study on reproductive biology of vermiculated sailfin catfish (pterygoplichthus disjunctivus weber, 1991) in can tho and đong thap provinces

CAN THO UNIVERSITY COLLEGE OF AQUACULTURE AND FISHERIES STUDY ON REPRODUCTIVE BIOLOGY OF VERMICULATED SAILFIN CATFISH Pterygoplichthys disjunctivus Weber, 1991 IN CAN THO AND ĐONG THAP

CAN THO UNIVERSITY COLLEGE OF AQUACULTURE AND FISHERIES

STUDY ON REPRODUCTIVE BIOLOGY OF VERMICULATED

SAILFIN CATFISH (Pterygoplichthus disjunctivus Weber, 1991) IN

CAN THO AND ĐONG THAP PROVINCES

By NGUYEN KIM CUONG

A thesis submitted in partial fulfillment of the requirements for

the degree of Bachelor of Aquaculture Science

Can Tho, December 2013

CAN THO UNIVERSITY COLLEGE OF AQUACULTURE AND FISHERIES

STUDY ON REPRODUCTIVE BIOLOGY OF VERMICULATED

SAILFIN CATFISH (Pterygoplichthys disjunctivus Weber, 1991) IN

CAN THO AND ĐONG THAP PROVINCES

By NGUYEN KIM CUONG

A thesis submitted in partial fulfillment of the requirements for

the degree of Bachelor of Aquaculture Science

Supervisor Assoc Prof Dr TRAN DAC DINH

Can Tho, December 2013

APPROVEMENT

The thesis “Study on reproductive biology of vermiculated sailfin catfish

(Pterygoplichthys disjunctivus Weber, 1991) in Can Tho and Dong Thap

provinces” defended by Nguyen Kim Cuong, which was edited and passed by

committee on 12-27-2013

Sign of Supervisor Sign of Student

Assoc Prof Dr Tran Dac Dinh Nguyen Kim Cuong

ACKNOWLEDGEMENT

My special thanks are given to Assoc Prof Dr Tran Dac Dinh for his constant guidance and useful advices that helped me to conduct and complete this thesis

Thanks to the teaching staffs in department of fisheries management and economics, College of Aquaculture and Fisheries – Can Tho University and students of Advanced Aquaculture Program Class Course 2nd for enthusiasm help during the period of sampling and data analysis

Thanks to Miss Ho Thi Thuy Huong and Nguyen Thi Vang help me during the period of experimentation and data analysis

Finally, I would like to thank to my family and friends helped and made the best conditions for me during my study of bachelor program in aquaculture

Nguyen Kim Cuong

ABTRACT

This thesis studied on reproductive biology of vermiculated sailfin catfish

(Pterygoplichthys disjunctivus,Weber 1991) in Can Tho and Dong Thap provinces

from July to October in 2013 The results indicated that length-weight relationships were very close with high R2, including total length-weight relationship equation W=0.0115L2.8967 with R2 = 0.9759 (n=216) and standard length-weight relationship equation W=0.0759L2.5647 with R2 = 0.9485 (n=216) Besides, condition factor (CF)

of males was the highest in September (0.0119) and the lowest was in October (0.0111), CF of females was the highest in October (0.0119) and the lowest CF was

in August (0.0112) Next, maturity proportion was the highest in July (90%) and the lowest was in September (69.61%),most of males were mature in July and August (more than 70% ) and the females were mature in 4 months from July to October (more than 90%), sex proportion were 93 females (43.06% ), 123 males (56.94% ) and sex ratio ( female: male) was 1 : 1.32 In addition, Gonadosomatic index (GSI)

of males was the highest in August (0.6175%) and the lowest was in October (0.0659%), GSI of females were very high (5.5246% -8.3018%), the highest was in October (8.3018%) and the lowest was in August (5.5246%) Hepatosomatic index (HSI) of males was the highest in August (1.1195%) and the lowest was in October (0.8378%), HSI of females also was the highest in August (1.2109%) and the lowest

was in October (0.8388%) Average of fecundity of Pterygoplichthyus disjuntivuswas 2002 eggs/female (324 – 6621 eggs/female), average of relative

fecundity was 13 eggs/gram of female (4 – 23 eggs/gram of female) The fecundity

of fish was not stable because Pterygoplichthyus disjunctivus reproduced many time per year Fecundity – weight relationship of Pterygoplichthyus disjuntivuswas

