Environmental impacts from feeds used in aquaculture systems in the vicinity of mekong river, vietnam

ENVIRONMENTAL IMPACTS FROM FEEDS USED IN
AQUACULTURE SYSTEMS IN THE VICINITY OF THE MEKONG
RIVER, VIETNAM

by

Chau Thi Da

A thesis submitted in partial fulfillment of the requirements for the
degree of Master of Science in
Aquaculture and Aquatic Resources Management

Examination Committee:

Nationality:
Previous Degree:

Scholarship Donor:

Dr. Amararatne Yakupitiyage (Chairperson)
Dr. Wenresti G. Gallardo (Member)
Dr. Hakan Berg (Member)
Dr. Yang Yi (Member)

Vietnam
Bachelor of Science in Agronomy
Cantho University, Vietnam
MOET, Vietnam - AIT Fellowship

Asian Institute of Technology
School of Environment Resources and Development

Thailand
May, 2007

i


ACKNOWLEDGEMENTS
I wish to extend my deepest gratitude to my advisor Dr. Amararatne Yakupitiyage, for
his valuable guidance and constant encouragement, great patience, suggestion and advise
through out the study period. Despite his exceptionally busy schedule, he spares his time and
efforts in going through the research draft, making alterations and giving appropriate verbal
correction. The present shape of thesis would not have been possible without his extensive
guidance and correction.
I wish to express special appreciation and my sincere thans to Dr. Wenresti G.
Gallardo, Dr. Hakan Berg and Dr. Yang Yi as members of examination committee for their
valuable guidance, constant encouragement, great patience, and valuable suggestions. Thanks
are due to my wife, Ms. Thai Huynh Phuong Lan, who showed me numerous ways to improve
my English expressions in this thesis.
I am grateful to Ministry of Education and Training, Vietnam and An Giang University
Vietnam for its awards of the Masters scholarship. I also sincere thanks to
Dr. Nguyen Thanh Phuong, Dr. Truong Quoc Phu (Department of Aquaculture and Fisheries –
Can Tho University, Vietnam) and Mr. Nguyen Thanh Son, Mr. Bui Xuan Thanh, Mr. Nguyen
Minh Du and my fellow students Mr. Nguyen Long Doat Quoc, Mr. Nguyen Minh Ngoc and
Mr. Nguyen Ngoc Lan in Department of Agriculture & Natural Resource, An Giang
University Vietnam) for their valuable help during this thesis.
Last but not least, this work is dedicated to my parents and family members for their
love, patience, encouragement and moral support to complete my study in AIT. I would like to
thank to all of my classmates for their support during this study.

ii

ABSTRACT
This study was conducted in My Hoa Hung village in Long Xuyen city, An Giang
province, Mekong River in Vietnam during August to December 2007, to assess
environmental impacts from feeds used in aquaculture systems such as intensive fish cages,
pens and ponds culture on and in the vicinity of Mekong River, Vietnam (e.g. Pangasius
Hypopthalamus, Colossoma macropomum species). Moreover, the purpose of this study is to
investigate the effects of feeds in the intensive aquaculture systems towards water
environment. The study was commenced by a field survey of twenty Pangasius
hypophthalmus cage farmers, 18 Pangasius hypophthalmus pond farmers, 20 Pangasius
hypophthalmus pen farmers and 15 Colossoma macropomum cage farmers. The survey
showed that the fish culture in An Giang province was developed and operated by farmer’s
indigenous knowledge. The fish density is quite high of 80-105 fish/m2 as compared with the
optimum range of 30-60 fish/m2. There are three kinds of popular feeds such as homemade,
pellet and Pangasius waste used in this area. The pellet feed is more effective in terms of
economic profit, less environmental pollution, better product quality and reduction in trash
fishes from nature. Among three of culture systems, pen culture has more economic benefits
because this system is separate from other systems. It is located in the alluvial grounds with
high water turnover so that fish is not affected by disease transmission from other farms.
Water quality of the river is still in the limit for fish culture in three surveyed months of
August, October and December. Nitrogen and phosphorus concentrations of October are
lowest because this time is the peak up of flooding season. In this study the adverse effects of
fish culture is not revealed clearly due to the survey carried out in the rainy season.

iii


Table of Contents
CHAPTER TITLE

Title Page
Acknowledgements
Abstract
Table of Contents
List of Tables
List of Figures

PAGE
i
ii
iii
iv
vi
viii

1

Introduction
1.1 Introduction
1.2 General objective
1.3 Specific objectives

1
1
2
2

2

Literature Review

2.1 Basic biology of Pangasius hypopthalamus
2.2 Wild populations
2.3 Source of seed stock
2.4 Brood stock and rearing conditions
2.5 Fish culture systems in An Giang province, Mekong River in
Vietnam
2.6 Production statistics
2.7 Feeds and Feeding
2.8 Nutrient requirements of Pangasius hypopthalamus
2.9 Environmental impacts
2.10 Basic biology of Colossoma macropomum

3
3
5
6
7
7
11
12
14
15
17

3

Material and Methods
3.1 Steps of the study
3.2 Socio-technical survey
3.3 Laboratory studies

3.4 Assessment and comparison of the different systems
3.5 Data analysis
3.6 Assessment of effluent and feed waste contribution

19
19
19
23
29
29
29

4

Results and Discussion: Survey of aquaculture systems in An Giang

34

province

4.1
4.2
4.3
4.4
4.5
5

General information
Socio-economic survey
Technological survey of aquaculture systems

Costs and return benefit analysis (1 US$ = 15,000 VND)
Strength (opportunity), constraints and environmental awareness

Results and Discussion: Assessments of contribution of feed waste used
in aquaculture systems and water quality parameters
5.1 Introduction
iv

34
36
40
53
57
60
60


5.2
5.3
5.4
5.5

6
7
8
9

Materials and methods
Results
Feed utilization efficiency

Amount of nitrogen (N) and phosphorous (P) in the waste loading
from feeds used into the river
5.6 Discussions
Conclusions
Recommendations for future study
Reference
Appendixes
Questionnaire
Appendix A: Socio-technical aspects of aquaculture systems
information
Appendix B: Economic aspects of aquaculture systems information
Appendix C: Water quality parameters of aquaculture systems in
An Giang province, Mekong River in Vietnam
Appendix D: Water quality parameters in aquaculture systems in
three seasons

v

60
61
70
71
73
76
77
78
84
84
95
100

102
105


List of Tables
TABLE No TITLE

PAGE

2.1

Estimated numbers of Pangasius hypophthalmus fry caught in the dais fishery in
Viet Nam
6

2.2

Status of Pangasius hypophthalmus pond culture in An Giang province

10

2.3

Aquaculture using trash fish (Edwards, 2004)

13

3.1

Parameters and analysis of feed

25

3.2

Samplings were carried out on three seasons in area selected

26

3.3

Parameters and analysis of water quality

27

4.1

Average age of fish farm manager in An Giang province

37

4.2

The distribution (%) of educational level of fish farming managers in An Giang
province
38

4.3

Farming experience of fish managers in An Giang province (%)

38

4.4

Training times for fish manager (%)

