Study on species composition and some biological characteristics of eleotridae living in the bassac river

MINISTRY OF EDUCATION AND TRAINING
CANTHO UNIVERSITY

SUMMARY OF PhD THESIS
Major in Aquaculture
Identification code: 62620301

VO THANH TOAN

STUDY ON SPECIES COMPOSITION AND SOME
BIOLOGICAL CHARACTERISTICS OF ELEOTRIDAE
LIVING IN THE BASSAC RIVER

Can Tho, 2016
A


THIS STUDY HAS BEEN COMPLETED AT
CAN THO UNIVERSITY

Supervisors: Assoc. Dr. Tran Dac Dinh
Dr. Ha Phuoc Hung

The thesis was confirmed at the defence committee of Can Tho
University
Venue: ………………………………………………………………….
Time: ………………………………………………………………..….

Reviewer 1:
Reviewer 2:
Reviewer 3:

This thesis is available at:
Learning Resource Centre, Can Tho University.
Vietnam National Library.
B


CHAPTER 1: INTRODUCTION
1.1 General introduction
Goby has been the largest fish group with about 220 genera and 1,875
species belonging to five families (Eleotridae, Gobiidae, Periophthalmidae,
Apocrypteidae and Gobioididae) (Healey, 1971). Among them, Eleotridae
has comprised 31 genera and 178 species (Froese and Pauly, 2014). In the
Mekong river basin, there have been 34 genera and 101 species belonging
to five families (Rainboth, 1996). These five fish families are also found in
Vietnam, and Eleotridae consist of three genera and seven species (Mai
Dinh Yen, 1992; Nguyen Huu Phung, 1997; and Nguyen Nhat Thi, 2000).
Similarily, Tran Dac Dinh et al. (2013) showed that there were seven
species in Mekong Delta (MD) including: Eleotris melanosoma (Bleeker,
1853); Butis butis (Hamilton, 1822); Butis humeralis (Valenciennes, 1837);
Oxyeleotris marmorata (Bleeker, 1852); Oxyeleotris urophthalmus
(Bleeker, 1853); Bostrychus scalaris (Larson, 2008) and Butis
koilomatodon (Bleeker, 1849). Some species had economic values such as
O. marmorata, O. urophthalmus and E. melanosoma usually living in
inland areas and estuaries (Murdy, 1989), and in tropical and subtropical
areas (Chotkowski et al., 1999). Many spcecies came there for spawning
and completing lifecycle (Blaber et al., 2000). Species of O. marmorata
was raised and catched at fishing areas along in Bassac river, in which
species of O. urophthalmus and E. melanosoma had economic values
because of meat delicious and highly productive (MOFI, 1996). However,

they were not been much studying and only some studies were done on
species of diversity and their biological characteristics. Presently,
knowledge of those species, the abundance of species of Eleotridae living in
Mekong river basin, as well as nutritional characteristics and reproductive
biology of O. urophthalmus and E. melanosoma were not much announced
although they were among of the groups with high economic values in the
MD. So, study on species composition of Eleotridae and biological
characteristics of gobies were very essential.
1.2 General objective of study
The overal objective aims to determine of species, abundance of Eleotridae
and biological characteristics of gobies living in Bassac river in the
contribution to the protection of aquatic resources products and providing
the basis for researching on artificial breeding of some gobies having
economic value in the future.

1


1.3 The significance of the thesis
The results of this thesis to supplement scientific data about the species of
Eleotridae and biological characteristics of gobies living in Bassac river.
These results were used as resources for teaching and scientific researching
in order to manage, restore and regenerate fisheries resources in general and
particular groups of goby.
1.4 The significant results
i) Survey resulted some ecological parameters showed that the salinity was
related to the living in gobies of Eleotridae, especially species of E.
melanosoma and B. butis. Catch per unit effort (CPUE) of these species
had seasonal fluctuations and depended on the diversity of aquatic
species, flow speed and water depth.

ii) There were five species of Eleotridae living in Bassac river, in which
species of E. melanosoma, O. urophthalmus and O. marmorata appeared
more in upstream and middle while B. Butis appeared in the middle and
downstream, especially species of Butis humeralis appeared only in the
downstream. However, catched by trawl net showed that species of E.
melanosoma appeared in the upstream and middle, while B. butis just
appeared in the downstream. CPUE of E. melanosoma was more B.
Butis. The abundance in rainy season was more in dry season.
iii) Species of E. melanosoma and O. urophthalmus had morphological
gastrointestinal tract matching animal feeding. Although there were four
groups of food appeared in nutritional spectrum, but only three groups
were considered as the favorite food for these species (crustaceans,
molluscs and fingerling). The ratio of kinds of food also changed with
increasing the total length and width of their mouth.
iv) The value of gonadosomatic index (GSI) of E. melanosoma and O.
urophthalmus was high from May to October, while the hepatosomatic
index (HSI) was low in July; conditional factor (CF) was highest in
April and November showing that reproductive seasonality of this two
species was along from May to October and concentrated from May to
July. The results also showed that the fecundity species of E.
melanosoma ranged from 49 to 930 eggs/g of female and higher than O.
urophthalmus (from 44 to 477 eggs/g of female). Absolute fecundity of
E. melanosoma from 2,981-19,520 eggs/ female and O. urophthalmus
from 1,290-9,999 eggs/female. Length of maturity (Lm) of E.
melanosoma was 8.62 cm (in male) and 7.79 cm (in female); while Lm of
O. urophthalmus was 11.36 cm (in male) and 7.96 cm (in female).
2


CHAPTER 3: MATERIALS AND METHODS

3.1 Time and site study
This study was carried out from August 2012 to December 2014. The study
sites were in the upstream (An Giang province), middle (Can Tho city) and
downstream (Soc Trang province) in Bassac river (Figure 2.1).

Figure 2.1: Diagram sampling areas in Bassac river
(www.maps.google.com, accessed on 05/06/2012)
3.2 Materials and methods of study
3.2.1 Study 1: Identify some ecological parameters (temperature, pH,
salinity, water flow, water depth, phytoplankton, zooplankton and
zoobenthos) in Bassac river
Identifying some ecological parameters in the target areas was performed
from August 2012 to June 2013 at the same time and place of gobies that
collected by trawl net in the upstream, middle and downstream in Bassac
river. Each area collected five points, sampling cycle two months, in which:
a) Value of pH, temperature and salinity of the water were determined by
the used of specialized equipment: pH meter, thermometer,
refractometers at the field (Figure 2.2).
b) Water flow was determined by the flowmeter (23090; Paul and Sally,
1977): Water flow (km/h)=distance measurement (km)/measurement
time (hours); in which: (i) distance measurement=(number of rotor ring
turned rotor x coefficient)/999999; and (ii) coefficient for flowmeter
rotor (23090)=26,873 (Paul and Sally, 1977).
c) The depth of water in the survey was measured in the field with a water
depth measurement device (model PS-7FL Hondex) (Figure 2.2).
3


