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

CAN THO UNIVERSITY COLLEGE OF AQUACULTURE AND FISHERIES NATURAL FOOD COMPOSITION IN THE POND AND DIGESTIVE TRACT OF STRIPED CATFISH Pangasianodon hypophthalmus DURING NURSERY STAGE By

CAN THO UNIVERSITY COLLEGE OF AQUACULTURE AND FISHERIES

NATURAL FOOD COMPOSITION IN THE POND AND DIGESTIVE TRACT OF STRIPED CATFISH

(Pangasianodon hypophthalmus) DURING NURSERY

STAGE

By NGUYEN LAM PHUONG NGOC

A thesis submitted in partial fulfillment of the requirements for

the degree of Bachelor of Aquaculture

Can Tho, December 2013

CAN THO UNIVERSITY COLLEGE OF AQUACULTURE AND FISHERIES

NATURAL FOOD COMPOSITION IN THE POND AND IN THE DIGESTIVE TRACT OF STRIPED

CATFISH (Pangasianodon hypophthalmus) DURING

NURSERY STAGE

By NGUYEN LAM PHUONG NGOC

A thesis submitted in partial fulfillment of the requirements for

the degree of Bachelor of Aquaculture Science

Supervisor Assoc Prof Dr VU NGOC UT

Can Tho, December 2013

APPROVEMENT

The thesis “Natural food composition in the pond and digestive tract of

Striped Catfish (Pangasianodon hypophthalmus) during nursery stage”

defended by Nguyen Lam Phuong Ngoc, which was edited and passed by

committee on December 27 th, 2013

Assoc Prof Dr Vu Ngoc Ut Nguyen Lam Phuong Ngoc

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ACKNOWLEDGEMENT

First of all, I want to express my special thanks to my supervisor, Associate Professor Dr Vu Ngoc Ut for being invaluable guidance, advice, and encouragement to my thesis completion

Many thanks are also given to all other teachers of the College of Aquaculture and Fisheries, and especially to those of the Department of Applied Hydrobiology for providing me with great working and learning conditions

I would love to express my sincere appreciation to miss Nguyen Hong Linh, master student of Aquaculture Course 19 for her unconditionally kind help throughout the experimental period

Last but not least, I really want to thank my academic adviser, Dr Duong Thuy Yen, who was guiding and encouraging me over the last four years, and

my family, my friends in Advance Aquaculture Class Course 35 for their great lifetime support which makes everything possible for me

Nguyen Lam Phuong Ngoc

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ABSTRACT

Study on natural food composition in the pond and in the digestive tract

of Stripped Catfish (Pangasianodon hypophthalmus) during nursery stage

served as base for improving and enhancing survival rate of fry stage The study was carried out in Tien Thuy – Chau Thanh Hatchery of Ben Tre Seafood Import – Export Joint Stock Company during 28 nursery days; fifteen days collected sample in three nursery ponds The samples were collected a day before stocking fish, everyday in the first week and three day intervals The result obtained in nursery ponds showed that there were 140 species of zooplankton including 36 species of Protozoa, 56 species of Rotifera, 17 species of Cladocera, 30 species of Copepoda and Nauplii In the water supply canal, 16 species of zooplankton were recorded includeding 5 species of Protozoa, 6 species of Rotifera, 3 species of Cladocera, 2 species of Copepoda and Nauplii The density of zooplankton in the pond varied from 5,889 to 4,680,000 inds/m3 and in the water supply canal varied from 2,778 to 250,000 inds/m3 In the digestive tract of the fry, 4 zooplankton groups were found Rotifera accounted for 5.16%, Protozoa 0.15%, Cladocera 68.29%, Copepoda 24.15% and Nauplii 0.83% Result from natural food in the digestive tract indicated that Cladocera was the most favorite food of Stripped Catfish in first seven days after stocking and during nursery stage These results showed the abundant food selection of Stripped Catfish fry in nursery pond with many different natural food compositions

Keywords: Zooplankton, nursery stage, digestive tract

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TABLE OF CONTENTS

ACKNOWLEDGEMENT i

ABSTRACT ii

TABLE OF CONTENTS iii

LIST OF FIGURES v

LIST OF TABLES vi

LIST OF ABBREVIATIONS vii

CHAPTER 1 INTRODUCTION 1

1.1 Background of study 1

1.2 Research objectives 2

1.3 Research contents 2

CHAPTER 2 LITERATURE REVIEW 3

2.1 Situation of Striped Catfish seed production in the Mekong delta 3

2.2 Biological characteristics of Striped Catfish 4

2.2.1 Classification 4

2.2.2 Distribution 4

2.2.3 Morphological characteristics 5

2.2.4 Nutritional characteristics 5

2.2.5 Growth characteristics 6

2.2.6 Reproductive characteristics 6

2.3 The role of natural food in aquaculture 7

2.3.1 Rotifer 8

2.3.2 Copepoda 10

2.3.3 Cladocera 12

CHAPTER 3 METHODOLOGY 14

3.1 Location 14

3.2 Time 14

3.3 Equipments 14

3.4 Sampling method 14

3.4.1 Fish specimens 14

3.4.2 Zooplankton sampling 14

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3.4.2.1 Qualitative analysis 15