indicated by equation F = 16.203W0.9456 with R2= 0.836.Finally, total length at first maturity was indicated by equation y = -0.639x + 9.926 with R2 = 0.842, the result

of total length at first maturity was 15.53 cm

TABLE OF CONTENT

Acknowledgements i

Abstract iii

TABLE OF CONTENT iv

LIST OF TABLES vi

List of figures vii

LIST OF ABBREVIATIONS viii

CHAPTER I 1

INTRODUCTION 1

1 Background of the research 1

2 Research objective 2

3 Research contents 3

CHAPTER II 4

LITERATURE 4

1 Overview of natural condition, aquaculture and fisheries in Can Tho 4

2.Overview of natural condition, aquaculture and fisheries in Dong Thap 5

3 Classification, morphological characteristics and distribution of Pterygoplichthyus disjunctivus (Weber, 1991) 7

4 Nutritional characteristics 8

5 Growth characteristics 8

6.Reproduction characteristics 9

7 Environmental impacts 10

CHAPTER III 12

MATERIALS AND METHODOLOGY 12

1 Materials 13

2 Methodology 13

2.1 Sampling and fixing samples 13

2.2 Criteria for sample analysis 13

2.3 Length-weight relationship and condition factor (CF) 13

2.4 Maturity stages, maturity proportion and sex ratio 14

2.5 Gonadosomatic Index (GSI) 15

2.6 Hepatosomatic Index (HSI) 16

2.7 Fecundity 16

2.8 Total length at first maturity (Lm) 17

2.9 Data analysis method 17

CHAPTER IV 18

RESULTS AND DISCUSSIONS 18

1 Morphological criteria and characteristics 18

2 Length – weight relationship and condition factor (CF) 20

2.1 Total length – weight relationship 20

2.2 Standard length – weight relationship 20

2.3 Condition factor (CF) 22

3 Maturity stages, maturity proportion and sex ratio 23

3.1 Maturity proportion and maturity stages 23

3.2 Sex ratio 25

4 Gonadosomatic index (GSI) 26

6 Fecundity 29

7 Total length at first maturity 31

CHAPTER V 32

CONCLUSIONS AND RECOMMENDATIONS 32

1.Conclusions 32

1.1 Length-weight relationship and condition factor 32

1.2 Gonadosomatic index (GSI) 32

1.3 Hepatosomatic index (HSI) 33

1.4 Fecundity 33

1.5 Total Length at first maturity 33

2 Recommendations 33

REFERENCE 34

APPENDIX 36

LIST OF TABLES

Table 1: Description of Maturity stages (Nikolsky 1963) 15

Table 2: Comparison of morphological criteria between Pterygoplichthyus disjunctivus (Weber, 1991) with other researchs 18

Table 3:Propotion of morphological criteria of Pterygoplichthyus disjunctivus 18

Table 4: Condition factor (CF) of Pterygoplichthyus disjunctivus (males) 22

Table 5: Condition factor (CF) of Pterygoplichthyus disjunctivus (females) 22

Table 6: Maturity proportion (%) of Pterygoplichthyus disjunctivus 23

Table 7: Sex proportion (%) and sex ratio of Pterygoplichthyus disjunctivus in every month 26

Table 8: Gonadosomatic index of Pterygoplichthyus disjunctivus (males) 26

Table 9: Gonadosomatic index of Pterygoplichthyus disjunctivus (females) 27

Table 10: Hepatosomatic index of Pterygoplichthyus disjunctivus (males) 28

Table 11: Hepatosomatic index of Pterygoplichthyus disjunctivus (females) 29

Table 12: Determination of total length at first maturity of Pterygoplichthyus disjunctivus 31

LIST OF FIGURES

Figure 1: Vermiculated sailfin catfish (Pterygoplichthys disjunctivus Weber,1991) 1

Figure 2: Sampling area in Can Tho 12

Figure 3: Sampling area in Dong Thap 12

Figure 4: Vermiculated sailfin catfish (Pterygoplichthyus disjunctivus Weber, 1991) 19

Figure 5: Sucker mouth of Vermiculated sailfin catfish (Pterygoplichthyus disjunctivus Weber, 1991) 19