39

4.5

Total water volumes and total area of aquaculture systems in An Giang province

44

4.6

Production season of Pangasius hypophthalmus in An Giang province

44

4.7

Stocking densities in aquaculture systems in An Giang Province

45

4.8

Ingredients of homemade feed for Pangasius hypophthalmus species and

percentage of farmers in An Giang
47

4.9

The ratio % materials in homemade feed used by household’s fish cage

4.10

Ingredients of homemade feed used for Colossoma macropomum species and
percentage of farmers in An Giang province
48

4.11

Variable costs of production unit of aquaculture systems in An Giang province

54

4.12

Net return of fish farmers in An Giang province

55

4.13

The percentages (%) of name of buyer in Mekong Delta, in Vietnam

57

5.1

Water level water level Hmax (m) in Tan Chau district of An Giang province and
Can Tho province in years having great floods
61

5.2

Water temperature (T0C) in aquaculture systems in three seasons

62

5.3

pH levels in three seasons of aquaculture systems in An Giang province

63

5.4

DO in aquaculture systems in three seasons

64

vi

48

5.5

TSS in aquaculture systems in three seasons

65

5.6

Nitrite-N (NO2) and nitrate-N (NO3) in aquaculture systems in three seasons

66

5.7

Total nitrogen in aquaculture systems in three seasons

68

5.8

Total nitrogen in aquaculture systems in three seasons

69

5.9

Fish yield (tons/crop/culture unit) and FCR in relation to feed and feeding level
used in aquaculture systems
71

5.10

Feed consumed and fish biomass in dry matter related to waste material uneaten
feed and metabolize (tone/crop/culture unit)
72

5.11

Fish carcasses (adult fish) and feeds compositions analysis

5.12

Amount nitrogen (N) and phosphorous (P) (tons) content in feed used, fish
biomass and waste material in uneaten feed in different culture systems
73

vii

72


List of Figures
FIGURES No

TITLE

PAGE

2.1

Aquaculture timeline for both cage and pond production in Vietnam

8

2.2

Annual production of cage culture in An Giang and Dong Thap provinces

9

2.3

Proportion of different catfish species in the Mekong Delta in cage production

9

2.4

Annual production of Pangasius hypophthalmus spp for export in the Mekong
Delta, Vietnam
12

3.1

Study Area Map of An Giang Province, Mekong Delta, Vietnam

3.2

Top view of sampling site at the Pangasius hypophthalmus cage and Pen
culture

28

3.3

Top view of sampling site at the pond culture

3.4

General view of the field measurement at My Hoa Hung, Long Xuyen city, An
Giang province
28

3.5

Mass balances for phosphorus and nitrogen load from cage and pen fish
farming
30

3.6

Nutrient budgets of cage, pen and pond

31

3.7

Nutrient budgets of cages in the river

31

4.1

Average ages of fish farmer’s manager in An Giang province

37

4.2

Percentage gender distribution of fish farmer’s manager in An Giang province

37

4.3

Previous occupation of fish farm owner in An Giang province

39

4.4

Cages culture in An Giang province, Mekong River of Vietnam

40

4.5

Pen culture in An Giang province, Mekong River of Vietnam

42

4.6

Pond culture in An Giang province, Mekong River of Vietnam

43

4.7

Kinds of feed used in Pangasius hypophthalmus culture systems

46

4.8

The percentages of fish farming using different ingredients of homemade feed
for Pangasius hypophthalmus species in An Giang
47

4.9

The percentages of fish farming using different ingredients of pangasius waste
feed for Colossoma macropomum cage culture
49

4.10

Diagram of feed processing for Pangasius hypophthalmus species

50

4.11

Diagram of feed processing for Colossoma macropomum species

50

4.12

Pangasius hypophthalmus feed processing

51

viii

20

28


4.13

Colossoma macropomum feed processing

51

4.14

The ratios of fish farming using the additives in homemade feed

52

4.15

Average initial instruction cost of fish culture systems in An Giang province

54

4.16

The structure of the marketing of channel of fish aquaculture in the Mekong
River, Vietnam
56

5.1

General comparison views of water quality parameters in Cages, Pens and
culture
60

5.2

General comparison views of water quality parameters in Ponds culture

5.3

Water temperatures in upstream and downstream of cages and pens culture
compared to pump-in and pump-out of ponds culture during three seasons
62

5.4

pH levels in upstream and downstream of cages and pens culture compared to
pump-in and pump-out of ponds culture during three seasons
63

5.5

DO in upstream and downstream of cages and pens culture compared to pumpin and pump-out of ponds culture during three seasons
64

5.6

TSS in upstream and downstream of cages and pens culture compared to pumpin and pump-out of ponds culture during three seasons
65

5.7

Nitrite-N (NO2; mg/L) concentrations in upstream and downstream of cages
and pen culture compared to pump-in and pump-out of ponds culture during
three seasons
67

5.8

Nitrate concentrations at upstream and downstream of cages and pens culture
as compared with pump-in and pump-out of ponds culture during three seasons 67

5.9

Total nitrogen in upstream and downstream of cages and pens culture as

compared with pump-in and pump-out of ponds culture during three seasons
68

5.10

Phosphorous concentrations in upstream and downstream of cages and pens
culture as compared with pump-in and pump-out of ponds culture during three
seasons
69

ix

60


CHAPTER 1
INTRODUCTION
1.1

Introduction

In recent years, aquaculture production has increased worldwide, mainly due to the
increasing demand for aquaculture produce, and the need for new food supplies. This
development generates profit and income, but it also bears risks of negative environmental
impact, such as pollution or biodiversity change (Tovar and Moreno, 2000). The main
input in most intensive fish culture systems is feed of fish in the form of wet homemade
feed, trash fish, and pellets. These feeds are partly transformed into fish biomass and partly
released into the water as suspended solids or dissolved matter such as carbon, nitrogen
and phosphorus. These wastes are originating from surplus food, faces and excretions via
gills and kidneys. Other pollutants are residuals of drugs used to cure or prevent diseases.

Aquaculture feeds and feeding regimes can play a major role in determining the
quality and potential environmental impact or not of finfish and crustacean farm effluents
(Tacona and Forster, 2003). This is particularly true for those intensive farming operations
employing open aquaculture production systems, the latter including net cages/pens
enclosures placed in rivers, estuaries or open-water bodies, raceway or pond production
systems. This is perhaps not surprising since the bulk of the dissolved and suspended
inorganic and organic matter contained within the effluents of intensively managed open
aquaculture production systems are derived from feed inputs, either directly in the form of
the end-products of feed digestion and metabolism or from uneaten/wasted feed, or
indirectly through eutrophication and increased natural productivity.
An Giang province of Vietnam is one of the provinces in Mekong Delta where
many types of intensive fish culture systems i.e. fish pond, floating cages and pens, are
located. An Giang province located on the border to Cambodia is the centre of production
(70 to 80 %) of Vietnamese’s Pangasius gigas (Basa fish), Pangasius hypophthalmus (Tra
fish) come from this region (FAO, 2005). The number of floating cages in the province
increased from 169 in 2003 to 3,568 in 2004 but 3,531 in 2005 decreased 37 pieces. There
were 1,167 ha of fish ponds area in 2004 and 1,512 ha of fish ponds area in 2005. Overall
production capacities from these systems were 152,507 tons in 2004 and 232,139 in 2005
(An Giang province statistical yearbook, 2005). Mainly Pangasiusis hypophthalmus (Tra
fish) are cultured in floating cages and pens in rivers and canals in An Giang province. The
total water area for pens culture and Veo (hapa net) culture for this species were 21 and 80
ha, respectively, in 2003 and the area increased up to 32 and 84 ha, respectively, by 2004
and 313 ha in 2005 (An Giang province statistical yearbook, 2005). The total number of
floating cages in total of province increased from 2,126 in 1995 to 3,568 in 2004. These
increasing trends might have continued until today.
Intensive floating cage and pen culture of Pangasius hypophthalmus (Tra fish) have
been developed and operated by the indigenous knowledge of local farmers (Tan, 2001)
which provides a new significant income source, helping to diversify farming activities,
reduce risk, alleviate poverty and provide employment opportunities throughout the year.
This is very important livelihood activity for landless farmers.