3.4.2.2 Quantitative analysis 15

3.5 Sample analysing method 15

3.5.1 Zooplankton analysis 15

3.5.1.1 Qualitative analysis 15

3.5.1.2 Quantitative analysis 15

3.5.2 Fish sampling analysis 16

3.6 The method for data analysis 18

CHAPTER 4 RESULTS AND DISCUSSION 19

4.1 Zooplankton species composition 19

4.1.1 Zooplankton composition in nursery ponds 19

4.1.2 Zooplankton composition the water supply canal 19

4.2 The density of zooplankton composition 20

4.2.1 The density of zooplankton composition in nursery ponds 20

4.2.2 The density of zooplankton composition in the water supply cannal 23

4.3 The zooplankton size in nursery pond 24

4.4 Mouth gap size of Striped Catfish in nursery stage 24

4.5 Natural food composition in the digestive tract in 28 nursery days 26

4.5.1 Frequency of food composition in digestive tract 26

4.5.2 Point counting of food composition in digestive tract 27

4.5.3 Combination point counting with frequency of food composition in digestive tract 25

4.5.4 Coefficiency of food choice of Striped Catfish in 28 nursery days 29

CHAPTER 5 CONCLUSIONS AND RECOMMENDATION 30

5.1 Conclusions 30

5.2 Recommendation 30

REFERENCES 31

APPENDICES 34

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LIST OF FIGURES

Figure 2.1 The external image of Striped Catfish

Figure 2.2 Some species of rotifer

Figure 2.3 Some species of copepod

Figure 2.4 Some species of cladocera

Figure 4.1 The percentage of zooplankton species groups in nursery pond Figure 4.2 The percentage of zooplankton species groups in the water supply canal

Figure 4.3 The density of zooplankton (inds/m3) in nursery pond

Figure 4.4 The density of zooplankton (inds/m3) in the water supply canal Figure 4.5 Mouth gap size of Stripped Catfish fry (µm) in 28 nursery days

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LIST OF TABLES

Table 4.1 Mouth gap size of Striped Catfish in 3 nursery ponds

Table 4.2 Frequency (%) and the rate (%) of food composition in digestive tract with age

Table 4.3 Analysing result of point counting of food composition in digestive tract in 28 nursery stage

Table 4.4 Analysing result of food composition in digestive tract by

combination point counting with frequency

Table 4.5 Coefficiency of food choice of fry in 28 nursery days

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CHAPTER 1 INTRODUCTION 1.1 Background of study

In recent years, aquaculture has been developed rapidly around the world Especially in Vietnam, the movement of culturing Striped Catfish has developed exceeding planning production Aquaculture provided 52% of production and more than 60% value of exports in which Striped Catfish reached high number of export turn over Mekong Delta has the advantages for culturing Striped Catfish Can Tho, An Giang, Dong Thap provinces provide large seed resources for aquaculture processing factory In 2012, the total production of Striped Catfish in the region reached nearly 4.6 billion (increased nearly 2 times compared with 2011) According to Directorate of Fisheries Statistics 2012, the region exported 53,000 tons of catfish, raised the total amount of fish exported to 592,000 tons, valued at $1.6 billion Compared with 2011, the area of cultured pond increased 11.6% (5,300ha) but the total value of exports fell by 2.2% due to Tra catfish price reduced from 0.2 to 0.4 USD / kg Besides, catfish industry must be facing with difficulties due to the shorten of materials Commercial fish farming reach high efficiency depends on many factors, the quality of fingerling is one of the decisive

factors

Fingerlings are the important factor to help improve the quality as well

as production of Striped Catfish, at the same time; it increases profits and minimizes risks for farmers However, the quality of seed is decreasing because famers have not cared about fingerling quality In fingerling production, food and feeding technique are very important in nursing fish Today, although there are many advanced techniques in the artificial food production for larvae, but live food such as algae, rotifers, crustaceans, artemia are still considered very important and have great potential in the seed production One of matters need special interest is shorten of natural food in nursery stage In fry stage, mouth size of larvae is small, the sensory organs as eyes, touch, lateral line organs have not developed fully and the digestive system is not complete; so limiting the selection and proper use of feed during starting eating outside (Vu Ngoc Ut, 2012) In nursery stage, natural food plays an important role in growth and survival rate Natural food is the most favorite food of fish in stage from fry to fingerling Natural food compositions

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affect to survival rate and fry quality in the pond Especially, natural food provides essential nutrient for larvae Although there have been much researches on the composition of fish food during nursery stage, they still are not complete This problem needs more investigable research in order to

ensure the survival and growth rate of fish The experiments on “Natural food

composition in the pond and digestive tract of Striped Catfish (Pangasianodon hypophthalmus) during nursery stage” will identify natural

food ingredients for nursery stage Besides, it provides some information

about the efficiency of natural food in aquaculture

1.2 Research objectives

To investigate the composition of natural food in the ponds and digestive tract of striped catfish during the nursery stage to serve as base for providing appropriate feeding regimes to improve survival rate of fish fingerlings