Device of water depth measurement

Device of refractometers

Thermometer and GPS
pH meter
Figure 2.2: Some of devices used to collection of ecological parameters

d) Species composition of phytoplankton, zooplankton and zoobenthos by
phytoplankton net (mesh size of 30 micrometers), zooplankton net
(mesh size 60 micrometers) and bottom Petersen (0.028 m2) combined
with grating (500 micrometers), was collected at 15 points in three
areas on Bassac river. After collecting the sample in 110 ml plastic
bottle with formaline fixed concentration of 2-8% (Petersen, 1990),
phytoplankton samples were formaline fixed within 2%, zooplankton
4% and zoobenthos 8%. Then they were analyzed by microscope
objective lens in observing E10 at laboratories, Colledge of aquaculture
and fisheries, Can Tho university.
+ Determining the species composition of phytoplankton, zooplankton
and zoobenthos was based on Shirota (1966), Duong Duc Tien and Vo
Hanh (1997), and Carmelo et al. (1996).
+ Determining the density of phytoplanktons, zooplanktons and
zoobenthos was based on Boyd and Tucker (1992).
 Density of phytoplanktons:
X (ind./L) = (T*1.000*Vcondensed *103)/(A*N*Vsample)
In which:
T: Count the number of phytoplankton in each sector
Vcondensed: Volume of condensed sample
A: Area of one cell of sedgewick rafter cell S50
N: Number of cell of sedgewick rafter cell S50
Vsample: Volume of sample collection by phytoplankton net

4


 Density of zooplankton:
X (ind./m3) = (T*1.000*Vcondensed*106)/(A*N*Vsample)
In which:
T: Count the number of phytoplankton in each sector
Vcondensed: Volume of condensed sample
A: Area of one cell of sedgewick rafter cell S50
N: Number of cell of sedgewick rafter cell S50
Vsample: Volume of sample collection by phytoplankton net

 Density of zoobenthos:
D (ind./m2) = X/(N*d)
In which:
X: Count the number of zoobenthos in each sector

N: Number of collection by zoobenthos Petersen
D: Area of mouth zoobenthos Petersen (d=0.028 m2)

3.2.2 Study 2: Determine species of Eleotridae and abundance (CPUE)
of gobies living in Bassac river
Samples were collected by fishing, gillnet, trawl and directed collection of
fishermen from fishing activities in study sites include the type of fishing
such as bottom nets, fishing, put swamps nets, rubs and trawl. Fish samples
kept with ice and analyzed at the laboratory of fisheries resources, Can Tho
university. These indicators of morphological analyzed consists of:
+ Rate of standard length (cm) / head length (cm)
+ Rate of standard length (cm) / body height (cm);
+ Rate of head length (cm) / distance of between eyes(cm);

+ Rate of head length (cm) / snout length (cm);
+ Rate of edges length (cm) / height edges (cm);
+ Rate of body height (cm) / height edges (cm).
Table 2.1: Number of sample to determine of morphological criteria of Eleotridae
Unit: individual/species
Eleotris
Oxyeleotris
Oxyeleotris
Species
Butis butis
Butis humeralis
melanosoma
urophthalmus
marmorata
Number
45
50
36
41
54

The classification system in this study weas identified from level of family
(Eleotridae) according to Lindberg (1971) (cited by Kanayama, 1991), the
species level was mainly based on Smith (1991). Also, refer to the
documents classified by the authors as: Cuvier and Valenciennes (18281848), Cantor (1848) (cited by Manilo and Bogorodsky, 2003), Taki
(1974), Vuong Di Khang (1962). Three genus of Eleotridae were
determined according to the following classification keys:
1.a- Skeletal gill covers front edge after one spiky toward to front ….... Eleotris
2.a- Thin scalp, the forehead between the eyes, skull clearly emerged. It was
covered by scales comb. The lateral line along was 26-30 ......................... Butis

2.b- Thick scalp, skull covered. Head and body covered the front of circular
scales, flakes coated part after brush. The lateral line along was 60-90
……………………………………………………......…..………… Oxyeleotris
5


In this study, refer to the documentation of Mai Dinh Yen (1992), Truong Thu
Khoa and Tran Thi Thu Huong (1993), Nguyen Nhat Thi (2000), Tran Dac
Dinh et al. (2013), Froese and Pauly (2014) to identify of gobies.
Determining the extent of relative abundance (CPUE) of Eleotridae was
collected by trawl net with technical parameters: width at 4.5 m, height at
0.5 m, mesh size in the mouth and body at 25 mm, in refuge at15 mm, with
cycle sampling in two months. Location of sampling points in Bassac river
on tributaries river (from the main river enters 1 km, was located along the
main river) started from upstream and downstream in the area of An Giang,
Can Tho and Soc Trang; each area collected five points, three points earned
in main river and tributaries at two collection points, location of points
earned was determined by GPS (Global Positional System).

A) Pelvic fins separately
B) No lateral
C) Two separate dorsal fins, include hard
rays and soft rays
D) Films bring discontinuous
Figure 2.3: Some of major morphological characteristics of goby (Tran Dac Dinh at al., 2013)

3.2.3 Study 3: Study on nutritional characteristic of Eleotris
melanosoma and Oxyeleotris urophthalmus
Gobies samples were collected from June 2013 to May 2014, sampling
cycle was once for two months at different size groups. Each group

collected at least 30 individuals per species (Table 3.2).
Table 3.2: Number of samples analyzed nutritional spectrum of E. melanosoma and O. urophthalmus
Unit: individual/species/month
Rainy season (2013)
Dry season (2014)
Species
Total
June August
October
January
March May
E. melanosoma
53
56
61
45
49
38
302
O. urophthalmus
59
40
42
42
36
34
253

Gobies samples were fixed in formaline fluid with concentrations of 10%,
then brought to the laboratory of aquatic resources fisheries, Can Tho

University to analyze. Method of determining feeding habits of goby based
on morphological and structure of the digestive organs (shaped teeth,
mouth, combs bearing, intestine length and types of food in the digestive
tract). Food was removed from the gastrointestinal tract to 1 liter of distilled
water, shake well and take 100 ml continuing shake, then take 1 ml for
counting chamber (sedgewick rafter cell S50) and put on the microscope
observation, analyzed by the method of frequency of occurrence (Hynes,
1950) and methods of weigth (Pillary, 1952).
6


2.2.3.1 Method of determined the morphological and structure of digestive
organs
Samples of E. melanosoma and O. urophthalmus obtained from Table 3.2
were analyzed identifying indicators: the width of mouth, length and body
length of their intestine (Pravdin, 1973). To determine their feeding habits
based on the correlation between the length of intestines and body length of
gobies (relative length of the gut-RLG). RLG was calculated according to
Al-Hussaini (1949): RLG=length intestine (cm)/ body length (cm) (RLG<1:
feeding animals; RLG=1: omnivorous; RLG>1: herbivorous).
2.2.3.2 Method of determining the nutritional spectrum
+ Methods of frequency of occurrence: The number of goby stomach
presence of every type of food was calculated. The percentage (%) of total
number in stomach was observed, according to classified documents about
the animal and aquatic plants of Shirota (1966), Duong Tien Duc and Vo
Hanh (1997) and Carmelo et al. (1996).
+ Method of weight: Most species of Eleotridae food ingredients of animal
origin with a large weigth, so this study method was used in conjunction
with the weigth and frequency of occurrence method to determine the food
spectrum of E. melanosoma and O. urophthalmus in two steps: (i) use of

electronic scales (3 decimal places) of the total mass balance of each type of
food in the stomach of fish; and (ii) the weigth of each type of food to be
converted into a percentage (%) of the total weigth of each food in stomach.
3.2.4 Study 4: Study on reproductive biology characteristic of Eleotris
melanosoma and Oxyeleotris urophthalmus
Samples were collected from August 2012 to July 2013 and sampling cycle
was once a month. The analysis criteria includes:
(i) Stages of sexual maturity: based on six steps sexual maturity
recommended by Nikolsky (1963) and combined with histological
methods of Drury & Wallington (1980) and Kiernan (1990).
(ii) Rate of male and female: observed morphological characteristics and of
gobies gonads to determine gender.
(iii) Gonadosomatic index (GSI): defined for each month, GSI
(%)=(GW/BW)*100 (GW: weigth of fish gonad; BW: body weight).
(iv) Hepatosomatic index (HSI) was also determined for each month.
HSI(%)=(LW/(BW)*100 (LW: liver weigth; BW: body weight of fish).
(v) Correlation of length-weight, condition factor (CF): determining to the
correlation between the length-weight based on Huxley (1924):
W=a*Lb (W: total weight; L: total length; a and b: coefficients).
Condition coefficient (CF) was determined: CF=W/Lb (W: body
7


weight; L: total length; b: coefficient was determined based on the
equation: W=a*Lb).
(vi) Breeding season of them was determined basing on the result of
determining stage of sexual maturity, GSI, HSI and CF.
(vii) Fecundity: determined basing on weigth of ovary, and representative
sample of eggs was taken at three positions (beginning, middle and end
of ovary). Absolute fecundity identified: PF=(n*G)/G (G: weigth of

ovary (g); g: total body weight (g); n: number of representative samples
of eggs (egg). Relative fecundity identified: RF=PF/BW (PF: absolute
fecundity; BW: body weight) (Banegal, 1967).
(viii) Mature length (Lm): the maturity length at which 50% of the total
number of individuals in populations grow to maturity stage (stage III)
(King, 1995). Curvature of P is expressed through the equation: ln [(1P)/P] = r*r*Lm-L, curve of this equation with linear (y=ax+b), original
coefficient a=-r and launched the original b=r*Lm, using regression
methods will determine Lm= -b/a and in this study was determined by
software Stat 8.0.
CHAPTER 4: RESULTS AND DISCUSSION
4.1 Identify ecological parameters (temperature, pH, salinity, water
flow, depth, phytoplankton, zooplankton, zoobenthos) in Bassac river
4.1.1 Physical indicators (pH, temperature, salinity)
Results showed that the pH value was little changed through six times
survey (7.6-8.1), temperature from 29.1-30.9oC, salinity in the downstream
appeared only in February, June and December, salinity in rainy season
from 0 to 7.6 ‰ and fluctuate less than the dry season (2-10.8‰). Results
also showed that pH and temperature fluctuates seasonally (Figure 4.1).
According to Cees et al. (1995), some gobies living in salinity up to 25‰,
but they lived in various types of water basins with different salinity, and
they lived in an environment with temperature fluctuating large (28.731.9oC) even to 36.8oC.
8.5

32

Rainy season

Dry season

Temperature (oC)

Value of pH

31
8.0

7.5

30

Upstream

Middle
Surveyed areas

Downstream

8

Rainy season

Dry season

7
6
5

4

29

3

28

2
1

27

7.0

9

Dry season
Salinity (%o)

Rainy season

Upstream

Middle
Surveyed areas

Downstream

0

Upstream

Middle

Downstream

Surveyed areas

Figure 4.1: Fluctuations of pH, temperature and salinity in three areas surveyed

4.1.2 Water flow and water depth
Water flow had many variations (0.1-1.3 km/hour); the locations of water
8


flow in the middle and downstream was lowest (0.1 km/hour) and highest in
the upstream (1.3 km/h) (Figure 4.2).
The water depth at the three regionals fluctuated (4.3-14.4 m), in which the
water depth in the middle was highest (8.7±2.7 m) and lowest in the
upstream (6.8±3.0 m) (Figure 4.2). According to Dang Ngoc Thanh et al.
(2002), distribution of benthos organisms depended on the water depth,
vertical hydro static water bodies in coastal areas with sediments, molluscs
and shellfish groups developed more depths.
18
Rainy season

Dry season

Dry season

16

1.4

Water depth (m)

Water flow (km/hour)

1.6

1.2
1.0
0.8

0.6

Rainy season

14
12
10
8
6
4

0.4

2

0.2

0

0.0
Upstream

Middle

Upstream

Downstream

Middle

Downstream

Surveyed areas

Surveyed areas

Figure 4.2: The water flow and water depth in the three areas surveyed

4.1.3 Species of aquatic
4.1.3.1 Phytoplankton: There were 31 species of phytoplankton appeared at
upstream, 22 species appeared at middle and 15 species appeared at
downstream; in which cyanophyta, bacillariophyta and chlorophyta
dominated (18-41%), while euglenophyta, dinophyta and chrysophyta less
(1- 9%) (Figure 4.3).
Chrysophyta
(9%)

Euglenophyta

(1%)

Dinophyta
(1%)
Bacillariophyta
(29%)

Cyanophyta
(18%)

Chlorophyta
(41%)

Figure 4.3: Structure of phytoplanktons in the three areas surveyed

Frequency of occurrence species of phytoplanktons in rainy season higher
in dry season. In which, cyanophyta, bacillariophyta and chlorophyta more
and concentrated in the upstream and middle (Figure 4.4).
11

11

8
7
6
5
4
3

2

11
10

10

Rainy season

Dry season

9

8
7
6

5
4
3

2

Bacillariophyta

Chlorophyta

Cyanophyta

Chrysophyta

Euglenophyta

Dinophyta

8
7
6
5

4
3
2

0

0

0

Rainy season

9

1

1

1

Dry season

Rainy season
frequency of occurrence (ind.season)

Dry season

9

Frequency of occurrence (ind.season)

Frequency of occurrence (ind./season)

10

Bacillariophyta

Chlorophyta

Cyanophyta

Chrysophyta

Euglenophyta

Dinophyta

Bacillariophyta

Chlorophyta

Cyanophyta

Chrysophyta

Upstream
Middle
Downstream
Figure 4.4: Frequency of occurrence of phytoplanktons in three areas surveyed

9

Euglenophyta

Dinophyta


Density of phytoplanktons in the upstream and downstream higher middle
(Table 4.1). In the upstream highest in dry season (28,545±20,190 ind./L),
euglenophyta was lowest (1,646±720 ind./L), highest in the middle of
chlorophyta (5,333±3,479 ind./L) and lowest of euglenophyta (1,633±809
ind./L), highest in downstream (25, 59±28,583 ind./L) and lowest was
cyanophyta (86±33 ind./L) and density of bacillariophyta highest in the
upstream and downstream, lowest in the middle.
Table 4.1: The average density of phytoplanktons in three areas in Bassac river
Area
Upstream
Middle
Downstream

Season

Dry season
Rainy season
Dry season
Rainy season
Dry season
Rainy season

Bacillariophyta
28,545±20,190
10,294±2,186
4,586±1,017
6,986±3,060
25,759±28,583
2,239±862

Unit: individual/Liter
Cyanophyta
Chlorophyta
9,321±5,581 4,471±2,260
20,761±16,484 7,026±9,685
2,036±680 5,333±3,479
4,921±2,772 5,324±3,452
2,730±3,030
0
86±33
0

Euglenophyta
1,646±720
2,894±1,971

1,633±809
3,703±2,067
0
0

4.1.3.2 Zooplankton: Structure of zooplankton species occured in three
areas, rotifera appeared total 111 species and 53 genus; in which protozoa
has 51.4%, rotifer has 25.2%, copepoda has 18.9 and cladocera has 3.6%.
However, veliger (class of bivalvia larvae) appeared very few (0.9%) in the
upstream and middle (Figure 4.5). This results was similar to Duong Tri
Dung and Nguyen Hoang Oanh (2011), zooplankton species in the middle
(canal Cai Khe) has 79 species and 54 species, in which rotifer was highest;
however, this results higher of Ngo Duc Chan (2010) in the downstream has
48 species.
Veliger
(0,9%)

Copepoda
(18,9%)
Cladocera
(3,6%)

Rotifera
(25,2%)

Protozoa
(51,4%)