Floating cage and pen culture in rivers is an intensive operation by nature, have
both detrimental and beneficial effect on surrounding environment. The major problem
areas in river floating fish culture systems are 1) Environment interaction i.e. effluent from

1


this culture disposed of throughout the water body and thus causes a deterioration in the
surrounding environmental quality. 2) The farmers of An Giang province in and all
Mekong delta are facing lack of Pangasius (Basa fish, Tra fish) fingerling to culture many
years ago due to over exploitation fry natural resource. 3) Over use of feed and wet
homemade feed such as (Pangasiusis waste, pelleted feed and wet homemade feed) are less
stable than manufactured feed, and typically has a higher feed conversion ration than
manufactured feed, thus the use of homemade feed can also lead to increased water
pollution (Edwards 2004). 4) Outspread diseases and the excessive use of antibiotics in
catfish cultivation which is a major problem for the farmers of An Giang province.
Therefore, this study was carried out detailed study on fish culture that release
effluents and waste to rivers to find ways to reduce negative impacts to the aquatic
environment. The study was focuses on Pangasius hypophthalmus (Tra fish) and
Tambaqui fish (Colossoma macropomum) floating cages, ponds and pens culture to assess
of technical, environmental and economical factors with a special emphasis on fish feeds
use. Finally, it is expected to develop recommendations for sustainable development and
management of floating cages and pen culture of Pangasiusis. hypophthalmus, Tambaqui
fish (Colossoma macropomum) and others fish species in rivers An Giang province,
Vietnam.
1.2

General objective

The general objective is to assess the feed use in aquaculture systems on and in the

vicinity of Mekong River and environmental impacts caused by fish feeds use in these
pond, cage and pen culture systems in the Mekong River, South Vietnam.
1.3

Specific objectives
1. To assess and compare the technical, economical, and environmental aspects of
selected pond, floating cage and pen culture systems in An Giang province.
2

To assess and compare the feed use in these systems e.g. Pangasius hypophthalmus,
Colossoma macropomum species.

3. To assess and compare the feed waste contribution from there different culture
systems.
4. To develop recommendations for sustainable management of pond, cage and pen
culture in the vicinity of Mekong River, Vietnam.

2


CHAPTER 2
LITERATURE REVIEW
2.1

Basic biology of Pangasius Hypophthalamus

General biology of fish:
Phylum Vertebrata
Class Teleostomi
Order Cypriniformes

Family Pangasiidae
Genus Pangasius
Species Pangasius hypophthalmus Sauvage, 1878
Pangasiid species are important for commercial fisheries and aquaculture in
Vietnam, Cambodia, Thailand, and Indonesia. The taxonomy of this family has been
recently reorganized into four genera and 25 species (Vidthayamon and
Roongthongbaisree, 1993). Several of these species (Pangasius bocourti, Pangasius gigas,
Pangasius hypophthalmus, Pangasius larnauddii and Pangasius sanitwongsei) have
economical potential for aquaculture but today the three species of Pangasiid (Pangasius
hypophthalmus, Pangasius larnauddii, Pangasius gigas) are very popular and the most
famous in Mekong River in the Southern Vietnam, Vietnam language called these above
species are Pangasius hypophthalmus (Tra fish) and Pangasius bocourt (Basa fish) but the
English common name is “Striped catfish”.
Pangasius hypophthalmus (Tra fish) and Pangasius bocourt (Basa fish) are two of
28 species in the family Pangasiidae, of which the majority, including Pangasius
hypophthalmus (Tra fish) and Pangasius bocourt (Basa fish), are in the genera Pangasius.
Pangasiidae species are found primarily in freshwater in countries surrounding the Indian
Ocean basin; the largest concentration of Pangasiidae diversity is found in Southeast Asia
(Roberts and Vidthayanon 1991; Gustiano, 2003). Both Pangasius hypophthalmus (Tra
fish) and Pangasius bocourt (Basa fish) are native to Cambodia, the Lao People's
Democratic Republic (Lao PDR), Thailand, and Viet Nam.
Knowledge of the biology and ecology of Pangasius hypophthalmus (Tra fish) and
Pangasius bocourt (Basa fish) in the wild is scarce (Hung, 2003). Both species are
omnivorous, and feed primarily on plant matter, fruits, and some mollusks sometimes have
seen small fish (Vidtayanon, 1993); Pangasius bocourti (Basa fish) consumes more fish
and crustaceans than Pangasius hypophthalmus (Tra fish) (Poulsen, 2004).
The natural range of Panagius hypophthalmus (Tra fish) is limited to the lower
Mekong Basin, which includes Cambodia, Lao PDR, Thailand, and Vietnam, and the Chao
Praya River in Thailand (Roberts and Vidthayanon, 1991; Poulsen, 2004). In the Mekong
River, upstream migration of adult Panagius hypophthalmus (Tra fish) begins in annual

year in November when the water level in the river decreases and continues well into the
dry season, at least until February. In the late dry season, or the start of the monsoon
season, a downstream migration takes place from Khone Falls on the Lao PDR-Cambodia
border to the Mekong Delta (Rainboth, 1996; Sokheng, 1999; Kottelat 2001; Poulsen,
2004). During the dry season, deep pool habitats serve as important refuge for adult
Pangasius hypophthalmus (Tra fish), while during the rainy season, the flood plains and

3


tributaries provide prime feeding habitat (Poulsen, 2004). Sexual maturity of Pangasius
hypophthalmus (Tra fish) in captivity occurs at around more than 3 years of age 4 kg and
total length of 54 cm in nature, (Van Zalinge, 2002) but the good fecundity for this species
at 5-6 years old, although there is no documentation of maturity for Pangasius
hypophthalmus (Tra fish) in the wild (Van Zalinge, 2002). Female of Pangasius
hypophthalmus (Tra fish) each produce about 100,000 eggs per kilogram (kg) of body
weight and spawn up to four times per year. After spawning, the early larval stage of
Pangasius hypophthalmus (Tra fish) drift downstream with the water current and
eventually enter rearing and feeding habitats on the river’s floodplains (Poulsen et al.
2004).
Pangasius hypophthalmus (Tra fish) is one of the largest catfish in the Mekong
River and can grow up to a maximum weight of 70 kg in nature (IG Baird, personal
communication). It is very common, commercially important and intensively exploited in
the Lower Mekong River and has been widely introduced for aquaculture in Southeast
Asia (Roberts and Vidthayanon, 1991; Rainboth, 1996).
(Pangasiid catfishes and cyprinids; Poulsen and Valbo-J_rgensen, 2001; Baird and
Flaherty, 2004) make vast migrations between the low to middle basin feeding grounds and
upper basin spawning grounds, often located in upland middle-sized river branches.
Similarly, the sutchi catfish, Pangasius hypophthalmus (Tra fish) (Sauvage, 1878)
(Pangasiidae, Teleostei), a long-distance migratory catfish occurring in large rivers of the

