optimisation of artemia biomass production in salt ponds in vietnam and use as feed ingredient in local aquaculture

Optimisation of Artemia biomass production in salt ponds in Vietnam and use as feed ingredient in local aquaculture Nguyen Thi Ngoc Anh... Nguyen Thi Ngoc Anh Optimisation of Artemia bi

Optimisation of Artemia biomass production in salt ponds in

Vietnam and use as feed ingredient in local aquaculture

Nguyen Thi Ngoc Anh

Faculty of Bioscience Engineering, Ghent University

Co-promoter: Dr Nguyen Van Hoa

College of Aquaculture & Fisheries, Can Tho University, Vietnam

Dean: Prof Dr ir Guido Van Huylenbroeck

Rector: Prof Dr Paul Van Cauwenberge

Examination Committee and Reading Committee (*):

Prof Dr ir Jacques Viaene (Chairman)

Department of Agricultural Economics, Faculty of Bioscience Engineering, Ghent University Jacques.Viaene@UGent.be

Prof Dr Peter Goethals (Secretary)

Department of Applied ecology and environmental biology, Faculty of Bioscience Engineering, Ghent University peter.goethals@ugent.be

Prof Dr Patrick Sorgeloos (Promoter), Department of Animal Production,

Faculty of Bioscience Engineering, Ghent University), patrick.sorgeloos@ugent.be

Prof Dr ir Peter Bossier (Department of Animal Production, Faculty of Bioscience

Engineering, Ghent University), peter.bossier@ugent.be

*Dr Nguyen Van Hoa (Co-promoter), College of Aquaculture & Fisheries, Can Tho

University, Vietnam nvhoa@ctu.edu.vn

*Prof dr Johan Mertens (Department of Biology, Faculty of Sciences, Ghent University)

johan.mertens@ugent.be

*Prof Dr Josse De Baerdemaeker (Laboratory of Agricultural Machinery & Processing,

Department of Agro-Engineering and Economics, Katholic University of Leuven) josse.debaerdemaeker@biw.kuleuven.be

*Dr Roeland Wouters (INVE Technologies, Belgium), r.wouters@inve.be

Nguyen Thi Ngoc Anh

Optimisation of Artemia biomass production in salt ponds in

Vietnam and use as feed ingredient in local aquaculture

Thesis submitted in fulfilment of the requirements for the degree of Doctor

(PhD) in Applied Biological Sciences

Optimalisatie van Artemia biomassa productie in zoutpannes in Vietnam and gebruik als

voeder-ingredient in lokale aquacultuur

To cite this work:

Anh, N.T.N (2009) Optimisation of Artemia biomass production in salt ponds in Vietnam

and use as feed ingredient in local aquaculture PhD thesis, Ghent University, Belgium

The author and the promoters give the authorisation to consult and to copy parts of this work for personal use only Every other use is subject to the copyright laws Permission to reproduce any material contained in this work should be obtained from the author

ISBN 978-90-5989-308-5

This study was funded by Vietnamese government, PhD scholarship of the Vietnamese Overseas Scholarship Program (322 project), and the CWO scholarship of the Faculty of Bioscience Engineering, Ghent University, Belgium

First of all, I would like to express my deep gratitude to my promoter, Prof dr Patrick Sorgeloos for giving me the opportunity to study at Ghent University His scientific orientation, encouragement, and support during my four year study, especially his patience

in correcting the papers and final thesis drafts during his already busy time

Special thank to my co-promoter Dr Nguyen Van Hoa (Can Tho University, Vietnam) for

his scientific guidance, encouragement and experience on Artemia research

My sincere thanks go to my supervisors Dr Gilbert Van Stappen and Mathieu Wille for their devoted and thoughtful revision and recommendations in the preparation and completion of all chapters of the thesis

I sincerely thank Prof Dr Josse De Baerdemaeker (Catholic University of Leuven, Belgium), Nguyen Thuan Nhi (College of Technology, Can Tho University) for giving me the basic knowledge and critical suggestions in the design of the experimental solar drier, and Dr Vu Quang Thanh for instruction in indoor drying techniques and allowing me to utilize the drying machines and equipment, and Phan Thanh Dung for his help during the drying experiment in the College of Technology, Can Tho University

I am grateful to Prof Dr Truong Quoc Phu, Dr Tran Thi Thanh Hien, Dr Vu Ngoc Ut and Duong Thuy Yen (College of Aquaculture and Fisheries, Can Tho University) for their proper suggestions on experimental designs, feed formulation and for providing me with facilities and space to perform the feeding trials

I am greatly indebted to Peter Baert for his valuable recommendations with data-processing

on the Artemia experiments and also willing to help me whenever needed

I am especially thankful to the members of the examination and reading committee, Prof

Dr ir Jacques Viaene; Prof Dr Patrick Sorgeloos, Prof Dr ir Peter Bossier, Prof Dr Johan Mertens, Prof Dr Peter Goethals (Ghent University), Prof Dr Josse De Baerdemaeker (Catholic University of Leuven), Dr Nguyen Van Hoa (Can Tho University) and Dr Roeland Wouters (INVE Technologies NV, Belgium) for their critical reviews and extremely valuable suggestions to improve this thesis