Figure 4.5: Structure of zooplanktons in the three areas surveyed
40

40

Dry season

25
20
15

10
5

35

Rainy season

Dry season

30
25
20
15
10
5

0

Rainy season

35

Dry season

30

25
20
15
10
5

0

Protozoa Rotifera Cladocera Copepoda Veliger

Frequency of occurrence
(ind./season)

40

Rainy season

30

Frequency of occuurence
(idn./season)

Frequency of occurrence
(ind./season)

35

0

Protozoa Rotifera Cladocera Copepoda Veliger

Protozoa

Rotifera Cladocera Copepoda Veliger

Upstream

Middle
Downstream
Figure 4.6: Frequency of occurrence of zooplanktons in three areas surveyed

Density of zooplanktons in rainy season was higher in dry season, the
10


lowest in the middle and highest in downstream (Table 4.2). In which,
density of Cladocera in the upstream highest (3,793±3,760 individuals/m3),
Copepods in upstream lowest (1,037±361 individual/m3), density larval of
Nauplius highest in the middle (2,741±1,935 individual/m3), while density
of Protozoa was lowest in the middle (696±630 individual/m3), and density
of Protozoa highest in downstream (35,408±38,256 individual/m3).
Table 4.2: The average density of zooplanktons in three areas in Bassac river
Unit: individual/m3
Area
Upstream

Middle
Downstream

Season
Dry season
Rainy season
Dry season
Rainy season
Dry season
Rainy season

Protozoa
1,334±1,218
696±630
493±237
956±656
13,935±14,391
35,408±38,256

Rotifera
1,111±868
2,822±2,437
492±240
2,185±1,022
2,796±1,881
7,058±6,204

Cladocera
3,259±3,532
3,793±3,760

1,137±376
637±342
178±308
894±1,344

Copepoda
1,037±361
3,437±3,879
696±333
815±334
537±465
3,081±2,543

Nauplius
1,518±525
2,741±1,935
1,222±446
2,274±1,344
4,702±3,500
9,584±10,147

3.1.3.3 Zoobenthos: There were 73 species (upstream: 17 species, middle:
23 species, downstream: 33 species) with 6 classes: Gastropoda, Bivalvia,
Crustacea, Insecta, oligochaeta and Polychaeta. In which, there were 12
species of Gastropoda highest (36%), Bivalvia 8 species (24%),
Oligochaeta 4 species (12%), Crustacea 4 species (12%), Polychaeta 3
species (9%), Insecta 2 species (6 ,%). This result was higher than the
downstream (16 species) (Vu Ngoc Ut and Duong Thi Hoang Oanh, 2013).
Crustacea
(12%)

Insecta (6%)

Oligochaeta
(12%)

Bivalvia
(24%)

Polychaeta
(9%)

Gastropoda
(36%)

8

Rainy season

7

Dry season

6
5
4

3
2

Frequency of occurrence
(ind.season)

Frequency of occurrence
(ind.season)

8

Rainy season
Dry season

7
6
5

4
3
2

1

1
Oligochaeta Polychaeta Gastropoda

Bivalvia

Crustacea

Insecta

8

Rainy season

7

Dry season

6
5
4
3
2
1

0

0

Frequency of occurrence
(ind.season)

Figure 4.7: Structure of zoobenthos in the three areas surveyed

Oligochaeta Polychaeta Gastropoda

Bivalvia

Crustacea

Insecta

0
Oligochaeta Polychaeta Gastropoda

Bivalvia

Crustacea

Insecta

Upstream

Middle
Downstream
Figure 4.8: Frequency of occurrence of zoobenthos in three areas surveyed

Density of zoobenthos in rainy season was higher compared to dry season.
In which, in the upstream and middle higher downstream (Table 4.3). In the
upstream Oligochaeta has the highest density (82±57 ind./m2) and lowest
was Gastropoda (7±1 ind./m2); in the middle density of Bivalvia highest
(58±17 ind./m2) and lowest was Insecta (1±1 ind./m2), while downstream
11


density of Bivalvia has the highest (60±85 ind./m2) and lowest has
Crustacea (8±6 ind./m2), Insecta and Oligochaeta does not appear.
Table 4.3: The average density of zoobenthos in three areas in Bassac river
Unir: individual/m2
Area

Upstream
Middle
Downstream

Season
Dry season
Rainy season
Dry season
Rainy season
Dry season
Rainy season

Oligochaeta

Polychaeta

Gastropoda

Bivalvia

Crustacea

Insecta

25±7
82±57
16±11
38±4
0
0

15±14
23±4
18±14
55±3
30±22
12±14

63±43
7±1
28±17
24±6
12±15
21±30

83±19
11±10
55±41
58±17
60±85
53±34

50±30
16±20
15±15
50±39
8±6
17±26

55±17

8±5
9±9
1±1
0
6±13

4.2 Study on species of Eleotridae and abundance (CPUE) some of
gobies in Bassac river
4.2.1 List of species (Eleotridae)
There were five species appeared included: Eleotris melanosoma,
Oxyeleotris urophthalmus, Oxyeleotris marmorata, Butis humeralis and
Butis butis. In which, species of B. humeralis appeared only in areas
downstream and species of B. Butis appeared in the upstream and
downstream; however E. melanosoma, O. urophthalmus and O. marmorata
occured in the upstream, middle and downstream in Bassac river (Table
4.4).
Table 4.4: Distribution species of Eleotridae in Bassac river

No.
1
2
3
4
5

Scientific name
Eleotris melanosoma Bleeker, 1853
Oxyeleotris urophthalmus (Bleeker, 1851)
Oxyeleotris marmorata (Bleeker, 1852)
Butis butis (Hamilton, 1822)

Butis humeralis (Valenciennes, 1837)

Upstream

Middle

Downstream

++
+
+

++
++
+
+

++
++
+
+
+

(+): Number of species appear less (<30%); (++): Number of species appear more (30-60%) (Scheffer & Robinson, 1939)

Based on the frequency of occurrence of Scheffer and Robinson (1939) to
determine the dominant species occured in the upstream, middle and
downstream in Bassac river. Results showed that E. melanosoma appeared
more in three areas, O. urophthalmus appeared more in the middle and
downstream, O. marmorata, B. Butis and B. humeralis appeared less and

focused in middle and downstream. This results was similar to Le Ngoc
Dien (2011) and Tran Dac Dinh et al. (2013). According to Le Ngoc Dien
(2011), studied by traw net in the middle appeared only of E. melanosoma
and B. butis, while B. butis and B. humeralis occured in the downstream.
Results also showed that body length of E. melanosoma was smallest and
little changed between the rainy season and the dry season (Figure 4.9),
while the body length of O. marmorata was greatest and more fluctuation.
Moreover, the body length of E. melanosoma had several changes in the
12


upstream. Largest size of O. marmorata happened in the middle from April
to June (5.3 to 7.6 cm). According to Trinh Liet (2010), E. melanosoma and
O. urophthalmus appeared frequently at the beginning in rainy season from
May to June, this issue was similar to the statement of the fishermen.
20

Rainy season

Total length (cm/ind.)