Mekong and Chao Phraya basins, exhibits an annual pattern of migration between feeding
and spawning grounds. It spawns in the upper stretches of the Cambodian Mekong River
between the Khone Falls on the Cambodian/Lao border and the town of Kratie from May
to August (Poulsen and Valbo, 2001) (from The discontinuous spawning habitat consists of
rapids and sand banks interspersed with deep rocky channels and pools (Van Zalinge,
2002). It covers about 1% of the feeding area (52,500 km2), which is located in the huge
floodplain of Tonle Sap, central and southern Cambodian lower Mekong and the
Vietnamese Mekong delta. After spawning, adult fish migrate back to the feeding grounds
(consisting of inundated forests and other vegetation) and larvae drift to the nursery
floodplains located close to the feeding grounds. From this point of view, the river basin
constitutes one ecological unit interconnecting upstream spawning habitats with
downstream rearing habitats.
Some differences between of Pangasiusis species studied: Pangasius
hypophthalmus (Tra fish) is the predominant finfish produced in the Mekong Delta region
(Phillips 2002). P. gigas (Basa fish) is produced at much lower levels due to the fact that it
is less hearty, grows slower, and is more expensive to produce (Edwards, 2004). The
fecundity of Pangasius gigas (Basa fish) is also up to 10 times lower than that of
Pangasius hypophthalmus (Tra fish), and Pangasius gigas (Tra fish) has a much lower
tolerance for poor water quality than Pangasius hypophthalmus (Tra fish) (Pers. Comm.,
Philippe Cacot, 2005).
In addition to a lower production cost of Pangasius hypophthalmus (Tra fish) also
has a higher dress-out weight than Pangasius gigas (Basa fish); 3.1 kg of Pangasius
hypophthalmus (Tra fish) are required to produce a 1 kg fillet, whereas 3.7–3.8 kg of
Pangasius gigas (Basa fish) is required to produce the same sized fillet (Edwards, 2004).
Pangasius gigas (Basa fish) was, at one time, the primary fish for export to Asian markets,
as Pangasius hypophthalmus (Tra fish) was thought to be dirty and of poor quality. Due to

4

the ease of production Pangasius hypophthalmus (Tra fish) aquaculture was cleaned up
and export of Pangasius hypophthalmus (Tra fish)) has increased under the name of
Pangasius gigas (Basa fish). True Pangasius gigas (Basa fish) is still preferred locally, and
will sell for one third more than Pangasius hypophthalmus (Tra fish). The Pangasius gigas
(Basa fish) that is exported goes to a specialty market (Pers. Comm., Philippe Cacot, 2005).
2.2

Wild populations

Over their native range, Pangasius hypophthalmus (Tra fish) stocks are divided into
two distinct populations: stocks in the Mekong River in Cambodia and Viet Nam belong to
one population (southern stock); and stocks above Khone Falls in Lao PDR and Thailand
form a separate population (northern stock) (Van Zalinge, 2002 and Poulsen, 2004). The
southern Vietnam’s stock is subject to more intense fishing than the northern stock, and is
larger in size (Poulsen, 2004).
Pangasius hypophthalmus (Tra fish) has been spread more widely outside its native
range than Pangasius gigas (Basa fish). It has introduced to China, the Philippines, Taiwan,
Indonesia, Malaysia, Guam, Bangladesh, and India primarily for the purpose of
aquaculture (Van Zalinge et al. 2002; Pers. Comm., Philippe Cacot, 2005). There is no
evidence of self-sustaining populations of Pangsius hypophthalmus (Tra fish) escaping
from these aquaculture operations or negative ecological impacts from these operations
thus far.
The commercial fishery for Pangasius hypophthalmus (Tra fish) fry is relatively
new, with collection beginning in the early 1980s. There is a general thought that wildcaught fry are better quality than hatchery-reared fry (Trong, 2002). The dais fishery
exhibits high seasonality, with peaks in early June, coinciding with the May-August
spawning period (Van Zalinge, 2002). In the upstream areas of the Mekong delta, there are
plenty of natural resources, good environment conditions and low labour cost and available
for Pangasius in the pond, floating cage and pen culture. Ministry of fisheries, cited by
Khanh 1996 in Vietnam, the early in the monsoon season, wild adult river catfish migrate
out of the Great Lake and go down the Tonle Sap River, before swimming up the Mekong

River delta to spawn below the Khone Falls on the Lao-Cambodian border, which has
suitable environment conditions for gonad development and breeding. Traditionally, river
culture systems in the South of Viet Nam relied entirely on wild caught fry for cages
culture, ponds culture and pens culture. Size and colors of fry into three categories, which
are 1.3-1.5 cm, 1.5-1.7 cm, and 1.7-2.0 cm, or silver, pink and black, respectively
(Department of Freshwater Fisheries 1977; Department of Agriculture of An Giang
province 1977; Tien 1995; cited by Khanh 1996), classify Fry. In addition to being caught
in the dais fishery, Pangasius hypophthalmus (Tra fish) are taken in other small but
important fisheries by gillnet, hook-and-line gear, seines, trawls, and, to a lesser extent,
traps and stunning with explosives. Fortunately, extensive education programs have led to
a decline in the use of explosives in recent years.
In Vietnam, recent success in Pangasiid breeding (Pangasius hypophthalmus and
Pangasius boucourti) has led to more farmers stocking hatchery-reared catfish, although
some farmers still prefer wild-caught seed. Increasingly in the Mekong Delta, Pangasiid
are coming from hatcheries, as demand for post-larvae rise. Whether this is because of
diminishing wild supply, or high demand, or a combination of both, is not know. From

5


limited information available, there appears to be no evidence that juvenile collection is a
wasteful use of the resource, although other species are discarded in the process.
2.3

