous behaviour. In addition, larval fish usually do not
ingest or are not able to ingest formulated feeds (Guillaume Drillet, 2012).
In biology, zooplanktons are the second important link behind algae in
the natural chain, are direct or indirect food for shrimp and fish, especially in
larval stage. The development of zooplankton in basin affects to the
development of other species (Tran Suong Ngoc, 2009)








8

2.3.1 Rotifer
In classification system of Pechenik (2000), rotifer is determined as
Phylum: Rotifera
Class: Monogononta
Order: Ploima
Family: Brachionidae
Genus: Brachionus
Species: Brachionus angularis (Gosse, 1851)
Brachionus plicatilis (Muller)

Figure 2.2: Some species of rotifer
Rotifers are small, mostly freshwater animals, and are amongst the

smallest members of the Metazoa that group of multicellular animals which
includes humans, and whose bodies are organized into systems of organs.
Most of rotifers are about 0.5mm in length or less, and their bodies have a
total of around a thousand cells. This means that their organ systems are a
greatly simplified distillation of the organ systems found in the bodies of the
higher animals (Herbert Dartnall, 1978).
In culturing Dwarf Gourami larvae, the rotifers used as starter food
significantly improved the growth and survival of Dwarf Gourami larvae (Day
2 – 12). The use of rotifers would enable freshwater larviculture to improve
larval performance, increase yield, and facilitate breeding of new fish species
with small larvae (Lim L.C, Wong C.C, 1997).
After hatching 45 hours, Micronema bleeker start to nutrient outside.
Analysing of digestive organ of fish show that Copepoda larvae and rotifer are
the most abundant food in the digestive system of Micronema bleeke. It

9

suggests that fish begin eating zooplankton when they start eating outside
(Nguyen Van Trieu, et al., 2008).
Among the 13 species of Brachionus recorded during the present study,
B. angularis was the smallest in size. The smallest size and its shape may
enable them to be used as suitable live feed for the larvae having small mouth
opening, which in turn may lead to higher survival rate and enhanced fish
production (Molly Varghese, 2006).
In study about the potential competition and feeding impact of the
common rotifer species, Keratella cochlearis and K. quadrata, on the
abundant prostomatid ciliates, Urotricha furcata and Balanion planctonicum,
in laboratory batch culture experiments. All four species have similar feeding
preferences, co-occur in many freshwater environments, and are thus potential
competitors for the same algal food. Two small Cryptomonas species served

as food for the ciliates and the rotifers in the experiments. Growth rates of
each ciliate species were measured when they grew alone and when they were
paired with one of the rotifer species. Both rotifer species reduced the growth
rate of U. furcata, probably primarily by direct feeding on the ciliates. Growth
rate of B. planctonicum was unaffected by K. cochlearis, but was drastically
reduced by grazing and/or mechanical interference of K. quadrata. These
results suggest niche partitioning of the sympatric ciliates with respect to their
rotifer predators (Thomas Weisse, 2001).
In investigation about distribution of freshwater rotifer Brachionus
angularis in Hau river estuary and Can Tho-Hau Giang, in freshwater
ecosystem Brachionus angularis was discovered in flow-water ecosystem as
river or small irrigation canal from 433 to 1,111 ind/m
3
(around 5.2 to 17.7%
B. angularis/total of rotifers). In low pH water from 4 to 6; B. angularis
appeared in rice-field, ponds with density from 3700 to 31,050 inds/m3 and
2.9 to 6.6% B. angularis/total of rotifers. They were discovered in Hau river
estuary with low salinity (from 1 to 5‰) but no detection in tiger shrimp pond
in high salinity (fron 10 to 15‰) (Tran Suong Ngoc, 2009)