Figure 6: Total length – weight relationship of Pterygoplichthyus disjunctivus 20

Figure 7: Standard length–weight relationship of Pterygoplichthyus disjunctivus 21

Figure 8: Condition factor (CF) of Pterygoplichthyus disjunctivus (males) 22

Figure 9: Condition factor (CF) of Pterygoplichthyus disjunctivus (females) 23

Figure 10: Maturity stages proportion (%) of males 24

Figure 11: Maturity stages Proportion (%) of females 25

Figure 12: Sex proportion of Pterygoplichthyus disjunctivus in 4 months 25

Figure 13: Gonadosomatic index of pterygoplichthyus disjunctivus (males) 26

Figure 14: Gonadosomatic index of Pterygoplichthyus disjunctivus (females) 27

Figure 15: Hepatosomatic index of Pterygoplichthyus disjunctivus (males) 28

Figure 16: Hepatosomatic index of Pterygoplichthyus disjunctivus (females) 29

Figure 17: Fecundity – weight relationship of Pterygoplichthyus disjunctivus 30

Figure 18: Total lenght at first maturity of Pterygoplichthyus disjunctivus 31

GSI Gonadosomatic index

HIS Hepatosomatic index

F Fecundity

Lm Total length at first maturity

n Amount of samples

G Weight of the ovaries

g Weight of the sub-sample

P Maturity proportion

WL Weight of liver

GW Gonad weight

BW Body weight

CHAPTER I INTRODUCTION

1 Background of the research

Vermiculated sailfin catfish (Pterygoplichthys disjunctivus Weber,

1991) distributed in the North and Central America, Asia, Caribbean area and Hawaii It invaded many states, including Florida, Texas, and especially Hawaii, it was nonnative and harmful specie It can live in relatively cool, fast-flowing and oxygen-rich highland streams to slow-flowing, warm lowland rivers and oxygen- poorstagnant pools Besides, it also has wide amplitude of temperature, although be a tropical specie but it can service in cold areas in the Winter It is also highly tolerant to poor water quality and is commonly found

in polluted waters Specially, Vermiculated sailfin catfish can move on land at

a certain distance It is omnivore but main foods are algae and seaweed on the bottom or surface of aquatic plants Abundance of Vermiculated sailfin catfish

is the cause of declining some native aquatic species because it not only vies food but also eats eggs of other species, controlling is very difficult if it invades with high density

Figure 1: Vermiculated sailfin catfish (Pterygoplichthys

disjunctivusWeber,1991)

In Viet Nam, special concern is development of vermiculated sailfin catfish with high density in wetlands natural conserves such as Tram Chim, U Minh Thuong, Lang Sen, Tan Hung, Lung Ngoc Hoang and rivers, channels, canals, lakes,… in Mekong Delta leads to disturbance ecosystems and biological imbalance

In Me Kong Delta, the people worry so much about vermiculated sailfin catfish, it not only lives in rivers, ponds, lakes, channels…but also lives

in ponds for aquaculture, potential effects of them include alteration of bank structure and erosion, disruption of aquatic food chains, competition with native species, mortality of endangered shore birds, changes in aquatic plant communities and damage to fishing gear and industry

Some provinces have high density of vermiculated sailfin catfish are Can Tho, An Giang, Dong Thap, Soc Trang, Vinh Long, Tra Vinh, specially is

in Can Tho and Dong Thap Controlling can be done easily in ponds for aquaculture by draining and cleaning ponds but it is very difficult to do in natural conserves

Researches about species composition, biological characteristics, growth characteristics, its impacts on the ecosystem, competition with other species, its regions of residence, fertility, measures to control…of vermiculated sailfin catfish need to be done to have accurate appraisal and effective methods for management, protection and development aquatic resources So topic “study on reproductive biology of the vermiculated sailfin catfish in Can Tho and Dong Thap provinces ” is very necessary

2 Research objective

To find out some reproductive biological characteristics of

vermiculated sailfin catfish (Pterygoplichthys disjunctives Weber 1991)

distributed in Can Tho and Dong Thap provinces to provide data for management reproduction of vermiculated sailfin catfish and protection, development of native aquatic species