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CHAPTER 2 LITERATURE REVIEW 2.1 Status of Striped Catfish seed production in the Mekong Delta

Mekong Delta is one of seven important economic regions of Vietnam Nature area is approximate 4 million hectare, about 12% total area of the country (Directorate of Fisheries Statistics, 2009) From the first half of the 20th century, catfish farming in ponds began to practice in the Mekong River Delta and had contributed to provisions for people But in the dry season, the amount of fish in the river was decreasing due to the fry river; fish was pulled out of the sunken field so fish provided for market was scarce Due to before

1970 fishery was restricted culturing techniques and fingerlings, most Striped Catfish broodstock resources completely depended on nature From the 1980s, Mekong Delta had just begun to research and successed in Striped Catfish artificial breeding after more than 30 years of natural breeding dependence However, until 1990s, farmers had just used widely fingerlings Especially, from 1999 to now, fingerlings supplied all Striped cultured sources with an average output of 1.5 - 2 billion fish/ year From only a few households until now the whole area had 5,775 breeding households (Pham Van Khanh, 2006) Thence, fry nursery industry began to develop and concentrated mainly in the region as Tan Chau, Chau Doc, Hong Ngu, islands on Tien river as Long Khanh, Phu Thuan Early 1990s, fry yield catched anually reached only 150 –

200 million fries (Vuong Hoc Vinh, 1994) Nowaday, the demand of Tra fingerling is about 1.8 to 2.4 billion fries every year Mekong Delta has about

200 breeding hatcheries and 4000 households nursing fry on the density more than 2,500 ha with total productivity is more than 2 billion fingerlings, fry productivity in region meet livestock demand (Ministry of Agriculture and Rural Development, 2012) In particular, provinces produce many Striped Catfish fry are Dong Thap, Can Tho, and provinces have many nursing hatcheries are Can Tho, An Giang, Dong Thap and Tien Giang However, due

to the unstable fish material market that makes farmers feel less secure to invest in production Many households are not interested in seed quality, production and business conditions do not also ensure regulations Thereby it causes loss in the rearing; the loss ratio exceeds 30% of the number of fish stocked

Species Pangasianodon hypophthalmus

Figure 2.1 The external image of Striped Catfish

2.2.2 Distribution

Striped Catfish distribute in Mekong River Basin, present in all four countries Vietnam, Laos, Cambodia and Thailand In Vietnam, many years ago, when there was no artificial broodstock, fry and fingerling, they were usually captured on Hau and Tien River Mature fish only found in the ponds, rarely in the wild region of Vietnam, due to fish migrated up Mekong River to live and find out where natural reproduction

- Teeth small, smooth; palate teeth are divided into 4 small, slim patches

- Two barbels; extending maxillary barbel not beyond a vertical pectoral fin margin; mandibular barbel shorter

- Posterior naris closer anterior naris than eyes and in a straight line drawn from the nose to the edge of the eye holes

- Body elongate; lateral part flat; lateral line complete, branch, starting from gill margin to the middle of caudal fin

- The back of the spine of dorsal fin, pectoral fin serrate down the caudal fin

- Pelvic fin extending not touch posterior point of anal fin

- In large fish, the back of body and head blue gray or brown black and pale down abdomen, abdomen silver white

- Pelvic fin and anal fin yellow

2.2.4 Nutritional characteristics

After finishing the yolk sac, fry fish begin to use external food such as rotifer, waterflea The common food of fingerling is not larger than the diameter of the eyes, but for Striped Catfish, preys that they catch are much larger than the diameter of their eyes (Pham Van Khanh, 2006) Artemia lavae give high survival rate and best growth (Duong Thuy Yen, 2003)

Striped catfish is omnivorous but they have inclining to eat animals, food from animals will help fish grow faster In nature, fish eats organic humus, aquatic roots, vegetable, shrimp, crab, insects, snail and fish Fish in culture pond can use different food as trash fish, pellets, bran, groat, spinach, (Duong Nhut Long, 2004)

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2.2.5 Growth characteristics

Striped catfish grows very fast, small fish grows length fast, fish reaches 10 – 12 cm length, 14 – 15g weight in 2 months age Fish grow quickly from year 1 to year 3 After one year, the average weight is about 1kg/fish After two year, fish reaches from 3 to 3.5kg/fish Male fish grows faster than female fish (Tran Van Vy, 2005) Fulton fat of fish increases gradually with the weight and the fastest in the early years, males often has a higher fat and they usually decrease as the breeding season (Nguyen Chung, 2007)

2.2.6 Reproductive characteristics

In nature, reproductive season of Striped Catfish starts from May to July yearly Striped Catfish does not breed in culture pond In Vietnam, Striped Catfish does not breed ground in nature Fish breed in Cambodia, fry will be along the stream to Vietnam (Duong Nhut Long, 2004)

In artificial breeding, Striped Catfish can be raised early maturation and spawned sooner than in wild, normally in March Spawning in wild will not get re-development state But in artificial breeding condition, Striped Catfish can be re-reproductive 1-2 times in year (Pham Van Khanh, 2006)

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2.3 The roles of natural food in aquaculture

Natural foods are phytoplankton or zooplankton, benthic animals, microorganisms, organic waste humus Natural foods have many advantages such as small size, suitable for larval mouth size, contain a large amount of free amino acid, the peptic single circuit, unsaturated fatty acid polymer, which contain natural enzyme system can resolve, which provide a full range

of nutrients especially for aquatic animals (Tran Thi Thanh Hien and Nguyen Anh Tuan, 2009)

Fish is able to live and develop in the environment not meet the full range of essential nutrients and especially small fish In the larval stage, fish use completely food from the outside; while the morphology can change a lot, unstable, individual have to find food to survive when the body is too weak

So food plays an important role in the existence and development (Pham Minh Thanh and Nguyen Van Kiem, 2009)

Plankton is the natural food source of the larval stages of many aquaculture species The use of live feed in larval rearing therefore remains a necessity in most aquatic organism hatcheries In fact, most early stages of fish larvae do not react to dry feeds and require live feeds that swim actively and stimulate their omnivorous behaviour In addition, larval fish usually do not ingest or are not able to ingest formulated feeds (Guillaume Drillet, 2012)

In biology, zooplanktons are the second important link behind algae in the natural chain, are direct or indirect food for shrimp and fish, especially in larval stage The development of zooplankton in basin affects to the

development of other species (Tran Suong Ngoc, 2009)

Species: Brachionus angularis (Gosse, 1851)

Brachionus plicatilis (Muller)

Figure 2.2: Some species of rotifer

Rotifers are small, mostly freshwater animals, and are amongst the smallest members of the Metazoa that group of multicellular animals which includes humans, and whose bodies are organized into systems of organs Most of rotifers are about 0.5mm in length or less, and their bodies have a total of around a thousand cells This means that their organ systems are a greatly simplified distillation of the organ systems found in the bodies of the higher animals (Herbert Dartnall, 1978)

In culturing Dwarf Gourami larvae, the rotifers used as starter food significantly improved the growth and survival of Dwarf Gourami larvae (Day

2 – 12) The use of rotifers would enable freshwater larviculture to improve larval performance, increase yield, and facilitate breeding of new fish species with small larvae (Lim L.C, Wong C.C, 1997)

After hatching 45 hours, Micronema bleeker start to nutrient outside Analysing of digestive organ of fish show that Copepoda larvae and rotifer are the most abundant food in the digestive system of Micronema bleeke. It

9

suggests that fish begin eating zooplankton when they start eating outside

(Nguyen Van Trieu, et al., 2008)

Among the 13 species of Brachionus recorded during the present study,

B angularis was the smallest in size The smallest size and its shape may

enable them to be used as suitable live feed for the larvae having small mouth opening, which in turn may lead to higher survival rate and enhanced fish production (Molly Varghese, 2006)

In study about the potential competition and feeding impact of the

common rotifer species, Keratella cochlearis and K quadrata, on the abundant prostomatid ciliates, Urotricha furcata and Balanion planctonicum,

in laboratory batch culture experiments All four species have similar feeding preferences, co-occur in many freshwater environments, and are thus potential

competitors for the same algal food Two small Cryptomonas species served

as food for the ciliates and the rotifers in the experiments Growth rates of each ciliate species were measured when they grew alone and when they were paired with one of the rotifer species Both rotifer species reduced the growth

rate of U furcata, probably primarily by direct feeding on the ciliates Growth rate of B planctonicum was unaffected by K cochlearis, but was drastically reduced by grazing and/or mechanical interference of K quadrata These

results suggest niche partitioning of the sympatric ciliates with respect to their rotifer predators (Thomas Weisse, 2001)

In investigation about distribution of freshwater rotifer Brachionus angularis in Hau river estuary and Can Tho-Hau Giang, in freshwater

ecosystem Brachionus angularis was discovered in flow-water ecosystem as

river or small irrigation canal from 433 to 1,111 ind/m3 (around 5.2 to 17.7%

B angularis/total of rotifers) In low pH water from 4 to 6; B angularis

appeared in rice-field, ponds with density from 3700 to 31,050 inds/m3 and

2.9 to 6.6% B angularis/total of rotifers They were discovered in Hau river

estuary with low salinity (from 1 to 5‰) but no detection in tiger shrimp pond

in high salinity (fron 10 to 15‰)(Tran Suong Ngoc, 2009)

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2.3.2 Copepoda

Figure 2.3 Some species of copepod

Copepods play major role in pond ecosystem, serving as food for small fish, micropredators of fish and other organisms, fish parasite, intermediate hosts of fish parasites and hosts and vectors of human disease Plankton animals, especially rotifers, cladocerans and copapods of the order Cyclopoida are the most important food items in freshwater aquaculture and copepod nauplii are especially valuable for feeding fry Copapods used as natural food are either cultured of collected from natural water bodies (Wojciech Piasecki, 2004)