10

2.3.2 Copepoda

Figure 2.3 Some species of copepod
Copepods play major role in pond ecosystem, serving as food for small
fish, micropredators of fish and other organisms, fish parasite, intermediate

hosts of fish parasites and hosts and vectors of human disease. Plankton
animals, especially rotifers, cladocerans and copapods of the order Cyclopoida
are the most important food items in freshwater aquaculture and copepod
nauplii are especially valuable for feeding fry. Copapods used as natural food
are either cultured of collected from natural water bodies (Wojciech Piasecki,
2004).
Reports by Fryer (1957) indicate that Cyclops viridis is predatory;
among 51 guts examined he found approximately 22% with oligochaetes, 18%
with cyclopoid copepods, 16% with dipteran larvae, and 6% with cladocerans.
These figures suggest that the results obtained with Cyclops viridis and
Simocephalus vetulus may have been atypical since the copepods were forced
to exist on an unnatural diet. Another possibility is that not all of animals used
were Cyclops viridis since only a few were sent away for taxonomy
verification.
In some areas of Truong Sa Archipelago, study about natural food
sources serving aquaculture, zooplankton has variable species (81 species), in
which Copepoda has 41 species, accounting for 50.62% with average density
11,775 ind/m
3
. The density of zooplankton is high in some islands as Sinh
Ton, Thuyen Chai, Truong Sa. They are a good food source for shrimp and
fish (Nguyen Minh Nien, et al., 2012)
Through a study about assessing biodiversity and spatial of zooplankton
communities in the Cu Lao Dung mangrove ecosystem in Soc Trang province,
structure of species composition is different, in dry season and rainy season,
the density of Copepoda and nauplius larvae are dominant with the ratio 70 -

11

71%. Zooplankton composition in rainy season is higher than dry season.

Copepoda reaches the highest in dry season (13 species, 31%) because of a
different salinity between two seasons (Nguyen Thi Kim Lien, et al., 2013).
In a study of investigation suitable food for Copepoda (Microsetella
norvegica) culture Nguyen Thi Kim Lien, et al., (2006) found that mixture
algae consist of Isochrysis gallana, Chaetoceros calcitrans and Dunaliella
tertiolecta with 1:1:1 ratio is the best ration for the development of M.
Norvegica population on the single ration of each species.
In Tam Giang – Cau Hai brackish lagoon system, 43 species of
zooplanktons are identified, belonging to 24 genus, 18 families and 3 orders.
Among them, the Copepod is the most abundant with 37 species and occupies
86.04%. The second is the Cladocera with 5 species, accounting for 11.63%
and the last is the Rotatoria with 1 species, accounting for 2.33%. Families
have the most abundant are Acartidae (Copepoda) with 7 species, accounting
for 16.28%. The next is Pseudodiaptomidae (Copepoda) with 6 species,
accounting for 13.05%. Paracalanidae and Pontellidae (Copepoda) are 4
species, accounting for 9.30%. (Vo Van Phu and Hoang Dinh Trung, 2012)
In zooplankton composition in Phu Ninh Lake, Quang Nam Province,
Copepoda has the highest number with 15 species, accounting for 36.59%.
The next is Cladocera with 12 species, accounting for 29.27%, Rotatoria has 8
species, accounting for 19.51%, Ostracoda has 1 species, accounting for
2.43% and 5 nauplius, accounting for 12.2% (Vo Van Phu, et al., 2009).

12

2.3.3 Cladocera

Figure 2.4 some species of cladocera
Cladocera is a primarily freshwater monophyletic group, an important
component of the microcrustacean zooplankton. They inhabit most types of
continental fresh and saline water habitats, occuring more abundantly in both
temporary and permanent stagnant waters. Cladocera is an ancient group of
Palaeozoic origin. Cladocera have about 260 known species but the real
number of species is estimated higher 2 - 4 times (L.Forro, 2008).
Most cladocerans are filter feeders, straining water through the setae on
the endites of the limbs. Some species of the Sididae (e.g. Sida crystallina)
and Daphniidae (e.g. Simocephalus spp.) attach themselves to vegetation or
other substrates while they feed. Other cladocerans, such as Scapholeberis
spp., are associated with the water surface film, some swim among the
macrophytes or open water, such as Ceriodaphnia spp., and others, such as
Leydigia leydigi, are benthic. The Polyphemidae includes nine predacious
genera, such as Polyphemus pediculus, and have a reduced carapace which
frees the limbs to enable a grasping action (Hutchinson, 1967).
In brackish lakes in Eastern Spain, the microcrustacean community was
dominated by cladocerans at Poniente and Levante, by copepod at Reserva,
and by ostracods at Múrtulas. Numbers of cladocera recorded was much
higher at Levante and Poniente and extremely small at Múrtulas. Numbers of
cladocerans peaked in spring, from March to May, with a second peak in
September at Poniente. (Ann. Limnol, 2005)
Moina is antennae crustacean group (Cladocera) which is zooplankton
components primarily in freshwater aquaculture ponds. Moina is commonly
used in many different fish species rearing in the period from fry to fingerling
like Clariidae, snakehead, Tra catfish, anabas. Moina density in ponds is often