3 Research contents

To study some reproductive biological characteristics such as: weight relationship, condition factor (CF), sex ratio, stages of maturity, maturity proportion, gonadosomatic index (GSI), hepatosomatic index (HSI),

length-total length at first maturity and fecundity

CHAPTER II LITERATURE

1 Overview of natural condition in Can Tho

Can Tho is directly under the Central authorities, lies in the heart of the Mekong River Delta, bordered by An Giang and Dong Thap in the north, Vinh Long in the East , Hau Giang in the South and Kien Giang in the West Being dubbed as “the capital city of the Southwestern Vietnam” more than one hundred years ago, Can Tho became the level 1 city and one of the four provinces and cities of the Mekong River Delta Key Economic Zone–the fourth key economic zone of Vietnam Can Tho not only has favorable natural conditions and geographical position to develop agriculture, fishery but also develop others such as urban infrastructure, traffic infrastructure, hi-tech agriculture, agricultural aquatic products and seafood processing industry, tourism and supportive industries

Area: 1,389.60 km2

Population: 1.2 million people (2012)

Population density: 856 people/ km2 (2012)

Climate: Can Tho belongs to the tropics with two distinct seasons: the

rainy season is from May to November, and the dry season is from December

to April The annual average temperature was 270C; the annual average rainfall was 1,635 mm; the annual average humidity was 83% There are two main wind direction, northeast wind (dry season) and southwest wind ( rain season), average wind speed was 1.8 m/s, few storms but it will be in rain season

Topography: Can Tho has relatively flat terrain, average height is

about 1 – 2 m, It is convenient for agriculture and fishery production Can Tho lies in the half-flooded plains that were gradually sloping from northeast to southwest, including three kinds of terrain: natural dikes alongside Hau River (forming the strip of high land and islands along Hau River); half-flooded

plains (belonging to the Long Xuyen Tetragon that is directly influenced by the flood every year); delta plains (mainly influenced by the tide and some interactive influences from the crop-end floods)

Hydrology: Can Tho had dense river, channel, canal system and many

islets on Hau river Hau river is the biggest river with total length run through Can Tho is about 65km and the width is about 1.6 km, total water quantity flow to the sea was about 200 billions m3/year (make up about 41% of total water volume of Me Kong river), total alluvium was about 35 millions m3/year (near ½ total alluvium of Me Kong river) Can Tho river is from the West of Hau river with 16 km in length and 280-350 m, flow through O Mon, Phong Dien, Cai Rang, Ninh Kieu provinces, it has freshwater year round which help for irrigation in dry season, drainage in rain season and transportation Besides, there are many other rivers and channel such as Thot Not, Vinh Thanh, Co Do, Phong Dien that help for soil improvement, irrigation, breeding, cultivation…

Administrative organization: Can Tho City has 9 administrative units

including 5 urban districts of Ninh Kieu, Binh Thuy, Cai Rang, O Mon, Thot Not and four suburban districts of Phong Dien, Co Do, Thoi Lai, Vinh Thanh with 5 towns, 44 wards and 36 communes (statistical data from the time of issuing the Decree 12/ND-CP)

2.Overview of natural condition in Dong Thap

Dong Thap is a province in the Mekong Delta region of southern Vietnam, bordered by Pray Veng province (Cambodia) in the North with a length of more than 48km, Vinh Long and Can Tho in the South, An Giang in the West and Long An and Tien Giang in the East Dong Thap has many advantages to develop agriculture, aquaculture, agricultural aquatic products and seafood processing industry, tourism and supportive industries

Area: 3,376.4km2(2011)

Population: 1.673.200 (2011)

Topography: quite flat with a sloping tendency from North to South

and West to East; separating into two large regions: one is in the North of Tien River (having an area of 250,731ha, in Dong Thap Muoi area) and one is in the South of Tien River (having an area of 73,074 ha, lying between Tien River and Hau River) Dong Thap has benefits from a large river, channel and spring system, frequently silt-aggraded soil, permanently fresh and non-saline water source

Climate: Dong Thap is in the tropical climate zone, consistently in the

whole province There are two evident seasons; rainy season from May to November, and dried season from December to April of the following year Average rainfall ranged from 1,682-2,005mm, mostly in rainy season, which accounted for 90-95% of annual rainfall Such climate was advantageous for agricultural development The average temperature was 27 0C, of which the highest was 34.3 0C, and the lowest was 21.8 0C