Source of seed stock

Supply of seed stock for Pangasius hypophthalmus aquaculture has traditionally
been dependent on collection of wild fingerling of Pangasius spp. fry from rivers (Cacot,
2003; Edwar, 2004). Most of the spawning grounds for both Pangasius hypophthalmus
(Tra fish) and P. bocourt (Basa fish) are located within the borders of Cambodia (Poulsen

et al, 2004). Fishers usually target Pangasius hypophthalmus (Tra fish) fry; however, they
are often unable to identify fry at the species level and some fish farmers have reported a
mixture of Pangasius species in their ponds. In the wild fishery, non-Pangasius species are
thrown back or used as fish feed (Bun 1999; Van Zalinge, 2002); an estimated 5 – 10 kg of
fish of species other than Pangsius hypophthalmus (Tra fish) are killed for each kilogram
of river catfish fry caught (Phuong, 1998). The fishery for river catfish fry was outlawed in
Cambodia in 1994 and in Viet Nam in 2000, but continues illegally, still supplying fry to
aquaculture (Bun 1999; Van Zalinge, 2002). It is unclear the extent to which this practice
is still in use; however, the increase in hatchery production and enforcement indicates that
capture of wild river catfish fry is declining; a 1000 - fold decrease in wild-caught fry has
been observed in the An Giang province, Viet Nam (Van Zalinge, 2002).
Anecdotally, the number of wild-caught fry has dropped to almost zero, with
hatchery fry dominating the supply to aquaculture operations (Pers. Comm., Kwei Lin,
Asian Institute of Technology, 2005). There are many small scale nursery hatcheries for
Pangasius species fry in Viet Nam (< 1 ha in area) that now provide seed stock to
Vietnamese river catfish farms. These hatcheries produce enough fry for the local market
and for export to Cambodia (Edwards, 2004). The first artificial propagation of Pangasius
spp. catfish occurred in Thailand in 1959 and has since expanded throughout Southeast
Asia (Trong, 2002). In 1999, more than 270 million (Pangasius hypophthalmus and
Pangasius boucourti) fry and fingerlings were produced by a number of state and private
hatcheries (Van Zalinge, 2002).
Table 2.1 Estimated numbers of Pangasius hypophthalmus (Tra fish) fry caught in the dais
fishery in Viet Nam.

6


2.4

Brood stock and rearing conditions

Successfully for breeding Pangasius hypophthalmus and Pangasius boucourti by
Cacot, Muon and Trieu in 1996; Experiments were conducted with brooders raised in
floating cages on the Mekong River close to the town of Chau Doc in An Giang province,
Vietnam. Male brooders were about 8 years of age, with a body weight ranging from 3.3 to
6.9 kg. Wood and net cages (50 m3, 6m x 3m x 2.8 m depth) were used for stocking
brooders at low density (1.1 fish m3). Brooders were fed with moist pellets (35% moisture)
prepared with 33% fish meal, 33% rice bran and 33% C50 Proconco industrial concentrate,
including vitamins and mineral premix. Water was added (30% total) but cooking was not
necessary as the industrial concentrate provided suitable stickiness. The pellets contained
42% proteins, 12% lipids and 7% carbohydrates (% dry matter). Food was provided twice
a day at a daily feeding rate of about 1% of the fish biomass (based on the weight of crude
ingredients without water added).
2.5

Fish culture systems in An Giang province, Mekong River in Vietnam

Methods of culture vary widely from simple subsistence ponds to large,
industrialized Pangasius hypophthalmus ponds. Commercial production of river catfish
occurs either in earthen ponds, floating cages and pens culture in natural water bodies
(Hung, 2003). The major culture systems in recent years in An Giang province are
intensive pond culture, intensive floating cage and pen culture.
2.5.1

Pond culture

Pond aquaculture of river catfish (Pangasius hypophthalmus) has been a tradition
in the Mekong Delta and River Basin for several hundred years. Before more
technologically advanced methods were introduced in the 20th century, farmers in Vietnam
integrated systems of gardens, ponds, and livestock quarters for combined agriculture and

aquaculture, a method known in Viet Nam under the acronym VAC (Edwards, 2004).
Pond culture is the predominant method for producing Pangasius hypophthalmus
(Tra fish) this area in 1999, at nearly ten-fold the production area of the next most common
method. Other common aquaculture methods for Pangasius hypophthalmus (Tra fish)
include floating cage culture, ditch culture, and rice-paddy/field culture (Hung, 2003 and
Edwards, 2004). Most farms in the Lower Mekong Delta are small-scale, while farms in
the Bassac River of Cambodia in the Mekong Delta are large cage-culture operations
(Phillips, 2002). In Lao PDR, Thailand, and Viet Nam, river catfish (Pangasiidae)
aquaculture operations use more pond culture than cage culture.
Farmers collaborating in the last ten years with the Rural Extension for Aquaculture
Development (READ) Project in the Mekong Delta area have stocked river catfish
(Pangasiid) in poly-culture with 11 other fish species, including common carp, silver carp,
Indian carp and silver barb. These are stocked in different proportions, depending on the
agro-ecological zone, the availability of on-farm feeds and the socio-economic status of the
household (READ in 1998, 1999 and 2000). Because they low dissolve oxygen (air breath)
and can tolerate poor water quality, Pangasius hypophthalmus (Tra fish) are often stocked
at densities as high as 20-25 fish/m2, in both monoculture and poly-culture systems.
Information of Pangasius hypophthalmus (Tra fish) ponds culture in An Giang recorded:
Pond size from 100 m2 to 7,000 m2; Stocking density and size: 40 fish/m2; 20 g/fish; 40%

7


water exchange/day; Harvest size 1.1 kg/fish; Survival: 90%; Yield 360 tonnes/7 months;
FCR = 1.4 – 1.6; Farm gate price: 14,000 VND/ kg (Amara, 2006)
The production cycle of Pangasius hypophthalmus (Tra fish) comprises one single
cycle in grow-out ponds (Figure 2.1). Fish are usually fed rice bran, broken rice, kitchen
scraps and vegetables. In addition, river catfish feed on natural feed, which develops in
ponds fertilized by animal wastes, including those of pigs and humans. Fish from
integrated pond systems often have a muddy off-flavor and the flesh is always darker in

color than the flesh of river catfish reared in cages. Consumers and the export market in
particular, prefer the white colored flesh of Pangasius hypophthalmus (Tra fish) reared in
cages.
Hatcheries

Catching wild fry
(10-12 days old)

Larvae-rearing in earthen ponds

Growth-out in ponds

Advance fingerling growth
in the cages (1-2 months)

Growth-out in ponds

Source: Hung & Cacot, 2000

Figure 2.1 Aquaculture timeline for both cage and pond production in Vietnam
Pond culture tends to use less advanced technology than cage culture, and pond
culturists tend to use a higher proportion of wet homemade feeds as well as depend on
natural feeds in ponds that are fertilized with animal wastes and poly-culture with other
fish species, such as carps, Nile tilapia (Oreochromis niloticus), and kissing gourami
(Helostoma temmincki)… These practices tend to give farmed fish’s meat a muddy flavor
and flesh yellowish color. These characteristics are not favored by international markets,
thus cage aquaculture is the preferred method of operation for fish being produced for
export (Trong, 2002). Despite the higher risks of high stocking densities and poor water
flow, which lead to such undesirable characteristics as yellow flesh, pond culture
constitutes 50% of total river catfish aquaculture in Southeast Asia (Cacot, 2004).

2.5.2

Cage culture

Cage culture started nearly a century ago in Cambodia (Chevey and Poulain, 1940;
Coche, 1978; cited by Hung and Cacot, 2000). It was introduced to Viet Nam when
Vietnamese refugees fled Cambodia in the 1960s (MRC 1992). Since then, cage culture
has continued to develop and is concentrated along the Vietnamese-Cambodian border in
An Giang and Dong Thap provinces in Viet Nam (Phuong, 1998). (Figure 2.2 and 2.3)
shows cage production from 1985 to 1995 for An Giang and Dong Thap provinces in
Mekong Delta.