Reports by Fryer (1957) indicate that Cyclops viridis is predatory;

among 51 guts examined he found approximately 22% with oligochaetes, 18% with cyclopoid copepods, 16% with dipteran larvae, and 6% with cladocerans

These figures suggest that the results obtained with Cyclops viridis and

Simocephalus vetulus may have been atypical since the copepods were forced

to exist on an unnatural diet Another possibility is that not all of animals used

were Cyclops viridis since only a few were sent away for taxonomy

verification

In some areas of Truong Sa Archipelago, study about natural food sources serving aquaculture, zooplankton has variable species (81 species), in which Copepoda has 41 species, accounting for 50.62% with average density 11,775 ind/m3 The density of zooplankton is high in some islands as Sinh Ton, Thuyen Chai, Truong Sa They are a good food source for shrimp and

fish (Nguyen Minh Nien, et al., 2012)

Through a study about assessing biodiversity and spatial of zooplankton communities in the Cu Lao Dung mangrove ecosystem in Soc Trang province, structure of species composition is different, in dry season and rainy season, the density of Copepoda and nauplius larvae are dominant with the ratio 70 -

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71% Zooplankton composition in rainy season is higher than dry season Copepoda reaches the highest in dry season (13 species, 31%) because of a

different salinity between two seasons (Nguyen Thi Kim Lien, et al., 2013)

In a study of investigation suitable food for Copepoda (Microsetella

norvegica) culture Nguyen Thi Kim Lien, et al., (2006) found that mixture

algae consist of Isochrysis gallana, Chaetoceros calcitrans and Dunaliella

tertiolecta with 1:1:1 ratio is the best ration for the development of M Norvegica population on the single ration of each species

In Tam Giang – Cau Hai brackish lagoon system, 43 species of zooplanktons are identified, belonging to 24 genus, 18 families and 3 orders Among them, the Copepod is the most abundant with 37 species and occupies 86.04% The second is the Cladocera with 5 species, accounting for 11.63% and the last is the Rotatoria with 1 species, accounting for 2.33% Families

have the most abundant are Acartidae (Copepoda) with 7 species, accounting for 16.28% The next is Pseudodiaptomidae (Copepoda) with 6 species, accounting for 13.05% Paracalanidae and Pontellidae (Copepoda) are 4

species, accounting for 9.30% (Vo Van Phu and Hoang Dinh Trung, 2012)

In zooplankton composition in Phu Ninh Lake, Quang Nam Province, Copepoda has the highest number with 15 species, accounting for 36.59% The next is Cladocera with 12 species, accounting for 29.27%, Rotatoria has 8 species, accounting for 19.51%, Ostracoda has 1 species, accounting for

2.43% and 5 nauplius, accounting for 12.2% (Vo Van Phu, et al., 2009)

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2.3.3 Cladocera

Figure 2.4 some species of cladocera

Cladocera is a primarily freshwater monophyletic group, an important component of the microcrustacean zooplankton They inhabit most types of continental fresh and saline water habitats, occuring more abundantly in both temporary and permanent stagnant waters Cladocera is an ancient group of Palaeozoic origin Cladocera have about 260 known species but the real number of species is estimated higher 2 - 4 times (L.Forro, 2008)

Most cladocerans are filter feeders, straining water through the setae on

the endites of the limbs Some species of the Sididae (e.g Sida crystallina) and Daphniidae (e.g Simocephalus spp.) attach themselves to vegetation or other substrates while they feed Other cladocerans, such as Scapholeberis

spp., are associated with the water surface film, some swim among the

macrophytes or open water, such as Ceriodaphnia spp., and others, such as

Leydigia leydigi, are benthic The Polyphemidae includes nine predacious

genera, such as Polyphemus pediculus, and have a reduced carapace which

frees the limbs to enable a grasping action (Hutchinson, 1967)

In brackish lakes in Eastern Spain, the microcrustacean community was dominated by cladocerans at Poniente and Levante, by copepod at Reserva, and by ostracods at Múrtulas Numbers of cladocera recorded was much higher at Levante and Poniente and extremely small at Múrtulas Numbers of cladocerans peaked in spring, from March to May, with a second peak in

September at Poniente (Ann Limnol, 2005)

Moina is antennae crustacean group (Cladocera) which is zooplankton components primarily in freshwater aquaculture ponds Moina is commonly used in many different fish species rearing in the period from fry to fingerling like Clariidae, snakehead, Tra catfish, anabas Moina density in ponds is often

to ¾ inch (20 mm) in length quite common Unfortunately, there is very little information concerning practical mass culture methods of Moina, and the available information is in mimeograph documents, foreign journals or other scarce publications (R.W Rottmann, 1992)