Hydrology: under the influence of three factors: floodwater from upper

Mekong River, in-field rain and tides of the South East Asia Sea The hydrologic regime is divided into 2 seasons: exhausted season from December

to June of the following year and flood season from July to November Dong Thap has abundant surface water, fresh water year round, two rivers branch are So Ha river and So Thuong river from Cambodia flew to Tien river in Hong Ngu, there are also many rivers in the South such as Cai Tau Ha, Cai Tau Thuong, Sa Dec….Specially, Dong Thap also has underground water reservoir with different depth

Administrative organization: With an area of 3,374km2, Dong Thap is

divided into twelve administrative regions: one provincial city (Cao Lanh), two towns (Sa Dec and Hong Ngu) and nine districts (Cao Lanh, ThapMuoi, Thanh Binh, Tam Nong, Tan Hong, Hong Ngu, Chau Thanh, Lai Vung and Lap Vo)

3 Classification, morphological characteristics and distribution

ofPterygoplichthyus disjunctivus (Weber, 1991)

Scientific name: Pterygoplichthyus disjunctivus (Weber, 1991)

English name: Vermiculated sailfin catfish

Vietnamese name: cálaukiếng

Loricariiadae family has about 80 genera and over 700 species, Loricariidae isthe largest family of catfishes (Siluriformes) (Armbruster and Page, 2006) Loricariids areendemic to South America (absent in Chile), Panama, and CostaRica, they are characterized by having large bony plates and a ventral sucker mouth with or without noticeable barbells, we can find them from lowland to upland depend on characteristics of every specie, their

body size can be from some centimeter up to 1 meter (Fuller, 1999)

Most of Pterygoplichthys disjunctivus distribute in the North and

Central America, Asia, Caribbean area and Hawaii Especially in the South of

US such as Florida, Texas and Mexico (Wakida-Kusunokiet al, 2007)

Besides, they also distribute in Oahu island (Hawaii)(Yamamoto and Tagawa,

2000), Puerto Rico (Bunkley-Williams et al, 1994) and Jamica In Asia, they

distribute in many countries such as Singapore, Indonesia, Japan, Taiwan (Liang et al, 2005), Thailand, Philipine, Malaysia (Page and Robins, 2006) and

Viet Nam (Levin et al, 2008)

Vermiculated sailfin catfish Pterygoplichthys disjunctivusis a kind of

ornamental fish imported to Viet Nam from Hong kong and Singapore Today, they appear with high density in natural reserves such as Tram Chim, U Minh Thuong, Lang Sen, Lung Ngoc Hoang and rivers, channels, canals, lakes,… in Mekong Delta

Pterygoplichthys disjunctivuscan be different others of Loricariids due

to their large dorsal fins with nine or more (usually 10) dorsal fin rays, which gives them their common name "sailfin catfish” Their dorsal and lateral surfaces covered with rough, bony plates forming flexible armor; the abdomen

is almost completely covered in small plates, the head is terete and naked Other characteristics of members of this genus include an inferior sucker mouth with thick, fleshy lips form a sucking disc for attaching to rocks and grazing on algae, they have adipose fin present, and an enlarged stomach connected to the dorsal abdominal wall by a connective tissue sheet The color

is generally dark brown or black

4 Nutritional characteristics

The stomach of Pterygoplichthys disjunctivus is greatly expanded with

the posterior portion forming a long, thin sac that is highly vascularized Their

mouth can cling to substrate even fast current of water, Pterygoplichthys disjunctivus feed primarily on benthic algae and detritus They may also eat

worms, insect larvae, fish eggs and other bottom-dwellers but the vast majority of its diet consists of detritus, algae, and various plant mater

5 Growth characteristics

The adult size of a member of Pterygoplichthys disjunctivus can range

from about 50–70 cm the female can spawn year round, survival rate of larvae

is 70%, they can live without food up to 1 month Their life is about 15 years (some situation is 30 years)