18

Dry season

16
14
12
10
8

6
4
2
0
E. melanosoma O. urophthalmus O. marmorata

B. butis

B. humeralis

Scientific name

Figure 4.9: Length of five gobies appear in the rainy season and dry season

4.2.2 The abundance species of Eleotridae (CPUE)
The abundance species of Eleotridae (CPUE) was assessed 15 locations in
Bassac river in the upstream, middle and downstream. These locations were
showned in Table 4.5, Table 4.6 and Table 4.7.
Table 4.5: Coordinates of sampling locations in the upstream
Location
Rivers
Location 1 Main river (Long Binh wards , An Phu district)
Location 2 Main river (Khanh An wards , An Phu district)
Location 3 Main river (Binh Hoa wards, Long Xuyen city)
Location 4 Small river (Binh Hoa wards, Long Xuyen city)
Location 5 Smal river (Binh Hoa wards, Long Xuyen city)

Coordinates
: 10o56,221' N; : 105o04,278'E
: 10o56,277' N; : 105o06,734'E

: 10o33,025' N; : 105o18,724'E
: 10o28,767' N; : 105o20,417'E
: 10o28,113' N; : 105o20,531'E
In which:  is latitive,  is longitive, N is northern hemisphere, E is eastern hemisphere
Bảng 4.6: Coordinates of sampling locations in the middle
Nhánh sông
Coordinates
Location
Location 1

Main river (Thot Not wards, Thot Not district)

: 10o12,645' N; : 105o35,591'E

Location 2

Main river (Thot Not wards, Thot Not district)

: 10o11,971' N; : 105o35,696'E

Location 3

Main river (Cai Khe wards, Ninh Kieu district)

: 10o03,184' N; : 105o47,542'E

Location 4

Small river (Cai Khe wards, Ninh Kieu district)

: 10o00,456' N; : 105o44,838'E

Location 5

Small river (Phường Lê Bình, Quận Cái Răng)

: 10o00,467' N; : 105o45,537'E

In which:  is latitive,  is longitive, N is northern hemisphere, E is eastern hemisphere
Bảng 4.7: Coordinates of sampling locations in the downstream
Khu vực
Coordinates
Location
Main river (Dai Ngai town, Long Phu district)
: 09o44,206 'N; : 106o04,427'E
Location 1
Main river (Dai Ngai town, Long Phu district)
: 09o43,695' N; : 106o04,406'E
Location 2
Small river (Dai Ngai town, Long Phu district)
: 09o43,241' N; : 106o04,246'E
Location 3
Smal river (Tran De town, Tran De district)
: 09o31,646' N; : 106o12,139'E
Location 4
Main river (Tran De town, Tran De district)
: 09o30,144' N; : 106o12,838'E
Location 5
In which:  is latitive,  is longitive, N is northern hemisphere, E is eastern hemisphere

13


Surveys by traw net appeared only of E. melanosoma and B. butis, in
which, E. melanosoma appeared in the upstream and middle, while B. butis
appeared only in the downstream. CPUEn of E. melanosoma in dry season
ranged 1-173 ind./ha and was lower in rainy season (2-343 ind./ha), CPUEn
of the highest and fluctuated more in the upstream and middle (Figure
4.10); CPUEn of B. butis appeared only in the downstream very low
quantities, CPUEn of B. butis in dry season ranges from 1-21 ind./ha and
higher than in rainy season (3-6 ind./ha).
400

250

300

Dry season

Rainy season

50

Dry season

200

250

200

150
100
50

CPUEn (ind./ha)

Rainy season

CPUEn (ind./ha)

CPUEn (ind./ha)

350

150

100
50

1

2
3
Sampling sites

4

20

10

0

1

5

Dry season

30

0

0

Rainy season

40

2

3
4
Sampling sites

5

1

2

3
4
Sampling sites

5

Upstream
Middle
Downstream
Figure 4.10: CPUEn of Eleotris melanosoma and Butis butis in three areas surveyed

CPUEw of E. melanosoma in dry season ranged from 2.5 to 200.1 g/ha
lower than in rainy season (2.3 to 450.5 g/ha) and highest in the upstream
(Figure 4.10). Meanwhile, CPUEw of B. butis was from 2.6 to 89.7 g/ha and
higher than in rainy season (from 8.8 to 13.9 g/ha) (Figure 4.11). The
abundant of E. melanosoma in rainy season than more in dry season, in the
upstream more fluctuation in the middle, while species of B. butis appeared
in the downstream and it was less abundant compared to E. melanosoma,
this issue also similar to Trinh Liet (2010) and E. melanosoma appeared
more during in rainy season, especially when the floodwaters coming.
1000

1200
Dry season

Rainy season

400

Dry season

800

800
600
400
200

400
200
0

0
1

2

3
4
Sampling sites

5

Rainy season

300

600

CPUEw (g/ha)

Rainy season

CPUEw (g/ha)

CPUEw (g/ha)

1000

Dry season

200
100
0

1

2
3
4
Sampling sites

5

1

2

3
4

Sampling sites

5

Upstream
Middle
Downstream
Figure 4.11: CPUEw of Eleotris melanosoma and Butis butis in three areas surveyed

4.3 Study on nutritional characteristics of Eleotris melanosoma and
Oxyeleotris urophthalmus
4.3.1 Morphological and structure of the digestive organs
Species of E. melanosoma had upper mouth, mouth horizontal incision
stretching, mouth wide and stretching, the lower jaw was longer than the
upper jaw and mouth brought before. Teeth were often distributed in almost
two jaw bone and teeth sharp, smooth, lined up, mostly small teeth, pointy
oval lined up in most areas. The filtering gills agency and keep foods that
14


help protect the rear beam bearing, bearing comb short, slender, ranked
sparse and lined up on the supply carried toward the mouth cavity and it is
the group most carnivorous fish (Nguyen Bach Loan, 2003). Esophagus
after serial oropharyngeal cavity and tubular thick, short, thick walls, can
stretch by hand in many folds. Located next gastric esophageal tasked
fermentation container and digest food, thick-walled shaped short pockets,
pleats are more likely broadening, they usually have a relationship with
food and prey size. Intestine was the last part of the gastrointestinal tract is
responsible for secreting digestive enzymes and feed enzymes reception by
moving to other routes, plants also absorb nutrients into the blood, gut of E.

melanosoma has folded and short, indicating fish fond of animals. Also, the
width of the mouth in three groups with different sizes (Table 4.8), this
showed the E. melanosoma with choice of feed size according to the
process of development of fish.
Table 4.8: The width of the mouth of Eleotris melanosoma in three different sizes
Group
Number of samples
Total length (Lt, cm)
Width of the mouth (cm)
1
2
3

0.202±0.097a
0.539±0.139b
0.854±0.227c

2.5-5.0
5.1-7.0
7.1-9.0

64
88
97

The average value of a column with the same characters, the difference was not statistically significant (P> 0.05)

The relative length of the gut of E. melanosoma was also identified in three
size groups (from 0.68 to 0.71) (Table 4.9). According to Nikolsky (1963),
the species of fish were feeding the animals will be treated Li/Ls≤1,

omnivorous fish with Li/Ls=1-3 and herbivorous fish when Li/Ls≥3, this
results showed the feeding of E. melanosoma was animals.
Table 4.9: Index of Lt, Li, RLG of Eleotris melanosoma in three sizes

Targets
Lt
Li
Li/Lt (RLG)

Total length of fish (Lt, cm)
Lt=2,5-5,0
Lt=5,1-7,0
4.57±0.52
6.00±0.51
3.10±0.62
4.29±0.60
0.439±0.171
0.614±0.134

Lt=7,1-9,0
67.62±0.48
5.39±0.58
0.666±0.137

Lt: Total length (cm); Li: Length of the gut (cm)