My warmest thanks go to Magda Vanhooren, who kindly helped me whenever needed

I am greatly indebted to Geert Van de Wiele and Anita De Haese for HUFA and proximate

composition analyses of the Artemia samples

I deeply thank the staff of ARC: Dorina Tack, Alex Pieters, Marc Verschraeghen, Jean

Dhont, Bart Van Delsen, Kristof Dierckens, Marijke Van Speybroeck, Christ Mahieu,

Special acknowledgements are due to Prof Dr Nguyen Anh Tuan, the rector of Can Tho University and Prof Dr Nguyen Thanh Phuong, the dean of the College of Aquaculture & Fisheries, for allowing me to study abroad

Many thanks to Dr Duong Nhut Long, Dr Nguyen Van Kiem, Dr Tran Ngoc Hai and Dr Ngo Thi Thu Thao from the College of Aquaculture & Fisheries for their support and providing me enough free time to accomplish this thesis

I owe special thanks to my colleagues Huynh Thanh Toi for his endless kindness and all his help in Ghent and in Vietnam, Nguyen Thi Hong Van for her provision of scientific journals, encouragement and supporting experimental equipment, Tran Huu Le and Le Van

Thong for helping me with filtering chlorophyll a samples, transporting water samples to

Can Tho for analysis and biomass collection

I greatly appreciate Le Van Nhieu, Phan Thanh Phuoc, Giang Van Nghiep, Giang Van Hay, Nguyen Duyen Hai, Nguyen Thi Phuong, Tran Thi Yen who have been devoted hard workers in Bac Lieu salt works and for their enthusiasm and efficient support during my field study in Vinh Hau station, Bac Lieu province

Many thanks to my PhD colleagues: El-Magsodi Mohamed, Natrah Ikhsan, Kartik Sri Barua, Gunasekara Asanka, Dang To Van Cam, Le Hong Phuoc, Dinh The Nhan, Nguyen Duy Hoa, Nhu Van Can, Ho Manh Tuan and others for their encouragement and support during my study in Ghent

To all Vietnamese students in Ghent, I thank you for your moral support during my stays in Ghent I would like to express my warmest feelings to all my friends and my colleagues in various institutions and universities, Can Tho University and College of Aquaculture and Fisheries, who always were concerned about my PhD completion

I am very grateful to the Ministry of Education & Training, Vietnamese Government for providing me with a scholarship to pursue my PhD study and the Faculty of Bioscience Engineering, Ghent University, Belgium through the CWO scholarship for the defence of this thesis

My great gratefulness goes to my grandmother, my aunts, my brothers and sisters who always encouraged me to finish my PhD, especially my mother who always gave me all physical and moral support, but unfortunately does not live anymore

I wish to dedicate this thesis to my husband Phan Huu Tam, who has sacrificed a lot during

my four years intensive study This thesis is a present for him

Chapter 1 General introduction 1

Chapter 2 Literature review 7

Chapter 3 Culture of Artemia biomass Section I Effect of partial harvesting strategies on Artemia biomass production in salt works 31

Section II Effect of different food supplements on proximate compositions and Artemia biomass production in salt works 47

Secttion III Effect of different ratios of N:P on primary productivity: its combination with feeding strategies for Artemia biomass production in salt ponds 69

Chapter 4 Drying Artemia biomass Section I Total lipid and fatty acid contents of Artemia biomass dried using different drying techniques 109

Section II Effect of solar drying on lipid and fatty acid composition of dried Artemia biomass 117

Chapter 5 Application of Artemia biomass for target aquaculture species Section I Formulated feeds containing fresh or dried Artemia biomass as live food supplement for larval rearing of black tiger shrimp, Penaeus monodon 151 Section II Effect of fishmeal replacement with Artemia biomass as protein source in practical diets for the giant freshwater prawn Macrobrachium rosenbergii 141

Section III Effect of different forms of Artemia biomass as a food source on survival, molting and growth rate of mud crab, Scylla paramamosain 157

Section IV Substituting fishmeal with Artemia meal in diets for goby Pseudapocryptes elongatus: effects on survival, growth and feed utilization 173

Chapter 6 General discussion and conclusions 207

Chapter 7 References 216

Summary/Samenvatting 239

Curriculum vitae 247

Σ Total

°C Degree Cencius

ANOVA Analysis of variance

AOAC Association of Official Analytical Chemists APHA American Public Health Association

ARA Arachidonic acid

DHA Docosahexaenoic acid

DIN Dissolved inorganic nitrogen

DRP Dissolved reactive phosphorus

DW Dry weight

EFA Essential fatty acid

EPA Eicosapentaenoic acid

FA Fresh/frozen Artemia

FAME Fatty acid methyl easters

FAO Food and agriculture organization

FFA Free fatty acid

min Minute

MKD Mekong delta

ml Milliliter

mm Millimeter

MoFI Ministry of Fisheries

MUFA Mono-unsaturated fatty acid

CHAPTER

General introduction and thesis outline

General introduction

Populations of the brine shrimp Artemia (Crustacea, Anostraca) are typical inhabitants of

extreme environments, such as hypersaline inland lakes, coastal lagoons, and solar salt works, distributed all over the world, and characterized by communities with low species

diversity and simple trophic structures (Lenz, 1987; Lenz and Browne, 1991) Artemia can

be found in a great variety of habitats in terms of water chemistry (Lenz, 1987; