tóm tắt luận án study on the biological characteristics and induced spawning of spotted scat

Experiment setting 2.2.1 The sudy on reproductive biology characteristics Thirty spotted cats was collected monthly during 12 months to record the individual weight, sex ratio, the weigh

MINISTRY OF EDUCATION AND TRAINING

CAN THO UNIVERSITY

LY VAN KHANH

STUDY ON THE BIOLOGICAL CHARACTERISTICS AND INDUCED SPAWNING OF SPOTTED SCAT

(Scatophagus argus Linnaeus, 1766)

Specialization: Marine/Brackishwater Aquaculture

Field of Study Code: 62 62 70 05

Dissertation of Doctor Degree in Aquaculture

Can Tho, 2012

The study carried-out at:

- Ngoc Hien and Nam Can district, Ca Mau province.

- College of Aquaculture and Fisheries, Can Tho

University.

Supervisors:

A/Prof Dr Nguyen Thanh Phuong

A/Prof Dr Tran Thi Thanh Hien

Examiner 1: A/Prof Dr Nguyen Tuong Anh

Examiner 2: Dr Bui Minh Tam

The dissertation will be defensed at the university committee in meeting room of College of Aquaculture and Fisheries, Can Tho University at time of: ….… hr ….… date …… month

…… year 2012.

The disseratation is available in Libraries:

 Library Center of Can Tho University.

 College of Aquaculture, Can Tho University.

Introduction

1 Background and problem statement

Viet Nam has a great potential for marine/brackish-water

aquaculture of Viet Nam is likely based on single species and its negative impacts on water environment and disease outbreak have occurred The diversification of farming species in the coastal areas is very important for sustainable development; and few brackish-water fish species has been introduced to farm at pilot scale However, the development of marine/brackish-water species has faced various difficulties, especially hatchery-reared seed supply, which is considered a basis requirement

Spotted cat (Scatophagus argus) distributing along the coastal

areas is the potential species for aquaculture especially in the Mekong delta However, there are short of seeds in both of wild and hatchery seeds for culture systems Therefore, the biological characteristics and

induced spawning of spotted scat fish (Scatophagus argus Linnaeus,

1766) is needed to be studied for developing aquaculture production

of this species

2 The Objective of Study

- General objective: to find out the biology characteristics to

contribute the scientific information or development of artificial propagation of spotted cat; to diversify the aquaculture species and farming systems in the coastal areas; to archive the sustaining development of aquaculture in the Mekong Dleta and Vietnam

- Specific objective: to determine the main biology including

physiological characteristics, kinds of ganodotropic hormones/and chemicals corresponding with artificial propagation in Spotted cat hatchery; to develop the techniques in nursing Spotted scat from fry to fingerling stage

3 The Contents of Study

- The study on the main biology and physical characteristics relating to the reproduction of Spotted cat

- The study on the investigation/and use of ganodotropic hormones and chemicals in the artificial propagation reproduction and hatching techniques of Spotted cat

- The study on the development of digestive system (intestine) and feeding habits of fry of Spotted cat

- The study on nursing Spotted cat from fry stage to small fingerling with different feeds; and nursing small fingerling to fingerling at different salinities

4 The useful outcomes

The findings of the research provide basic scientific information of reproductive and physiological biology of spotted cat; and induced spawning and larvae to fry and fry to fingerling rearing The above information will be utilized for the complete development of seed production techniques of the spotted cat, which is important for spotted cat grow-out activities, contribution to diversification of farming species and sustainable development of marine/brackish-water aquaculture in Viet Nam especially in the Mekong Delta

5 New findings of the thesis

- Spawning seasons, relative fecundity, egg diameter and embryo development of spotted cat were determined

- Relationship between hematological parameters (red blood cell, white blood cell, hematocrit, ), phosphate protein (vitellogenin) concentration and maturation stages of spotted cat were established

- Yolk sac size (length and width), larval month size, larval length, yolk sac absorption duration, and larval initial food selection and digestive tract development were found

- More especially, technique for induced spawning was successfully found; initial food for newly hatched larvae up to 30 days was identified; and the suitable salinity for nursery of fish from 30 to

60 days was also chosen

The above results indicated that the technique of artificial propagation and larval rearing of spotted cat were established and is able to produce mass seeds for grow-out activities, diversification of farming species, and farming models as well The thesis also indicates

possibility to close the life cycle of the spotted cat in captive conditions

6 The lay-out of dissertation

The dissertation has 163 pages It consists of 5 pages of introduction, literature review 30 pages, methodology 20 pages, results 57 pages, conclusion and recommendation 3 pages, list publication 2 pages, cited references 15 pages and 31 pages of indices

Chapter 1: Literature review

The literature review focused to investigation of main points following as:

- The biology characyeristics of Spotted cat

- The physiological characteristics of Spotted cat

- The ganadotropic hormones and chemicals corresponding with spotted cat

- The imformation relating to the techniques in hatchery of marine/brackish water fishes

- Development of intestine system and feeding habits of spotted cat

- Natural food and compound feeds used for rearing fry of fish

- The issues studied on natural food/ compound feeds and salinity

in the nursing marine fishes

In the results of the previous studies, the biological characteristics

of spotted cat are not studied completely; the hatchery seed production

is not successful However, based on the information reviewed the new studies are established to determine the biology characteristics of Spotted cat and find the techniques of hatchery seed reproduction

Chapter 2: METHODOLOGY 2.1 Location and time of the study

The study was carried-out at Nam Can and Ngoc Hien districts, Ca Mau province; and the hatchery of College of Aquaculture and Fisheries, Can Tho University, from September 2006 to November 2010

2.2 Experiment setting

2.2.1 The sudy on reproductive biology characteristics

Thirty spotted cats was collected monthly during 12 months to record the individual weight, sex ratio, the weight of gonad, maturation indexes, female and male ratios, phases of development of gonad and diameter of eggs

The relationship among the development of gonads, maturation rate of fish and fat indexes of Fulton and Clark were investigated based on the fish samples collected The weight of fish, standard length, weight of fish without viscera, fat indexes of Fulton and Clark, sex ratios, weight of gonad and the development phases of gonad are monitored

Mature broodstocks catched from wild were stimulated for spawning by using gonadotropic hormones and chemicals for recording the spawning capacity, diameter of eggs, development of embryos, size of egg yolk, size of mouths, length of fries

2.2.2 The study on physiological characteristics of spotted cat

The collected samples of spotted cat were recorded as six phases

of gonad development, weight of fishes, sex ratios, weight of gonads and maturation ratios

The blood samples of fishes were collected from the dorsalis by using syringe The blood characteristics analalysed following asnumber of red blood cells, leukocyte, haemoglobin, ratio of

of haemoglobin in red blood cell (MHC), concentration of haemoglobin in red blood cell (MHCH), concentration of protein, phosphate in the plasma (Vitellogenin), concentration of protein in muscle and liver

2.2.3 The experiments of spawning stimulation and hatching eggs of spotted cat

2.2.3.1 Study on the maturation culture of spotted cat

One-year-old broostocks from hatchery reared fish were grew-out

The fish was fed 2 twice a day by using 35% protein commercial feeds (Grobest Company) In the experiment, the parameters of water quality were determined such as total amonia nitrogen (TAN), nitrite

gonad, indexes and matuarion of ratios

2.2.3.2 Study on the kinds and doses uses of gonadotropic hormones and chemicals corresponding with artificial reproduction

The mature broodstocks collected from the wild were stimulated for artificial reproduction (Table 2.1) The female broodstocks were injected by 2 times (preparatory and decisive injections), meanwhile the male is injected 1 time at the same time as the decisive injection of female

After decisive injection, the activities of the broodstocks were monitored; when the females were ovulating, testises of males were dissected and ground to get the sperms for fertilizing the eggs latter.The eggs and sperms were mixed well and hatched in 30‰ salinitywater

Table 2.1: Kinds and doses of gonadotropic hormones and chemicals use

Fig 2.2: The procedure deneating the artificial reproduction of Spotted cat

2.2.3.3 The effects of salinities on hatching rates

The wild mature spotted cat injected ovaprime with dose of 1mL/kg (see types and doses used in section 2.2.3.2) The eggs and sperms were mixed well and incubated in 7 treatments with 0, 5, 10,

15, 20, 25 and 30‰ of salinities using 15-liter tanks aerated The incubating density was 100 eggs per liter The temperature, pH and hatching rates were recorded

2.2.4 Study on the development of digestion system and feeding habit of fry

with salinity of 25‰; density of 50 fries per liter and aerated condition The fries were fed natural foods with twice a day The natural foods were collected from water of extensive shrimp ponds using phytophankton scope net

2.2.4.1 Study on the development of digestion system of spotted cat

From the tanks mentioned above, the fry samples were collected at

2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25 and 30-day-old to analyse histology for determining devlopment of enteron system

2.2.4.2 Study on the food selection and consumption of spotted cat

The water sample of the tanks metioned above, were taken at 2, 3,

4, 5, 6, 7, 8, 9, 10, 15, 20, 25 and 30-day-old of fry to determine the quantity and quality of phytoplankton and zooplankton Based on the frequency of occurrence of each species of planktons in the samples toclarify the food section and the consumption of spotted cat

2.2.5 Nursing fry to small fingerling (1-month-old)

2.2.5.1 The nursing fry to 15-day-old fingerling using different feeds

The 2-day-old fries were reared in 15-liter tanks at the salinity of25‰; 50 fries per liter density with 6 treatments of different types of

feeds including (i) Chlorella sp.+Rotifer; (ii) Chlorella sp.+Rotifer+ Compound feed (TACB); (iii) Chlorella sp+TACB; (iv) Rotifer; (v) Rotifer+TACB; and (vi) TACB.

During 15 days of rearing, the fries were fed 4 times daily The water temperature and pH, length, the growth/and specific growth of fish length, and the survival rates of fries were determined

2.2.5.2 The nursing 15 to 30-day-old fingerling using different feeds

The 15-day-old fingerlings were grew-out in the 10-liter tanks with 25‰ salinity The experiment has 5 treatments with feeding by

different feed stuffs including (i) Rotifer; (ii) Artemia; (iii) Compound feed (TACB); (iv) Rotifer+TACB and (v) Artemia+TACB

The fingerlings were fed 4 times per day during 15 days (15-30 day-old)

The water quality and the growth of fish were verified by temperature, length, the growth /and specific growth of fish length, and the survival rates

2.2.6 Nursing the fingerling 30 to 60-day-old at different salinities

The experiment has seven treatments including 0, 5, 10, 15, 20, 25 and 30‰ salinity Twenty-five fingerlings were nursed in the 50-liter tanks and fed by commercial feeds at the frequency of 3 times per dayDuring 30 days nursing, the water temperature and pH, weight, the growth /and specific growth of fish, survival rates and size distribution

of fish were recorded

The collected data were analysed in the differences of means among the treatments using the one-way ANOVA with DUNCAN test(using Excel 2003 and SPSS version 13.00)

Chapter 3: RESULTS AND DISCUSSION

3.1 The reproductive biology characteristics of spotted cat

3.1.1 The stages of gonad development

The developmental stages of reproduction system were identified based on the histology specimens and the maturity scale of Nikolsky (1963)

3.1.1.1 The development stages of testicle

Fig 3.1: The histology of testicle Fig 3.2: The morphology of testicle

3.1.1.2 The development stages of ovary

Giai đoạn I (40x) Giai đoạn II (40x)

Giai đoạn III (20x) Giai đoạn IV (10x)

Stage I (40X) Stage II (40X)

Stage III (20X) Stage IV (10X)

Fig 3.3: The histology of ovary

Giai đoạn I Giai đoạn II

Giai đoạn III Giai đoạn IV Stage I Stage II

Stage IV Stage III

Fig 3.4: The morphology of ovary

3.1.2 The spawning season and sex ratio of Spotted cat population

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

Tháng

Đực Cái

month

male female

Fig 3.7: The ratio of female and male

3.1.3 The relation of development stage of gonad with maturation and fat index of female spotted cat

The gonadosomatic index of spotted cat with stage IV was 9.87%, the highest compared to other stages The spotted cat with stage III

ovary had highest fat index (Table 3.1); the ratio of maturation increased from stage III to stage IV ovary, meanwhile the fat index decreased from stage III to stage IV ovary

Tbale 3.1: Maturation ratio and fat indexes of gonad development stages of female

spotted cat

Development

stage of gonad

Gonadosomatic index (GSI) (%)

Fat index of Fulton (%)

Fat index of Clark

Table 3.2: Maturation ratio and fat indexes of gonad development stages of male

spotted cat

Development

stage of gonad

Gonadosomatic index (GSI) (%)

Fat index of Fulton

3.1.5 Spawning capacity of spotted cat

The spawning fecundity of spotted cat was 2.469.209 eggs/kg (Table 3.3)

Table 3.3: The spawning capacity of spotted cat

Weigh of fish (g/fish) Spawning capacity (eggs/kg of fish)

Table 3.4: Diameter of Spotted cat egg

Diameter (mm) Stage III Stage IV Stage V Before absorbed

water

After absorbed water Mean 0.37±0.02 0.58±0.03 0.68±0.02 0.71±0.02 0.80±0.02

3.1.6.2 The developmet of embryo

The time of embryo developing ranges from 18 to 22 hours (mean

(Table 3.5)

Table 3.5: Development of embryo of Spotted cat

Development stage After egg fertilized Temperature ( o C) pH

The newly hatched fries use yolk egg for developing in 2 days, after that the fry colects the food from waterbodies (Fig 3.8)

64 cells Gastula Neutron embryo Complete embryo

Fig 3.8: Development stage of embryo of Spotted cat (10X)

3.1.6.3 The size of egg yolk, the size of mouth and the length of spotted cat fry

The fry of spotted cat has the egg yolk with 0.76 mm (length) and0.29 mm (width); the size of mouth 0.07 mm and total length 1.88

mm The egg yolk was consumed until day 3-4, at that time the fry had to feeding the food by the mouth with size 0.23±0.04 mm width (Table 3.6 and Fig 3.9)

Table 3.6: The sizes of egg yolk and mouth of spotted cat

Size of egg yolk (mm)

Age

Size of mouth (mm)

Total length (mm)

0 5 10 15 20 25

1 2 3 4 5 Development stage of gonad

Gonad Liver

Figure 3.11: Relation between weight of gonad and weight of liver based on different stages of gonad development

5 10 15 20 25 Length or height (cm)

Tolal length (Lt) Standard length (Lc) Height

Figure 3.10: The relation beween weight and the total length/height of female Spotted cat

Fig 3.9: Spotted cat fry 1 to 30-day-old (4X)

3.2.1 The reproductive physiology cheracteristics of female Spotted cat

3.2.1.1 Relation between weight and length/height of female Spotted cat

Fig 3.10 indicated that the

exponiential coefficient of total

length (2.75), standard length

(2.78) and height (2.99) is

smaller than 3

The weight of fish had

strongly relation with total

length, standard length and height of fish

3.2.1.2 The relations between GSI and ratio of liver weight per fish weight (HIS); and ratio

of gonad weight per liver

weight of female Spotted

cat

The weight of livers of female

having ovaries in stage III and IV

were heavier than that of fish

with ovaries in stage I and II

to that of other group of fishes (Table 3.7)

The weight of liver of fish increased by the increasing of vorary from stage I to II and decreased at stage IV of ovary (Table 3.7 and Fig 3.11)

Table 3.7: Ratio of liver weight per fish weight, ratio of gonad weight per liver

weight of fishes having different stages of gonads

Gonad stage GSI (%) Weight of

liver (g)

Weight of liver/weight of fish (HSI) (%)

Weight of gonad /weight of liver (%)

Table 3.8: Phisical blood characteristic of female Spotted cat based on different

stages of gonad development

IV 6.83 a ±1.20 31.0 a ±7.54 21.3 a ±10.0 22.0 a ±3.50

The means with different superscripts within the same column indicate significant differences among stages of gonad development (P<0.05)

3.2.1.4 The relationship between development stages of gonad to quantity of red blood cell, leukocyte and ratio of leukocyte/red blood cell of female Spotted cat

The quantity of red blood cell, volume of red blood cell belonging

to different developments stage of gonad in the fishes expressed no significant differemces (p>0.05) (Table 3.9)

Table 3.9: Quantity of red blood cell and leukocyte, volume of red blood cell and

ratio of leukocyte/red blood cellin different stages of gonad development

Quantity of leukocyte (million cell /mm 3 )

Ratio of leukocyte/red blood cell (%)

I 4.19 a ±1.32 84.9 a ±37.4 0.0 5 b ±0.02 1.12 b ±0.51

II 3.45 a ±1.28 104 a ±49.5 0.03 ab ±0.01 0.93 ab ±0.54 III 3.13 a ±0.91 93.8 a ±12.9 0.02 a ±0.01 0.67 a ±0.10

3.2.1.5 The relationship between development stages of gonad to

phosphate protein content of blood plasma and protein of female broodstocks

The phosphate protein content in fish blood and muscle between differrent stages of gonad development is not significant difference statistically (p>0.05) (Table 3.10) Protein content in the liver of female broodstocs at the gonad stage I was the biggest (12.3mg protein/mL blood plasma), and there is no significant difference to that of the gonad stage II and III (p<0.05)

Table 3.10: The relationship between development stages of gonad to phosphate protein content of blood plasma and protein of female broodstocks

Protein muscle (mg protein/mL blood plasma)

Protein liver (mg protein/mL blood plasma)

I 1.26 a ±1.04 41.5 a ±13.1 6.42 a ±4.01 12.3 b ± 3.44

II 1.87 ab 1.85 43.0 a ±11.7 8.41 a ± 7.34 10.1 a ±1.34 III 2.68 bc ±1.43 43.5 a ±8.78 7.54 a ±2.77 9.74 a ± 2.49

3.2.2 The reproductive physiology cheracteristics of male Spotted cat

3.2.2.1 Correlation between

weight and length, heigth

Correlation between weight

and length, heigth of male

broodstocks was the same as

female broodstocks’s trend (Fig

3.12)

3.2.2.2 The relationship between stage of gonad development to

weight of liver/weight of fish and weight of gonad/weight of liver of male spotted cat

Based on the different stages of gonad development of the male spotted cat, the significant differences of the ratio of weight of liver/weight of fish, and ratio of weight of gonad/weight of liver were not found (p>0.05)

Figure 3.12: Relation between weight

of fish and length/height of fish