8


Figure 2.2 Annual production of cage culture in An Giang and Dong Thap provinces

Figure 2.3 Proportion of different catfish species in the Mekong Delta in cage production
These are literally floating cages (floating houses). Each floating house has a
worker that lives on the structure full-time. It costs less than US$ 12,000 to build one of
these using local materials. This structure is a perfect example of the industrious nature and
ingenuity of the Vietnamese people. It is not high technology, but is extremely effective at
producing fish. Floating cage culture systems are used for both Pangasuis gigas (Basa fish)
and Pangasius hypophthalmus (Tra fish); use of one system over the other depends on the
country. Fry are wild-caught or hatchery-reared, and kept in ponds until the grow-out stage.
Stocking density and size: 50-60 fish/m2; 20 g/fish, fish reach marketable size at 1 – 1.5 kg
(Hung, 2003) after about 6 to 8 months of culture, starting from fingerlings (approximately
2 months of age) (Edwards, 2004). Feeds and feedings used for floating cage and pen
culture in An Giang province which have catfish wash used to Pangasiusis fish specie, wet
homemade feed, pellet feed. Farm made wet-feed is widely used for example; mix 40%

rice bran + 10% soybean meal + 50% fish meal and FCR: 1.8 – 2.0.
Floating cage (floating house) culture is the most famous in An Giang province and
it is an intensive culture system since fish are stocked at very high densities (100 kg/cum)

9


and artificial feed is provided as the only nutrient source for fish growth. Pangasius
bocourti (Basa fish) is the main species cultured in cages, contributing 85 percent of the
total floating cages production in the Mekong delta. Other Pangasiids contribute 6 percent
of total cages production in Vietnam. Floating cage culture development is concentrated in
An Giang and Dong Thap provinces in areas with suitable water currents and locally
available supplies of seed and feed. Good infrastructure (roads and waterways), credit
systems and processing factories are also advantageous. Pangasius hypophthalmus (Tra
fish) is an omnivore that will feed on rice bran, broken rice and corn, cassava flour, trash
fish, fish-meal and vegetables in culture systems.
In Vietnam, rice bran usually contributes two thirds of the diet during grow -out of
Pangasius hypophthalmus (Tra fish). Homemade feeds normally consist mainly of rice
bran, broken rice, trash fish and vegetables. In Vietnam, cage feeds are prepared, mixed
and cooked at site, with the feed being presented as wet sticky balls. Fingerlings obtained
from the nursing ponds are grown in small cages to advanced fingerlings of 100 g and
these are stocked into grow -out cages. Culture is concentrated in Hong Ngu and Tan Hong
districts of Dong Thap province, though there has been a more recent spread to other areas,
including Thanh Binh, Cao Lanh, and Sa Dec town of Dong Thap province but the most
concentrated in An Giang province (Table 2.2).
Table 2.2 Status of Pangasius hypophthalmus pond culture in An Giang province
Year
Fish ponds and pits (ha)
Fish in rice field (ha)
Pen culture (ha)

Fish cages under rafts (pieces)

1995

2000

2001

2002

2003

2004

1,118.00

1,079.74

921.45

1,414.53

1,055.70

1,167.02

255

130

62

50

45

17

-

-

-

22

33

3,086

3,237

4,053

3,178

3,504

2,126

Statistic yearbook An Giang province (2004)

In modern floating cage culture, cages are placed and maintained in natural water
bodies and consist of wood or steel frames with nylon mesh (near Ho Chi Minh City) or
inox screens, and are attached to drums for floatation (Edwards, 2004; Pers. Comm.,
Philippe Cacot, CIRAD, 2005) but river cages culture in An Giang and Dong Thap
province constructed only by good quality wood, inox screens and steel but more
expensive for constructed. Cages in the Mekong River Delta range from 50 to 1600 m3 in
size, and larger cages commonly include living quarters for workers on the surface above
the submerged cages (Phillips 2002; Pers. Comm., Philippe Cacot, CIRAD, 2005).
At one time, Pangasius gigas (Basa fish) was the predominant species cultured
using cages (Trong, 2002), while Pangasius hypophthalmus (Tra fish) dominated total
aquaculture production (cage and pond aquaculture). Currently, the culture of Pangasius
hypophthalmus using cages has increased to surpass cage culture of Pangasius gigas (Basa
fish) (Pers. Comm, Philippe Cacot, 2005).
2.5.3

Pen Culture

Pen culture, like other methods of rearing fish, may be conveniently classified as
extensive, semi-intensive or intensive on basis of feeding and fish density. Extensive
culture relies solely on naturally available food such as plankton, detritus, benthos and drift,
10


and no supplementary feeding is given. Semi-intensive culture involves the addition of low
protein <10% of feedstuffs, usually compounded from locally available plants or
agriculture by products to supplement the intake of natural food, whereas in intensive
culture operations, fish rely almost exclusively on an external supply of high protein >20%
of food, usually based on fish meal. Recently, it has been reported that Pangasius

hypophthalmus (Tra fish) culture of wild-caught animals within barriers constructed in
(bamboo, wood, and nylon nets) occurs in An Giang province of Viet Nam. Pen size from
100m2 to 1,000m2; Stocking density and size: 40 fish/m2; 20g/fish; 40% water
exchange/day; Harvest size 1.1 kg/fish;
Discussion of NAGA, World Fish Center Newsletter carried out if technology for
culture in pens is improved in terms of pen materials, fabrication, stocking rate, feed and
feeding schedule, harvesting methods, etc., it may serve as a cheaper alternative to the
expensive land-based nurseries for raising advanced fingerlings for stocking the large
rivers and canal in Vietnam.
The most of systems intensive Pangasius hypophthalmus pens culture are
distributed in An Giang province and the area of water surface for pens culture and Veo
culture (hapas net) for this species in 2003 are 2,180 and rose 3,284 in 2004 (2004
statistical yearbook of An Giang province), maybe the areas of water surface for pens
culture and Veo (hapa net) culture will be increased in 2006 and following years and
continue develop in the future because this system provide many benefic for many farmers
of An Giang province and Mekong Delta of Vietnam.
2.6

Production statistics

Much of the finfish produced in Southeast Asia is consumed locally, although there
is a large export market. Pangasius hypophthalmus (Tra fish) is the predominant species
reared for export, while Pangasius gigas (Basa fish), considered a superior product, is, for
the most part, consumed domestically (Pers. Comm., Philippe Cacot, 2005). In 2003,
production of Pangasius gigas (Basa fish) was estimated to be between 10,000 and 50,000
tons and production of Pangasius hypophthalmus (Tra fish) was estimated to be greater
than 100,000 tons, with production steadily increasing. The government of Viet Nam
hopes to increase production of Pangasius gigas (Basa fish) to 50,000– 100,000 tons by
2010 while maintaining the production of Pangasius hypophthalmus at its current rate
(Edwards et al. 2004). In Viet Nam, in 2004, production of river catfish for the export

market alone reached 350,000 tons, 90% of which was Pangasius hypophthalmus (Tra
fish) (Pers. Comm., Philippe Cacot, 2005). Total production of pangasius for the export
market in July, 2006 (Figure 2.4)

11


Figure 2.4 Annual production of Pangasius spp for export in the Mekong Delta, Vietnam
2.7

Feeds and Feeding

Feed use in Pangasius hypophthalmus aquaculture is widely varied throughout the
four countries that produce the majority of farmed Pangasius hypophthalmus (Tra fish) and
Pangasius gigas (Basa fish) (Vietnam, Thailand, Lao PDR, and Cambodia). Much of the
information available on feed use in aquaculture operations in these countries is regionspecific. Additionally, since half of the feed used in river Pangasius spp pond, floating
cage and pen culture aquaculture are homemade; there is limited uniformity in feed use in
aquaculture operations. Feed and feeding used for Pangasius spp floating cage and pen
culture in An Giang Province for many years ago such as Pangasius waste feed,
Manufactured pelleted feed and wet homemade feed but farm made wet-feed is widely
used for example, mix 40% rice bran + 10% soybean meal + 50% fish meal FCR: 1.8 – 2.0
(Amara, 2006). Feeding rate: the firth of Month: 8 – 10% body weight, the second of
month: 6 – 7% body weight, the third of month: 4 – 5% body weight, the fourth of month:
3% body weight and from 5 to 7 months: 1.5% body weight (Amara, 2006) but now they
reused Pangasius waste after processing for feeding in floating cage and pen culture.
Until recently, in Vietnamese river Pangasius hypophthalmus (Tra fish) and
Pangasius gigas (Basa fish) floating cage and pen culture systems, 95 to 97% of floating
cage and pen used homemade feed (Phu & Hein, 2003. Lecturer of Can Tho University).
Current estimates indicate, however, that 50% of Pangasius hypophthalmus (Tra fish) and
Pangasius gigas (Basa fish) cages use wet homemade feed and 50% use manufactured

feed (Pers. Comm., Philippe Cacot, 2005). Small-scale farmers use an integrated
fisheries/aquaculture system that uses low-value fish species (trash fish), taken from
marine or freshwater systems (Edwards, 2004) either through by catch or targeted fisheries,
for aquaculture feed. Wet homemade feeds vary widely in their ingredients and nutritional
value (Edwards, 2004), and can have low and occasionally imbalanced nutritional value,
which results in low yield of marketable fishes; high fat accumulation in fish abdomens
due to these low nutritional feeds reduces the proportion of fillet meat in the final,
processed fish (Phu & Hein, 2003. Lecturer of Can Tho University). Manufactured pellet
feed is significantly higher cost than wet homemade feed, as manufactured feeds use
imported fishmeal and soybean cake (primarily from the U.S.), instead of the local sources
of “trash fish,” which are thought to be of low quality (Edwards, 2004; Pers. Comm.,
Philippe Cacot, 2005). Materials for making homemade feeds, on the other hand, are
locally available and cheap. The price of wet homemade feed is about US$0.12 – $0.13 per

12


kilogram (kg) of feed, and the price for manufactured pelleted feed is around US$0.27 –
$0.30 per kg of feed. Hence the feed cost for producing one kilogram of fish can range
from US$0.31 – $0.39 for homemade feed and US$0.38 – $0.45 for manufactured pelleted
feed (Phu & Hein, 2003. Lecturer of Can Tho University). However, these values will vary
greatly depending on the feed conversion ratio (FCR), which will be affected both by
protein content and rearing structure in the aquaculture operation. The recent of decline in
the use of wet homemade feeds has, in part, been due to the establishment of a feed
industry, increased large-scale production of Pangasius hypophthalmus (Tra fish), and a
shortage of trash fish, as well as the relationship between trash fish and pathogens such as
Vibrio spp. (Pers. C and Philippe, 2005).
Due to the low-tech nature of river catfish farms, feeding may not operate at its
most efficient, especially considering the common use of wet homemade aquaculture feeds.
Feeds vary in protein content and moisture content, and homemade feeds especially vary in

the type of trash fish and the amount of trash fish used in the feed (Pers. Comm., Kwei Lin,
ret. Asian Institute of Technology, April 13, 2005). FCRs vary accordingly with each
variation within the different types of feeds. Homemade feeds, with unknown moisture
content, typically result in the highest FCRs of any type of feed. Subsequently, FCRs are
typically lower for homemade feeds supplemented by manufactured feeds, depending on
cost, and even lower for manufactured pelleted feeds. Other studies have calculated an
average FCR for all Pangasius catfish, under all feeding regimes, of 2.5 (Table 2.3,
Edwards et al. 2004).
Table 2.3 Aquaculture using trash fish (Edwards, 2004)
Production
(mt)
180,000

(%) using
trash fish
80%

160,000

Marine fishes (grouper)
Loster (P.ornatus)

Species
Pangasius catfish
Shrimp(Penaeus monodon)

Trash fish (t)
Min
Max
64,800

180,000

2.5

Moist/wet
feed (t)
360,000

38%

4.75

287,280

71820

143,640

2,000

100%

5.9

11,800

11,800

11,800

1,000

100%

28

28,000

176,420

363,440

687,080

176,420

363,440

Total

FCR

Phu and Hein, indicate FCRs for homemade feeds range from 2.7 to 3.0 and FCRs
for manufactured pelleted feeds range from 1.4 to 1.5. FCRs also vary with stocking
densities and water quality associated with the rearing structure of the aquaculture
operation. In experiments done on aquaculture feed, Hung (2001) calculated FCR under a
number of conditions for both basa and Pangasius hypophthalmus (Tra fish). FCRs for
Pangasius hypophthalmus (Tra fish) ranged from 1.34 – 1.82, with higher values for day
feeding than for night feeding, while FCRs for Pangasius gigas (Basa fish) had a much
larger range, from 1.21 – 2.19, with the highest FCR values occurring with 1, 2, or 3

feedings during the day.

13


2.8

Nutritional requirements of Pangasius hypophthalmus

2.8.1

Protein and amino acid of fish

Total protein (amino acid balanced) requirements for optimum growth of catfish
Pangasius hypophthalmus have reported to range from 20% to 30% (Aizam et al., 1983
cited in Alawi, 1989). A minimum level of 25% protein is needed in the diet for optimum
growth of catfish Pangasius hypophthalmus fry in laboratory or intensive culture
(Chuapoehuk and Pothisoog, 1985). The main reasons for such a range are differences in
fish size, daily allowance, and amount of non-protein energy in the diet. Small catfish
increased in weight more rapidly when the dietary protein level was increased from 25% to
35% than did larger fish (Page and Andrews, 1973 cited in Lovell, 1989).
Catfish require essential amino acids (EAA) such as Arginine, Histidine, Isoleucine,
Leucine, Lysine, Methionine, Cystine, Phenylalanine, Tyrosine, and Valine. Cystine can
replace or spare about 60% of methionine on a molar sulfur basis. Tryosine can spare about
50% of the total phenylalanine requirement for channel catfish. Lysine and methionine
plus cystine appear to be first limiting amino acids, followed by lysine (National Research
Council, 1983).
2.8.2