O. urophthalmus had a wide mouth, upper, mouth downward, almost to the
mouth cavity, no mucus, characteristic stretching and feeding fish group
large size. Distributed on both sides of the tooth jaw, palate and pharynx,
teeth a lot, and most had sharp dog teeth grow in many types of goods in the

two upper and lower jaws. Gill rakers were composed by three double bows
bearing, each bearing with one double supply goods bearing combs (9-12
carries comb) located in the oropharyngeal cavity, white roses, piece, sir,
forming a line spiky form, located on the same network hardware and
instruction on oropharyngeal cavity. The esophagus was located next
15


oropharyngeal cavity, that brings food to the stomach. Tubular esophagus,
small and short, present in many folds, which showed high resilience is
carnivorous fish species. Fish stomach esophagus is followed, in sinus
introspection and feed storage function, providing enzymes involved in
digesting food, bag-shaped, large, thick-walled, present in many folds can
expand and accommodate large-sized prey. Short gastric, Y-shaped, thickwalled, many folds create high elasticity and can accommodate large food.
The results showed that oral widths differ in three size groups, in groups of
individuals with a total length (Lt) from 4.0 to 6.5 cm width mouth of O.
urophthalmus was 0.864±0.116 cm, in Lt=6.6 to 9.0 cm width mouth of O.
urophthalmus was 0.637±0.137 cm, in size from 9.1 to 12 cm width mouth
was 0.231±1.078 cm and also showed that this species likely food choices
and changes by an increase in the width of the mouth (Table 4:10).
Table 4.10: The width of the mouth of O. urophthalmus in three different sizes
Group
Total length (Lt, cm)
Width of the mouth (cm)
1
4.0-6.5
0.464±0.116a
2
6.6-9.0
0.637±0.137b

3
9.1-12.0
1.078±0.231c

Number of samples
27
71
155

The average value of a column with the same characters, the difference was not statistically significant (P> 0.05)

The RLG of O. urophthalmus was also analyzed in total length from 4 to 12
cm and RLG was defined as less than 1, ranged from 0.63±0.12 to
0.74±0.15 (Table 4:11).
Table 4.11: Index of Lt, Li, RLG of O. urophthalmus in three sizes
Total length of fish (Lt, cm)
Targets
Lt=4.0-6.5
Lt=6.6-9.0
Lt
5.85±0.58
8.04±0.75
Li
3.65±0.67
5.24±1.05
Li/Lt (RLG)
0.63±0.12
0.65±0.11
Lt: Total length (cm); Li: Length of the gut (cm)

Lt=9.1-12.5
9.95±0.64
7.29±1.40
0.74±0.15

4.3.2 Nutritional spectrum of E. melanosoma and O. urophthalmus
4.3.2.1 Indegredient of food acording to the frequency method
Indegredient of food of E. melanosoma including: crustaceans, molluscs,
small fish and other food (phytoplankton and zooplankton), in which
molluscs with 19.57%, crustaceans (8.70%) and juveniles (2,20%), while
other foods have a very high rate of 69.57% (Table 4.12).
Table 4.12: Indegredient of food of E. melanosoma acording to the frequency method
No.
Type of food
Number of sample (n=46)
Frequency (%)
1
Molluscs
9
19.57
2
Crustaceans
4
8.70
3
Juveniles
1
2.20
4
Other foods

32
69.57

Similar to species of E. melanosoma, composition of food consisted of four
groups. Meanwhile, crustacean appeared as 4.88%, molluscs (12.20%) and
juveniles (2.44%), while the other foods (phytoplankton and zooplankton)
16


have very high frequency (100%) (Table 4:13).
Table 4.13: Indegredient of food of O. urophthalmus acording to the frequency method
No.
Type of food
Number of sample (n=46)
Frequency (%)
1
Crustaceans
2
4.88
2
Molluscs
5
12.20
3
Juveniles
1
2.44
4
Other foods
41

100

4.3.2.2 Indegredient of food acording to the weigth method
Based on the weight of food in the stomach of E. melanosoma and
numerical analysis for each type of food were defined respectively:
molluscs: 70.16; Crustacean: 13.41; fry: 5.63 and others: 0.21 (Table 4:14).
Meanwhile, the weigth of each type of food in the stomach of O.
urophthalmus respectively: molluscs: 13.84; Crustacean: 17.57; fry: fry and
5.21: 0.25 (Table 4:15).
Table 4.14: Indegredient of food of E. melanosoma acording to the weigth method
No.
Frequency
Numerical
Type of foods
Weigth of food/stomach (g)
(%)
analysis
1
Molluscs
19.57
3.585
70.16
2
Crustaceans
8.70
1.541
13.41
3
Fingerlings
2.20

2.557
5.63
4
Others
69.57
0.003
0.21
Table 4.15: Indegredient of food of O. urophthalmus acording to the weigth method
No.
Weigth of food/stomach
Numerical
Type of foods
Frequency (%)
(g)
analysis
1
Molluscs
4.88
3.390
13.84
2
Crustaceans
12.20
1.722
17.57
3
Fingerlings
2.44
2.553
5.21

4
Others
100
0.003
0.25

Rate
(%)
78.5
15.0
6.3
0.2
Rate
(%)
37.5
47.7
14.1
0.7

In nutritional spectrum of E. melanosoma molluscs group has the highest
percentage (78.5%), crustaceans (15.0%), juveniles (6.3%) and other foods
(0.2%); whereas of O. urophthalmus was crustaceans group with the
highest percentage (47.7%, molluscs (37.5%), juveniles (14.1%) and other
foods (0.7%) (Figure 4.12). According to Watts (2004), favorite food was
small fish, molluscs and crustaceans, and according to Le Thi Ngoc Thanh
(2010), crustaceans and small fish has about 30% of O. urophthalmus.
Crustaceans
(15.0%)

Fingerlings

(6.3%)

Fingerlings
(14.1%)

Others
(0.2%)

Others (0.7%)
Molluscs
(37.5%)

Molluscs
(78.5%)

Crustaceans
(47.7%)

Eleotris melanosoma
Oxyeleotris urophthalmus
Figure 4.12: Nutritional spectrum of E. melanosoma and O. urophthalmus

17


4.4 Study on reproductive biology of Eleotris melanosoma and
Oxyeleotris urophthalmus
4.4.1 The sexual maturity of E. melanosoma and O. urophthalmus
4.4.1.1 Stages of the sexual maturity
Rate of sexual maturity of E. melanosoma was different in months. Stage I

and II differred from January to March and from July to September, rate of
sexual maturity maximum from October to December (68-82%) (Figure
4.13), stage IV appeared throughout the year and the highest since April to
June (50%). According to Nguyen Kim (2012), the E. melanosoma eggs
appeared much from March to June and October to December and female
gonads highest stage IV in May and June (50%). The results showed that
breeding season of E. melanosoma focused in rainy season, starting in May
and ending in October, focusing on May to July.
The stages of sexual maturity of O. urophthalmus varied over time. In stage
I and II appeared from December to Febuary (Figure 4.12), stage IV also
appeared throughout the year and the highest from May to June (45%),
which showed that breeding season of O. urophthalmus was whole year and
concentrate from April to June, they usually appear in the flood season
(from August to October) and this time is the main crop appearance their
(Hajisamae, 2006).
Stage III

Stage IV

Stage I và II
100

90

90

80

80

70

70
Percentage ( %)

Percentage ( %)

Stage IV
100

60
50
40

30

Stage III

Stage I và II

60
50
40

30
20

20

10

10

0

0

8/2012 9/2012 10/2012 11/2012 12/2012 1/2013 2/2013 3/2013 4/2013 5/2013 6/2013 7/2013

8/2012 9/2012 10/2012 11/2012 12/2012 1/2013 2/2013 3/2013 4/2013 5/2013 6/2013 7/2013

Month

Month

Eleotris melanosoma
Oxyeleotris urophthalmus
Figure 4.13: Percentage (%) stages of sexual maturity of E. melanosoma and O. urophthalmus

4.4.1.2 Stages of the ovary development of E. melanosoma and O.
urophthalmus
Stages of the ovary development were determined up to stage IV (Nikolsky,
1963). Observed with the eyes in stage I and II were difficult to identify,
when the matured to stage III and IV easily identifiable and this time the
surface of the ovary appear small blood vessels, the color begins moving
from bright yellow to pale yellow (Figure 4.14).

18

Stage I of the ovary

Stage II of the ovary

Stage III of the ovary

Stage IV of the ovary

Stage I of the ovary

Stage III of the ovary

Stage II of the ovary

Stage IV of the ovary

Eleotris melanosoma
Oxyeleotris urophthalmus
Figure 4.14: Morphology of the ovary development stage of E. melanosoma and O. urophthalmus

The development ovary stages of E. melanosoma and O. urophthalmus was
also determined by histological methods. Their gonads stage I easily
observed on whole cell slice ovum, the big round, with a larger percentage
volume stage II oocytes. Size of stage II oocytes increases, and the cell's
rate reduction, sharp particles of hematoxylin purple emulsion. Stage III
switch to oocyte growth nutrients, oocytes begin the accumulation stage,
there was many vacuoles appear unstained, the big catch light purple, size
increase oocyte, cytoplasmic popularity but weak alkaline, yolk appears
more pink eosin. Stage IV oocytes size increases, the number of nodes in
human urine decreased and disappear into human services, the size maxima

oocytes, cell nucleus has no fixed shape (Figure 4.15).
Tissue sample at objective
lens x10.
: Natural ovum cell:
ratio of cell nucleus > cells,
cytoplasmic staining of
Haematoxylin
: Oocyte: size
increases, the ratio between
nuclear and cell reduced,
emulsion particles purple
color of hematoxylin

Tissue sample at objective
lens x10.
: Natural ovum cell:
ratio of cell nucleus > cells,
cytoplasmic staining of
Haematoxylin
: Oocyte: size
increases, the ratio between
nuclear and cell reduced,
emulsion particles purple
color of hematoxylin

Phase I of the ovary

Phase I of the ovary

Phase II of the ovary

Phase II of the ovary

Tissue sample at objective
lens x10.

Tissue sample at objective
lens x10.

: Vacuoles are
interspersed in the yolk
: Cell nucleus
: Yolk particles

Phase III of the ovary

: Vacuoles are
interspersed in the yolk
: Cell nucleus
: Yolk particles

Phase III of the ovary

Phase IV of the ovary

Phase II of the ovary

Eleotris melanosoma
Oxyeleotris urophthalmus
Figure 4.15: Tissue sample stages gonad development of E. melanosoma and O. urophthalmus

4.4.1.3 Stages of the spermatorrhoea development of E. melanosoma and O.
urophthalmus
Morphology of E. melanosoma and O. urophthalmus based on Nikolsky
(1963) include: spermatorrhoea immature stage and mature spermatorrhoea
stage: (i) Stage of spermatorrhoea immature: spermatorrhoea shape fiber,
stool small lobes, located hugging the fish spine, observed with the naked
19


eyes is difficult to determine the stage of development of spermatorrhoea,
and (ii) Stage of mature spermatorrhoea: spermatorrhoea expand and
increase size, surface tension spermatorrhoea bulging and rounded,
observed with the naked eye can see inside the sperm contains milky.

Spermatorrhoea stage of immature

Spermatorrhoea stage of mature

Spermatorrhoea stage of immature

Spermatorrhoea stage of mature

Eleotris melanosoma
Oxyeleotris urophthalmus
Figure 4.16: Spermatorrhoea of E. melanosoma and O. urophthalmus immature and mature stages

The development stages of E. melanosoma and O. urophthalmus was also
determined by histological methods. In stage spermatorrhoea appear
immature reproductive cells early stages of the process of creating crystal,

crystal cell level 1, level 2 and sperm. Meanwhile, stage of spermatorrhoea
mature only mature sperm come out of cysts, large gonialblast and ends the
process of creating crystal (Figure 4:17).
Tissue sample at objective
lens x40.
: Gonialblast, cytoplasmic
staining of Eosin pinkis
: Crystalline cells of primary
: Crystalline cells of
secondary
: Spermatid
The sperm cells of primary,
secondary and spermatid have
purple blue of Heamatoxylin

Eleotris melanosoma
Oxyeleotris urophthalmus
Figure 4.17: Tissue sample stages spermatorrhoea development of E. melanosoma and O. urophthalmus

4.4.2 Gonadosomatic index and hepatosomatic index
Gonadosomatic index (GSI) and hepatosomatic index (HSI) of E.
melanosoma and O. urophthalmus determined from August 2012 to July
2013. Results showed that GSI and HSI of E. melanosoma fluctuate more
males and females from August to October (Figure 4.18 and Figure 4.19).
The highest from May to October and HSI lowest in July, conditional factor
(CF) was highest in April and November (Figure 4.18). Meanwhile, GSI of
O. urophthalmus more than HSI (from June to October), GSI of males from
0.14% to 1.71% and females from 1.59% to 9.70% (Figure 4:18 and Figure
4.19). HSI of O. urophthalmus from 0.26% to 2.06% (in male) and from
0.74% to 7.58% (in females) (Figure 4.19). According to Pham Thanh Liem

and Tran Dac Dinh (2004), sexual maturity factor and accumulated energy
systems of fish were an important factor to predict spawning season and
was mainly based on gonad fish to determine.
20


14

14

Male

Female

Male

10

GSI (%)

12

10

GSI (%)

12

8

Female

8

6

6

4

4

2

2
0

0

8/2012 9/2012 10/2012 11/2012 12/2012 1/2013 2/2013 3/2013 4/2013 5/2013 6/2013 7/2013

8/2012 9/2012 10/2012 11/2012 12/2012 1/2013 2/2013 3/2013 4/2013 5/2013 6/2013 7/2013

Month

Month

Eleotris melanosoma
Oxyeleotris urophthalmus
Figure 4.18: GSI of E. melanosoma and O. urophthalmus

14

14
Male

Female

Male

12

10

10

8

8

HSI (%)

HSI (%)

12

6
4

Female

6
4

2

2
0
8/2012 9/2012 10/2012 11/2012 12/2012 1/2013 2/2013 3/2013 4/2013 5/2013 6/2013 7/2013

0
8/2012 9/2012 10/2012 11/2012 12/2012 1/2013 2/2013 3/2013 4/2013 5/2013 6/2013 7/2013

Month

Month

Eleotris melanosoma
Oxyeleotris urophthalmus
Figure 4.19: HSI of E. melanosoma and O. urophthalmus

4.4.3 Conditional factor (CF)
CF of male E. melanosoma was highest in April and November (CF=0.04)
and smallest in December (CF=0.01), CF of O. urophthalmus was highest
CF 0.03 (females) and lowest was 0.01. CF was determined by the
coefficient of correlation between the length and weigth of them and assess
the level of increase in the weigth of gobies than the length (King, 1995).
0.055
0.055

Female

Male

Female

0.050

Male

0.050

0.045

0.045

0.040

0.040

0.035

CF (g/cm)

CF (g/cm)

0.035
0.030

0.025
0.020

0.030
0.025
0.020

0.015

0.015

0.010

0.010

0.005

0.005

0.000
8/2012

9/2012 10/2012 11/2012 12/2012 1/2013

Month

2/2013

3/2013

4/2013

5/2013

6/2013

7/2013

0.000
8/2012

9/2012 10/2012 11/2012 12/2012 1/2013

2/2013

3/2013

4/2013

5/2013

6/2013

7/2013

Month

Eleotris melanosoma
Oxyeleotris urophthalmus
Figure 4.20: CF of E. melanosoma and O. urophthalmus