Pterygoplichthys disjunctivus can be found in a wide variety of habitats,

ranging from relatively cool, fast-flowing and oxygen-rich highland streams to slow-flowing, warm lowland rivers and stagnant pools poor in oxygen They

are tropical fish and populations are typically limited only by their lower lethal temperature which has been found to be about 8.8-11oC in some species They can thrive in a range of acidic to alkaline waters in a range of about (pH 5.5 to 8.0) They are often found in soft waters, but can adapt very quickly to hard

waters Pterygoplichthys disjunctivus is also highly tolerant to poor water

quality and is commonly found in polluted waters They are known to use outflow from sewage treatment plants as thermal refugia and can readily adapt

to changing water quality (Nico& Martin, 2001).Pterygoplichthys disjunctivus

may be found in from lowlands to elevations of up to 3,000m Kusunki, 2007) Some species are salt tolerant

(Wakida-6.Reproduction characteristics

Pterygoplichthys disjunctivus reproduces sexually and has high

fecundity The males construct burrows in the banks of the rivers and lakes in which they live Burrow width approximates that of the occupant fish (i.e., width between extended pectoral fins), burrow length is typically 0.5 to 1.0 m, and shape is variable although the tunnel usually extends downward into the bank These burrows are used for reproduction but also allow survival during drought Eggs are laid in the burrow and are guarded by males; fish can survive in the moist microhabitat even when water levels fall far below the opening to the chambers (Burgess 1989) Burrows may also be used as refugia during cold weather (Nico and Martin 2001) These traits enable sailfin catfish

to thrive in their natural and in unnatural habitats Dense populations of sailfin catfishes (hundreds to thousands per water body) have been observed in natural parts of their range (Burgess 1989) and in Hawaii, Puerto Rico, and

Florida (Nico 1999; Bunkley-Williams et al 1994) Growth is rapid during the

first two years of life (more than 35 cm) and fecundity is high (472-1283 mature eggs/ female) especially in larger individuals Consequently, introduced populations can become abundant in a very short period of time

Growth of Pterygoplichthys disjunctivus is rapid during the first two

years of life, with total lengths of many sailfin catfish exceeding 300 mm by

age 2 Specimens in aquaria may live more than 10 years The size range for most of the adult species in the Loricariid family is 30-50 cm, but individuals have been observed to reach 70 cm they start reproducing at approximately 25

cm

7 Environmental impacts

Potential effects of vermiculated sailfin catfish include

Impacts to native species: they are at a competitive disadvantage when confronted by larger (greater than 15 cm), longer-lived, highly productive, environ mentally tolerant species that feed on the same foods that they do Because they are bottom feeders, may vermiculated sailfin catfish incidentally ingest eggs of native fishes Because they are benthic and large, they may displace smaller or less aggressive benthic fishes

Alteration of bank structure and erosion: The nesting burrows of vermiculated sailfin catfish sometimes form a large group or “spawning colony” in which several dozen occur in very close proximity to each other (Nikolsky 1963) These colonies can compromise shoreline stability, increasing erosion and suspended sediment loads (Nico 2000a) Siltation, bank failure, head cutting, and elevated turbidity are likely impacts

Disruption of aquatic food chains: grazing on benthic algae and detritus

by vermiculated sailfin catfish alters and reduces food and physical cover Feeding on mud and silt could result in resuspension of sediments and/or changes in substrate size In addition, nutrients are prematurely diverted from the “consumer” components of food webs and transformed into feces available only to scatophagy and decomposers ( bacteria, fungi)

Mortality of endangered shore birds: because they are large, sedentary, and palatable, is attractive prey to fish-eating birds Their defensive erection of dorsal and pectoral spines endanger to the birds attempting to swallow whole fish

Changes in aquatic plant communities: they plough the bottoms of streams, occasionally burying their heads in the substrate and lashing their tails These behaviors can uproot or shear aquatic plants This would affect native plant species by reducing their abundance in beds of submersed aquatic

vegetation and creating mats that could shade them from sunlight

CHAPTER III MATERIALS AND METHODOLOGY

Duration: from July to October 2013

Location:

- Can Tho river, Ninh Kieu dictrict, Can Tho

- Truong Xuan commune, Thap Muoi dictrict, Dong Thap province

Figure 2: Sampling area in Can Tho

Figure 3: Sampling area in Dong Thap

Sampling area

Sampling area

1 Materials

Equipment: Bistoury, electronic scales, ruler, petri dishes, magnifying glass, other instruments