13

higher than the water body, especially in the previous fertilization pond (Vu
Ngoc Ut, 2012).
In Singapore, Moina micrura grown in ponds, fertilized with mostly
chicken manure or, less frequently, with pig manure, is used as the sole food
for fry of many ornamental tropical fish species, with a 95 - 99% survival rate
to ¾ inch (20 mm) in length quite common. Unfortunately, there is very little
information concerning practical mass culture methods of Moina, and the
available information is in mimeograph documents, foreign journals or other
scarce publications (R.W. Rottmann, 1992)
In L.Martin’s study, Moina Micrura can replace partially or completely
Artemia Nauplii during early postlaval culture of white shrimp Litopenaeus
schmitti. When applying Artemia and Moina in culturing postlarvae white
shrimp Litopenaeus schmitii, it was found that it does not affect survival,
growth rate, protease and α-amylase activities and resistance to osmotic stress.
The role of Moina becomes more important in freshwater fish larvae
nursery. In the stocking process, after moving water from 0.3 to 0.4m depth,
drop the eggs and eggs in order to ensure the amount of natural food for fish
fry immediately after release into the pond to limit the meat and each of them.
As a result of nursery Micronema bleeker, Nguyen Van Trieu (2008)
showed that after 30 nursery days, combining moina and rotifer raised survival
rate and growth ability.

14

CHAPTER 3
RESEARCH METHODOLOGY
3.1 Location
Sample collection was conducted in 3 nursery ponds at Ben Tre Import –
Export Joint Stock Company with sizes of:
+ Pond 1: 2,200 m
2

+ Pond 2: 2,300 m
2

+ Pond 3: 3,500 m
2

Sample analysis was conducted at College of Aquaculture and Fisheries,
Can Tho University.
3.2 Duration
The research was implemented from May to November, 2013.
3.3 Equipments
- Zooplankton net of 57µm mesh size, plastic bucket, plastic can, plastic

bottle, formol 40%,
- Recording book
3.4 Sampling methods
3.4.1 Fish specimens
- Fish fry were sampled for gut analysis with 30 specimens which were
randomly collected at each time.
- The fish were sampled before stocking, everyday in the first week and 3
days during the rest period.
- Fish specimens were then fixed with formalin (3-5%)
3.4.2 Zooplankton sampling
Zooplankton samples were also collected a day before stocking fish and
everyday in the first week and every 3 days during the rest period.




15

3.4.2.1 Qualitative sampling
- Samples were taken with zooplankton net which was dragged along the
edge of the pond with zigzag shape.
- The samples were stored in the 110ml bottle and fixed with 2-4%
formalin.
- Label with location, and time of sampling was sticked on the bottle.
3.4.2.2 Quantitative sampling
- Samples were collected at 5 points in the pond using a 20L bucket to
take water and filtered through the zooplankton net.
- The samples were then fixed with 3-5% formalin.
3.5 Sample analysing method
3.5.1 Zooplankton analysis

3.5.1.1 Qualitative analysis
The samples were observed under microscope and identified to species
based on available identification keys such as Shirota (1966), Round (1988).
3.5.1.2 Quantitative analysis
- The samples were counted under microscope with Sedgewick-Raffter cell
counter. Zooplanktons were counted in groups such as Protozoa, Rotifer,
Cladocera and Copepod.
- Every sample was counted 3 times with sub-samples. The density of
zooplankton was calculated by the following equations:
 
 
  
 
In which:
P: density (inds/m
3
)
T: total number of individuals counted.
A: area of counting square (mm
2
)
N: number of square counted
Vcđ: volume of sample period to counting (m
3
)
Vm: volume of water sample filtering through net (m
3
)