In L.Martin’s study, Moina Micrura can replace partially or completely

Artemia Nauplii during early postlaval culture of white shrimp Litopenaeus

schmitti When applying Artemia and Moina in culturing postlarvae white

shrimp Litopenaeus schmitii, it was found that it does not affect survival,

growth rate, protease and α-amylase activities and resistance to osmotic stress

The role of Moina becomes more important in freshwater fish larvae nursery In the stocking process, after moving water from 0.3 to 0.4m depth, drop the eggs and eggs in order to ensure the amount of natural food for fish fry immediately after release into the pond to limit the meat and each of them

As a result of nursery Micronema bleeker, Nguyen Van Trieu (2008)

showed that after 30 nursery days, combining moina and rotifer raised survival rate and growth ability

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CHAPTER 3 RESEARCH METHODOLOGY 3.1 Location

Sample collection was conducted in 3 nursery ponds at Ben Tre Import – Export Joint Stock Company with sizes of:

+ Pond 1: 2,200 m2+ Pond 2: 2,300 m2+ Pond 3: 3,500 m2Sample analysis was conducted at College of Aquaculture and Fisheries, Can Tho University

- Fish fry were sampled for gut analysis with 30 specimens which were randomly collected at each time

- The fish were sampled before stocking, everyday in the first week and 3

days during the rest period

- Fish specimens were then fixed with formalin (3-5%)

3.4.2 Zooplankton sampling

Zooplankton samples were also collected a day before stocking fish and everyday in the first week and every 3 days during the rest period

- The samples were then fixed with 3-5% formalin

3.5 Sample analysing method

- Every sample was counted 3 times with sub-samples The density of zooplankton was calculated by the following equations:

In which:

P: density (inds/m3)

T: total number of individuals counted

A: area of counting square (mm2)

N: number of square counted

Vcđ: volume of sample period to counting (m3

) Vm: volume of water sample filtering through net (m3)

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3.5.2 Fish sample analysis

- Fish were dissected for gut analysis

- Food composition in the gut was identified using frequency and point counting method

+ Frequency method (Hynes, 1950): Stomach contents were examined and the individual food organisms sorted and identified The number of stomachs in which each item occur was recorded and expressed as a percentage of the total number of stomachs examined

Frequency of appearance:

In which:

Ji: number of fish containing prey

P: the number of fish with food in their stomach

+ Point counting method: include 5 steps

Step 1: convention of the foods in stomach

- The smallest size food which was measured in stomach was conventionalised 1 point

- The larger size food was calculated base on the number of standard points

Step 2: combine points and numbers

Call n is the point of sighting food (i) in the stomach

A is combination of points and numbers

Ai = ni x ai Step 3: combine with frequency of food appearance

Call f is frequency of food (i) appearance in stomach

B is the point of food (i) when they are combined with frequency of appearance

Bi = fi x Ai

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Step 4: calculate the total of points of each type of food observed in the stomach (B)

ΣB = Bi + Bii + Biii + + Bn Step 5: calculate the percentage point of the total point of each type of food

3.6 The method for data analysis

The data are calculated on the average value, standard deviation with one-way ANOVA and the means was statistically compared

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CHAPTER 4 RESULTS AND DISCUSSIONS 4.1 Zooplankton species composition

4.1.1 Zooplankton composition in nursery pond

The numbers of zooplankton species collected in Striped Catfish pond were 141 species, belonging to 6 groups including Protozoa (36 species, accounting for 25.53%), Rotifera (56 species, accounting for 39.72%), Cladocera (17 species, accounting for 12.06%), Copepoda (30 species, accounting for 21.28%), Nauplii 0.71% and Insecta 0.71% (Fig 4.1)

4.1.2 Zooplankton composition in the water supply canal

The numbers of zooplankton species collected in water supply canal was

140 species, belonging to 5 groups including Protozoa (36 species, accounting for 25.71%), Rotifera (56 species, accounting for 40%), Cladocera (17 species, accounting for 12.14%), Copepoda (30 species, accounting for 21.43%), and Nauplii 0.71% (Fig 4.2)

Figure 4.1 The percentage of zooplankton species groups in the nursery pond

periods

cannal

4.2 The density of zooplankton composition

4.2.1 The density of zooplankton composition in the ponds

The density of zooplankton varied during 28 nursery days In first two days, the density of zooplankton increased, especially Rotifer, Cladocera, Copepoda, and Protozoa The density of zooplankton began to decrease the end of nursery stage Rotifer was the most abundant group in species number and density They can help to provide essential natural food source, suitable for fry in this stage (Fig 4.3)

The number of zooplankton in each sampling period decreased through time However, in day 5 to day 13, the number of all zooplankton species was quite high Rotifer group (5,728,518 inds/ m3) occupied the highest ratio The next was Nauplii (4,110,556 inds/m3), Copepod (3,965,556 inds/m3),

Cladocera (3,765,926 inds/m3), and Protozoa occupied the lowest ratio (270,372 inds/m3)

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Figure 4.3 showed that nursery pond environment tended to significantly decrease about composition and number of zooplankton species These numbers decreased in last 2 days of nursery stage, only 33 species including 3 species Protozoa, 16 species Rotifera, 7 species Cladocera, 6 species Copepods The density of Rotifer decreased significantly after 2 nursery days The density of Nauplii increased in first 6 days and decreased gradually the end of nursery stage At the end of nursery stage, the density of natural food in pond decreased significantly (<2,000,000 inds/m3) because a large number of natural food was used, recovering and redeveloping of natural food reduced Furthermore, nutritional food source of larger fish such as soy flour, fine bran, egg yolk were no longer, pellets instead, thus nutrition in pond reduced resulting in reduced zooplankton species

4.2.2 The density of zooplankton compostion in the water supply canal

The density of zooplankton in water supply canal varied from 2,778 to 250,000 inds/m3 much lower than in nursery pond The density of rotifer was the highest (250,000 inds/m3) during sampling periods The density of zooplankton in the water supply cannal was ten times lower than in the nursey pond (Fig 4.4) A change in species composition among orders through sampling periods was no significant difference (p>0.05)

Figure 4.4 The density of zooplankton in the water supply canal

50.000

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In Striped Catfish nursery ponds, the water supply canal is inland that is less affect by human management because they are usually effect by fall and down of rise (Bui Ngoc Nhat, 2009) In the dry season, river systems in Chau Thanh, Ben Tre province are alum, so the water supply cannal was effect and decreased the density of zooplankton The water supply cannal usually was poor nutrient and organic matters (Truong Quoc Phu, 2006), so the density of zooplankton was lower than in the ponds

4.3 The zooplankton size in nursery pond

Natural food composition in Striped Catfish nursery pond included 6 groups, such as Protozoa, Rotifer, Cladocera, Copepod, Nauplii, and Insecta

Species belonged to Copepod had higher size than other orders

Skistodiaptomus pallidus belonged to Copepod and Moinodaphnia macleayi

belonged to Cladocera had the biggest size (28,385.15±12,166 and

32,987.57±545.20 µm) Rhabdostyla pyriformis belonged to Protozoa had the

smallest size (77.50±35.00 µm) The size of Nauplii was 715±309.49 µm (appendix C) The size of Rotifer and Nauplii were suitable for fish in few first after finishing yolk sac The size of Cladocera and Copepod were suitable for fish for the next days A shift in zooplankton body size can dramatically affect water clarity, rates of nutrient regeneration and fish abundances (Moore and Folt, 1993)

4.4 Mouth gap size of Striped Catfish in nursery stage

The result showed that mouth gap size of Striped Catfish increased during 28 nursery days In the first day, mouth size of Striped Catfish was from 240.42 to 254.56 µm After 28 of nursery days, mouth size reached from 2,828.427 to 7,071.068 µm (Fig 4.5) Mouth size is one of matters affecting bait catching capacity, especially at the first few days after hatching which affect survival rate and growth rate of the fish

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Figure 4.5 Mouth gap size of Stripped Catfish fry (µm) in 28 nursery days

After finishing the yolk sac, most of fishes used external food in order

to provide nutrition, ensure life activities and development According to Shirota, 1970 (cited by Pham Thanh Liem, 2003) in fry stage, if consider in same species, larger mouth fishes will grow faster than small mouth fishes

During nursery stage, feeding Rotifer in first days was relatively appropriate, because Rotifers have small size depending on species, varying about 100 – 340 µm (Dhert, 1996) Besides, Rotifers have slow swimming feature, suspending in water and may grow in high density, suitable as food for fry stage (Tran Suong Ngoc, 2010) While Moina are much larger in size than Rotifer, the length of adult Moina is 700 - 1,000 µm, approximately two

to three times bigger than adult Rotifers Young Moina (less than 400 µm),

however, are approximately the same size or only slightly larger than adult

Rotifers (Rattmann et al., 1992) Size of mouth fish determine maximum bait

size that they can catch The result showed that after 3 days of hatching, mouth size of Striped Catfish varied from 240.42 to 1,145.51 µm So in first days of nursery stage, Rotifers and Cladocerans were suitable for fry, and Copepod was more suitable for the next days

Table 4.1 Mouth gap size of Striped Catfish in 3 nursery ponds

Ponds Mouth size average

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Table 4.2 showed that there was no significant difference among 3

nursery ponds (P>0.05) The min mouth opening size of Striped Catfish was

240.42 µm The max mouth opening size was from 5,656.85 to 7,071.07 µm

4.5 Natural food composition in digestive tract in 28 nursery days

4.5.1 Frequency of food composition in digestive tract

The result of analyzing natural composition in digestive tract in 28

nursery days showed that appearance frequency of Cladocera reached high

rate in 10 first days of nursery stage, about 8.89 – 88.89% and accounting for

46.44 – 86.68% of total food item in digestive tract From day 13 onward

Copepoda was more abundant (26.67 - 93.33%) and accounting for 27.41 -

48.2% of total food item in digestive tract The amount of natural food reached

high rate in the 16 first days and decrease during nursery period Starting from

day 7, digestive tract of fish contained organic debris because fine pellet was

added and mouth fish size in this time was large enough (1,286.934-1,414.214

µm), so fish could take the pellets

Table 4.2 Frequency (%) and the rate (%) of food composition in

digestive tract with age

Days

Food groups

Organic debris

Notes: day 0: fish after hatching

day 1: stocking fish and fish had yolk sac and not eat outside

I: frequency (%) of food composition digestive tract

II: the percentage (%) of each food item in digestive tract

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In study of Nguyen Thi Hong (2012), in 30 nursery days, the favorite food of Stripped Catfish was rotifer and nauplii in 3, 4 first days and Cladocera in next days Through study results about natural food composition