Lipid requirement of fish

Lipid requirement of fish varies according to species, sex, and temperature, total
energy of feed, lipid type and digestibility. In general, optimal dietary lipid level in feed is
around 10-20%. At these dietary lipid levels, a high efficiency of protein utilization occurs
in fish and has a slight effect on carcass quality, with more than 20% causing increased
lipid deposition (Cowey and Sargent, 1979). Generally, if fish are fed with inadequate
dietary lipid, storage protein and carbohydrate (glycogen) are used for producing energy
supply and growth rate is standard. When fish are fed with excess dietary lipid, fat
deposition occurs (Henderason and Sargent, 1985).
The use of lipids (fats and oils) in catfish feeds is desirable because lipids are a
highly digestible source of concentrated energy, supply essential fatty acids, serve as a
vehicle for absorption of fat-soluble vitamins, increase feed palatability, and serve as
precursors for steroid hormones and other compounds. In the storage form, lipids affect the
flavor of fish and help maintain neutral buoyancy. The type and amount of lipid used in
catfish diets are based on essential fatty acid requirements, economic, and quality of fish
desired.
Essential fatty acids (EFAs) are fatty acids that cannot be synthesized in the
animal’s body; thus; they must be provided preformed in the diet. EFA requirements for
catfish and most other warm water fish have not been precisely defined, but it appears that
catfish require a small amount (about 0.50% - 0.75%) of n 3 fatty acids. This level can be
supplied by fish oil. Natural pond food organisms may also be a source of EFA. Generally,
lipid levels in catfish feeds are kept below 6% (Tucker, 1985).
2.8.3

Carbohydrate requirement of fish

Carbohydrates are compounds of carbon, hydrogen, and oxygen that include sugars,
starch, cellulose, gums, and other closely related compounds. Carbohydrates serve as the

14

least expensive source of dietary energy and aid in the pelleting quality of practical catfish
feeds. Therefore, some form of digestible carbohydrate should be included in fish diets
(Garling and Wilson, 1977 cited in Tucker, 1985).
Carbohydrate may also serve as precursor for various metabolic intermediates
necessary for growth. Thus, in the absence of adequate dietary carbohydrates or lipids, fish
will utilize dietary protein to meet their energy needs. When adequate energy is available
from either carbohydrate or lipids, much less protein will be used for energy and most will
be used for growth (Tucker, 1985).
2.8.4

Minerals requirement of fish

Fish require the same minerals as warm-blooded animals for tissue formation and
various metabolic processes. In addition, fish utilize inorganic elements to maintain
osmotic balance between fluids in their body and the water. Minerals in the water can
make significant contributions to the fish’s requirements for some minerals. Most fish can
absorb a major part of their calcium requirement from the water, across the gills, except
when the water is unusually low in dissolved calcium (National Research Council, 1983).
A dietary source of phosphorus is essential for fish because levels of dissolved phosphorus
are very low in natural waters in relation to calcium. Dietary deficiencies in phosphorus
have caused reductions in growth rate, appetite, and body content of calcium and
phosphorus in channel catfish (Lovell, 1984). Minimum requirement for available
phosphorus in diets for rapidly growing channel catfish is approximately 0.45%, whereas
dietary calcium is usually not considered in feed formulation (Lovell, 1989).
Natural feedstuffs are usually adequate in potassium, magnesium, sodium and
chlorine for normal growth of animals unless there is a high rate of mineral loss. These
elements are probably available in sufficient quantity in practical fish feeds without
mineral supplementation. However, fish feeds low in animal products may be deficient in

trace minerals, so a trace minerals mixture containing zinc, iron, copper, manganese, iodine
and selenium should be added to diets containing largely plant ingredients. A premix to
provide the requirements of zinc, iron, manganese, iodine, copper, and selenium are
recommended in commercial feeds.
2.9

Environment impacts

2.9.1

Effluent effects

While both of ponds, floating cages and pens aquaculture systems are used for
Pangasius gigas (Basa fish) and Pangasius hypophthalmus (Tra fish), cage aquaculture is
the more technologically advanced method, thus it is utilized more for the export market.
The cages utilized are essentially open net pens placed within the Mekong River Delta, so
effluent from the aquaculture operations is not treated before flowing out of the cages into
the surrounding environment.
There is concern regarding pollution from cage and pen effluent, as well as
regarding deterioration of water quality and an increase in observed fish disease outbreaks
(Phillips, 2002). Combined with high water temperatures, ammonia, nitrates, and organic
matter released in fecal wastes lead to rapid growth of algae and aquatic plants, and can
result in severe algal blooms and eutrophication of water bodies. Low levels of dissolved

15


oxygen in natural water bodies resulting from the decomposition of plants and other
organic matter could have affects on local fisheries, water quality, and other local resources
(Pers. Comm., Philippe Cacot, 2005). The Vietnamese government also suggests that the

carrying capacity of the Mekong River is high if factories are prohibited from discharging
effluents into the river (Edwards, 2004), while others observe that the impact of fruit and
rice production contributes significantly more to environmental degradation than does
aquaculture (Pers. Comm, Philippe Cacot, 2005).
2.9.2

Habitat effects

The introduction of intensive floating cage or pen culture to a water body have been
established cage farming to a water body has an impact on the environment which can lead
to conflict, since waters resource are often, and increasingly so, under pressure from other
users and for a wide variety of purposes, floating cage and pen structures affect a water
body has also an impact on the environment which have three principal ways: they take up
space, thus potentially competing with other users such as they after flow regimes which
govern the transport of oxygen, sediment, plankton and fish larvae; they have impact on
the aesthetic qualities of the site.
The purposes of study are to investigate the cage culture system and its related
environmental conditions, (a) to determine the quality and quantity of pollutants produced
by cages and pen, (b) to detect the fate of pollutants in the river, and to recommend
methods for pollution mitigation in cage culture because of the environmental impact of
fish cage or pen culture is an issue of increasing concern, since last two decade
(Beveridge,1984) but for cage and pen culture in Mekong River Delta and An Giang
province, Vietnam they have many research on some issue for environment impact
following:
Sitting and locations for cage production in Mekong River Delta is relatively
benign. The environment in this region is already highly degraded from non-aquaculture
sources, and the area is heavily used by a large human population. Additionally, large-scale
floating cage and pen aquaculture serves a dual purpose when combined with housing,
which is built above submerged aquaculture cages (Phillips, 2002).
In the Mekong River Delta, typical stocking densities of Pangasius gigas (Basa

fish) and Pangasius hypophthalmus (Tra fish) are 200 – 300 fish/m3 (Phillips, 2002) or 100
kg/m3 (Trong, 2002), which are considered intensive production levels. Despite intensive
production levels and the high pollution loadings, results from various studies show that
some 23% of C, 21% of N and 53% of P of feed input such as Pangasiusis waste,
homemade feed and pelleted into the cage culture system is being accumulated in the
bottom sediments and the significant impact is normally confined to within 1 km of the
farm. The major impact is on the bottom, where high sediment oxygen demand, anoxic
sediments, production of toxic gases and a decrease in benthic diversity may result.
Decreases in dissolved oxygen and increases in nutrient levels in the water are also evident
but are normally confined to the vicinity of the farm.
The presence of intensive floating cage and pen culture in both An Giang province
and Mekong Rivers in Vietnam has produced a heavy impact on the environment so based
on measured levels of carbon (C) phosphate (P) and Nitrogen (N) the trash feeds, excess
biomass and carrying capacity was compound. Excess trash fish and homemade fed to fish

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