Chemical: Formalin, ethanol, HgCl2, nitric acid, pure water, glacial acetic

acid, Gilson ‘s fluid (separate eggs) Ingredients of Gilson ‘s fluid included

100ml ethanol 60o, 15 ml nitric acid 80%, 18 ml glacial acetic acid, 20g

mercuric chloride, 880 ml pure water

2 Methodology

2.1 Sampling and fixing samples

- The samples were collected from 30 to 40 individuals per month with 10-45 cm in length

- The fish were sampled by fishing equipments (trawl, seine, drift net) in rivers, canals, lakes or local market in Dong Thap and Can Tho provinces

- Samples were washed with freshwater and recorded time and places of sampling

- The samples were kept fresh for morphological and biological reproductive characteristics analysis in College of Aquaculture and Fisheries –

Can Tho University

2.2 Criteria for sample analysis

− Number of ripe eggs in sub-sample

− Weight of the ovaries

2.3 Length-weight relationship and condition factor (CF)

Length - weight relationship: The growth of fish could effect to its

length The cubic equation W = a.Lb was used for expressing the length – weight relationship In this equation, L and W were length and weight of fish, respectively, b was close to 3 in isometric growth and a is constant (King,

1995)

The individual variations from general length – weight relationship had been studied under the general name “condition.” The conditions of fish were influenced by the seasonal changes of gonads and by the feeding intensity King (1995) suggested the equation for calculate condition factor (CF) as follow:

Where:

CF: condition factor

W: weight of fish (g)

L: length of fish (cm)

b: the exponent of length – weight relationship equation in cubic form

2.4 Maturity stages, maturity proportion and sex ratio

In this research, it was required to examine the sex of a large number of samples According to information in table 3Maturity stages (Nikolsky 1963) ,sexual characteristics, maturity stages, reproductive ability of fishwere identified macroscopically by observating their gonads and using a magnifying glass Sex ratio depended on characteristics of species, reproduction, habitat,…

Table 1: Description of Maturity stages (Nikolsky 1963)

I Young individual is not sexually mature

II Gonads are small, eggs are invisible to naked eye

III Mature stage, eggs are visible to naked eye, testis is from pure white

to light pink, the weight of gonad increase quickly

IV Ripe stage, the gonad has biggest size, no fluid from gonad when

pressing

V Spawning eggs stage, having fluid from gonad when pressing, the

weight of gonad decrease quickly

VI After spawning stage, fluid from gonad is released completely, gonad

hole is swollen, and the gonad is very soft The female has a few eggs are remained; the male has a little sperm

2.5 Gonadosomatic Index (GSI)

Gonadosomatic Index (GSI) was one of several methods used for

determination the spawning season GSI of females and males were

significantly different, females had higher GSI than males because females had very heavier gonad than males in maturity stage The equation for

calculation the Gonadosomatic Index as :

Where :

GW: Gonad weight (g)

BW: body weight (g)

2.6 Hepatosomatic Index (HSI)

Hepatosomatic Index (HSI) was defined as the ratio of liver weight to body weight It provided an indication on status of energy reserve in an animal In a poor environment, fish usually have a smaller liver (with less energy reserved in the liver) HSI had been reported to decrease in fish exposed to high concentrations of cadmium and zinc HSI might be useful as anindicator of chemical water pollution, others showed that it was inconsistent

as a biomarker and that it was depend on the seasonal cycle

F=

Where:

F : fecundity (eggs/female or eggs/gram of female)

n : number of ripe eggs in sub-sample

G : weight of the ovaries (g)

g : weight of the sub-sample (g)

Relative fecundity : used to compare fecundity between individuals or populations in the same species that were different about age, size, habitat…it was indicated by fecundity devided to weight of fish Relative fecundity was very important because we could calculate amount of eggs in a unit of weight

2.8Total length at first maturity (Lm)

Total length at first maturity of fish (the total length at which 50% of the fish became mature) was determined from the relationship between the percentages of mature fish and the total length classes The proportion (P) of sexually mature of total length was fitted to equation which was in S line form:

2.9Data analysis method

The data was checked and typed into computer After that, data was calculated in Microsoft Excel and written in Microsoft Word for report

CHAPTER IV RESULTS AND DISCUSSIONS

Amount of samples: 126

Length:8.3-45 cm

Location:

- Can tho river, Ninh Kieu dictrict, Can Tho

- Truong Xuan commune, Thap Muoi dictrict, Dong Thap province

1 Morphological criteria and characteristics

Table 2: Comparison of morphological criteria between Pterygoplichthyus

disjunctivus (Weber, 1991) with other researchs

Criteria This research Fishbase (2011) Chavez (2006)