in digestive tract in 28 nursery days showed that kind of food had high frequency in 10 first days was mostly Cladocera (>80%) Cladocera was one

of the high value natural food providing full of essential nutrition for fish larvae Moina belonging to Cladocera is food source used widely in freshwater fish larval nursery such as carp, ornamental fish,… They contain many

digestive enzymes such as proteinases, peptidases, amylases, lipases and

cellulase, exoenzymes… which are very necessary for larval digestion

(Delbare, 1996) From day 10 and later, Copepod had high frequency (>90%) Copepod provide also rich nutrient natural food source for digestion of fry Copepod has nutrient value higher than Artemia with appropriate ingredient for nutrient demand of larvae Copepod have advantages as high protein content, appropriate amino acid composition and high digestive enzyme, so

Copepod have important role in digestion of larva (Delbare et al.,1996)

Besides, the size of Copepod vary highlied, they could be food of fish larvae

in different stage from nauplius, copepodite to adult Copepoda, so they were suitable for mouth size of Stripped Catfish in this stage

4.5.2 Point counting of food composition in digestive tract

Point of food items will depend on catching times and size of each food item that fish eat The analyzing result of natural food composition in digestive tract of Striped Catfish was showed in table 4.3

Table 4.3 Analysing result of point counting of food composition in digestive tract in 28 nursery stage

Food items Point % Point

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also big size, they always occupied high rate in total amount of food that fish had eaten Although Rotifer had high frequency, size was small, so their point was low

According to frequency and point counting method, Cladocera and Copepod were the two kinds of natural food which had high rate in digestive tract of Stripped Catfish

4.5.3 Combination point counting with frequency of food composition in digestive tract

Combination of two methods (frequency and point counting) analysed natural food composition in digestive tract of Striped Catfish was showed in the following table

Table 4.4 Analysing result of food composition in digestive tract by combination point counting with frequency

Food items Appearance

This result was quite suitable with analyzing result about frequency and point counting method of natural food composition in digestive tract in 28 nursery days It meant that there were no significant differences among three methods

3 to 7, coeffiency of food choice to Rotifer varied from -0.94 to -0.23; Copepoda from -0.54 to -0.15, whereas Cladocera was from 0.53 to 0.95 This showed that in 3 to 7 age days fry did not eat Nauplii but Cladocera was chosen in this stage From day 10 and onward, with the coefficiency of food choice was from 0.57 to 0.97 and 0.18 to 0.81 of Cladocera and Copepod, they

were chosen in this stage

Table 4.5 Coefficiency of food choice of fry in 28 nursery day

The relationship between prey size and mouth size is considered the deciding factor to prey catching capacity of fish (Shirota, 1970, cited by Pham Thanh Liem, 2001) In study of Nguyen Thi Hong (2012), in first two days, fry chose Rotifer and Nauplii with the coefficiencies of food choice were 0.7 and 0.1 But in this study, Nauplii was chosen because the size of Nauplii (715±309.49) fit mouth size of fry in this stage (240.42 - 254.56 µm) and the movement of Nauplii is zigzac, stopping and re-emerging, fry is able to be easy to recognize and catch them (Andersen, 2012) In few later days, Cladocera and Copepod were chosen Because the mouth size of fry was larger and suitable with Cladocera and Copepod size Furthermore, Copepod swims slowly and irregularly and moves zigzac (William and Dennis, 2012) and the movement of Cladocera species is rarely unidirectional and tortuous (Nikolai, 2013) Thus, fish is easy to catch them

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CHAPTER 5 CONCLUSIONS AND RECOMMENDATION 5.1 Conclusions

Zooplankton composition in nursery ponds included main groups as Rotifera, Cladocera, Copepoda, Protozoa, in which Rotifera and Nauplii of Copepoda appeared with high number during nursery stage

Natural food composition in digestive tract of Striped Catfish in 28 nursery days included 6 species: Cladocera, Copepod, Rotifer, Protozoa, Nauplii and organic debris Cladocera usually occupied high rate in 10 first days of nursery stage (46.44 – 86.68%) From day 13 to last Copepoda occupied the highest rate (27.41 - 48.2%)

5.2 Recommendation

- Experimentally investigation on some species of Pangasius such as Basa

Catfish and some freshwater shrimp in order to help to improve survival rate and income for farmers

- Investigation of natural food composition in water environment and in the digestive tract in different brackishwater and freshwater places in Mekong

Delta