4.4.4 Rate of male and female

By analyzing 125 samples of E. melanosoma showed that having 45 males,
64 females and 16 samples were not to determine the gender. Percentage of
male E. melanosoma accounted for 41% lower females (59%). Similarly,
species of O. urophthalmus analyzed 106 samples and 47 samples females
(60%), 31 samples males (40%) and 28 samples were not to determine the
gender. However, by statistical analysis (χ2, 109 samples of E. melanosoma
and 78 samples of O. urophthalmus) showed that the male and female ratio
observed in experimental conditions was no difference statistically
21


significant compared to rates expect (1:1).
4.4.5 Fecundity of E. melanosoma and O. urophthalmus
Fecundity of E. melanosoma and O. urophthalmus were determined based
on ovaries developed stage IV. Fecundity of E. melanosoma was 551±363
eggs/g females in length of 7.2±1.2 cm/ind., weight was 5.26±2.97 g/ind.
Fecundity of O. urophthalmus was 187±134 eggs/g females, lower compare
to E. melanosoma (44-477 eggs/g females) in body length was 10.1±1.5
cm/ind. and 12.31±6.14 g/females. Compared with Fouda (1993), fecundity
of them similar to red goby (152-782 eggs/g females) and lower compare to
some gobies living in the Mediterranean (293-1,300 eggs/g females) with
weigth of 603 eggs/g females.
4.4.6 Mature length of E. melanosoma and O. urophthalmus
By analyzing 139 samples males and 99 females samples of E. melanosoma
showed the maturity length (Lm) was 8.62 cm (in males) and 7.79 cm (in
females) (Figure 4.21). Meanwhile, Lm of O. urophthalmus larger than E.
melanosome, little difference between males and females in the same
populations, Lm of O. urophthalmus was Lt=11.36 cm (in male) and
Lt=7.97 cm (in female) (Figure 4.22). According to King (1995), father of
the length at which gobies populations have 50% of individuals in the

colony had grown to maturity stage (stage III).
1.0

1.0

L: Total length (cm)
P: Maturation rate reached 50%
of goby stocks
P: tỉ lệ cá thành thục đạt đến
L: chiều dài toàn thân cá (cm)

0.8

P: tỉ lệ cá thành thục đạt đến
50% trong quần đàn

0.8

50% trong quần đàn

0.7

trịtrịPP
of PGiá
ValueGiá

0.7

0.6

-0,532356*(L-8,62496)

P=1/{1+e

0.5

}

R=0,961
n=139

0.4

P

0.6

P

L:L:Total
Totallength
length(cm)
(cm)
P:P:Maturation
Maturationrate
ratereached
reached50%
50%
ofofgoby
gobystocks

stocks

L: chiều dài toàn thân cá (cm)

0.9

trịtrịPP
Giá
ofPPGiá
Value
Valueof

0.9

-0,532356*(L-8,62496)

P=1/{1+e

0.5

}

R=0,961
n=139

0.4
0.3

0.3

0.2

0.2
0.1

0.1
0.0

0.0

2

2

3

4

5

6

7

8

9

10

Giá
trị of
L L
Value

11

12

13

14

15

16

3

4

5

6

7

8

9

10

Giá
trị of
L L
Value

17

11

12

13

14

15

16

17

Value
of L
L

L

Male

Female
Figure 4.21: Mature length of E. melanosoma

1.0

L: Total length (cm)
P: Maturation rate reached 50%
of goby
stocks
-0,335283*(L-(11,3551)
P=1/{1+e
}
R=0,953
n=180

P

0.6
0.5
0.4

of P
Value
trị
Giá
Giá
trị PP

0.7

1.0 1.0

L:L:Total
(cm)
chiều
dàilength
toàn
dài toàn
thân
thân
cá (cm)
cá (cm)
0.9 0.9 L: chiều

P: Maturation rate reached 50%

0.8 0.8

P:of
tỉP:
lệ
tỉcálệthành
cá
thành
thụcthục
đạt đến
đạt đến
goby

stocks
50%50%
trong
trong
quầnquần
đàn đàn

0.7 0.7

L: chiều dài toàn thân cá (cm)

0.6 0.6

P: tỉ lệ cá thành thục đạt đến
50% trong quần đàn

0.5 0.5

P

0.8

Giá
Giá trị
trị PP
P of PP
Value
Giá
Giá trị
trị P

0.9

0,3865*(L-(7,96827
0,3865*(L-(7,96827
)
)

P= 1/{1+e
P= 1/{1+e
R=0,955
R=0,955
n=286
n=286

0.4 0.4

0.3
0.3 0.3

}

}

0.2
0.2 0.2

0.1
0.1 0.1

0.0
1

2

3

4

5

6

7

8

9

10

11

Male

12

13

Giá trịofL L

Value
L

14

15

16

17

18

19

20

0.0 0.0
0 0

2

2

4

4

6

6

8 Giá
10L
10L
Giá
trị
trị
Value
of
L

8

L

12 12

14 14

16 16

18 18

20 20

L

Female
Figure 4.22: Mature length of O. urophthalmus

CHAPTER 5: CONCLUSION AND RECOMMENDATION
5.1 Conclusion
In Bassac river, values of pH ranged from 7.0 to 8.5; temperature: 27-33oC;
22


salinity in the downstream appeared in February, June and December, the
lowest in rainy season (0-7.6‰) highest dry season (2-10.8‰), the water
flow in rainy season higher dry season (0.1-1.3 km/hour), the depth in the
middle higher upstream and downstream (4.3-14.4 m).
Structure of aquatics in the upstream and middle was higher than that in the
downstream. The phytoplankton in the upstream has 31 species, middle had
22 species and downstream has 15 species, Bacillariophyta was dominated.
The zooplankton in the upstream had 33 species, middle had 35 species and
downstream had 68 species, in which protozoa was dominated. The
zoobenthos in the upstream had 17 species, middle had 23 species and
downstream had 17 species, gastropoda was dominated.
There were five species of Eleotridae living in Bassac river including:
Eleotris melanosoma, Oxyeleotris urophthalmus, Oxyeleotris marmorata
often appear in the upstream, middle and downstream, while species of
Butis Butis appeared in the middle and downstream and species of Butis
humeralis appeared only in the downstream. However, when we catch by
trawl species of E. melanosoma had in the upstream and downstream, while
species of Butis butis appeared only in the downstream and the abundant in
rainy sean higher in dry season.
Species of E. melanosoma and O. urophthalmus had intestinal length
shorter body length, feeding habits of their was animals. Their food
spectrum relatively, including: crustaceans (78.5%; 37.5%), molluscs
(15.0%; 47.7%), juveniles (6.3%; 14.1%) and other foods (0.2%; 0.7%).

Gonadosomatic index of E. melanosoma and O. urophthalmus was high
from May to October and hematosomatic index of their was lowest in July,
conditional factor was highest in April and November. Their breeding was
season from May to October, focused from May to July. Absolute fecundity
of E. melanosoma was 2,981-19,520 eggs/female; O. urophthalmus ranged
1,290-9,999/female, relative fecundity E. melanosoma was 49-930 eggs/g
female higher than O. urophthalmus (44-477 eggs/g female). Length of
mature (Lm) of E. melanosoma was 8.62 cm (male) and 7.79 cm (female);
while Lm of O. urophthalmus was 11.36 cm (male) and 7.96 cm (female).
5.2 Recommendation
Study on artificial reproductive of Eleotris melanosoma and Oxyeleotris
urophthalmus was able to develop into farmed.
Study on ability of salt tolerance and some biological characteristics of
Butis humeralis was able to develop into the cultured species, contributing
to diversification of cultured species in coastal areas and adaptation to
climate change.
23