From this table, results were collected about morphological criteria of

Pterygoplichthyus disjunctivus were suitable with other researches

Table 3:Propotion of morphological criteria ofPterygoplichthyus

disjunctivus

Criteria Min (cm) Max (cm) Mean (cm)

Length of head/ distance of eyes 0.82 2.24 1.43

Distance of eyes/ standard length 0.08 0.22 0.14

Figure 4: Vermiculated sailfin catfish (Pterygoplichthyus disjunctivus

Weber, 1991)

Figure 5: sucker mouth of Vermiculated sailfin catfish (Pterygoplichthyus

disjunctivusWeber, 1991)

Pterygoplichthyus disjunctivus(Weber, 1991) was black or dark brown,

body and fins had the same color, body and head did not have scales, it had a big head, terete suckermouth with fleshy lips form a sucking disc which was near abdomen, black irises in eyes, dorsal fin was big and long which would

be bristled if it panic, hard and rough back because of bony plates formed flexible armor, abdomen was covered completely by patterned, small and thin

plate

2 Length – weight relationship and condition factor (CF)

2.1 Total length – weight relationship

Total length – weight relationship was determined from 126 samples of

Pterygoplichthyus disjunctivus in 4 months, average total length was 25.2cm

(8.3 – 45cm) and average of weight was 130.4g (6.13 – 660g) The relationship was showed by equation W = 0.0115L2.8967 with R2 = 0.9759 The result indicated close relationship between total length and weight

2.2 Standard length – weight relationship

Standard length – weight relationship was determined from 126

samples of Pterygoplichthyus disjunctivus in 4 months, average standard

length was 16.7cm (5.6 – 33.5cm) and average of weight was 130.4g ( 6.13 – 660g) The relationship was showed by equation W = 0.0759L2.5647 with R2 = 0.9485 The result indicated close relationship between standard length and weight

According to these figures, growth of Pterygoplichthyus

disjunctivuswas not stable, growth depended on every maturity stage and age

of fish When the fish were young, they grew mostly in length and when they

were elder, they grew mostly in weight The fish grew quickly before maturity

and they had gradually slow growth after maturity, finally is stopping growth

in reproductive time

Compare total length–weight relationship between this research (W= 0.0115L2.8967, n=126) with Huynh Thi Hoang Oanh (2012) ( W= 0.0116

L2.882, n=680 ) and compare standard length–weight relationship between this

research (W = 0.0759L2.5647,n=126) with Nguyen Hong Tan Phat (2011) (W =

0.042 L2.6813, n=120 ), they were different because of different amount of

samples, sample sizes, habitat of fish and experimental manipulation

2.3 Condition factor (CF)

Table 4: Condition factor (CF) of Pterygoplichthyus disjunctivus(males)

Month Amount of samples Mean of CF Standard deviation

0.0115 0.0114

Figure 8: Condition factor (CF) of Pterygoplichthyus disjunctivus(males)

According to table 6 and figure 8, condition factor of males was quietly stable, the highest CF was in September (0.0119) and the lowest CF was in October (0.0111), so September was suitable month for reproduction

of males because the fish had convenient habitat and stimulated enough energy for maturity and reproduction

Table 5: Condition factor (CF) of Pterygoplichthyus disjunctivus(females)

Month Amount of samples Mean of CF Standard

0.0119 0.0116

0.0112 0.0117

Figure 9: Condition factor (CF) of Pterygoplichthyus disjunctivus(females)

According to table 7 and figure 9, CF of females was also quietly stable, the highest CF was in October (0.0119) and the lowest CF was in August (0.0112), so October was suitable for reproduction of females

Compare to Nguyen Hong Tan Phat (2011), CF of Pterygoplichthyus disjunctivus was the highest in September (0.0470) and the lowest was in

November (0.0400) Different results between researches were from differences of sampling time and location, sizes of samples, habitat of fish

or seasons

3 Maturity stages, maturity proportion and sex ratio

3.1 Maturity proportion and maturity stages

Table 6: Maturity proportion (%) of Pterygoplichthyus disjunctivus

Month

Amount of samples

Immaturity (%)

Maturity (%)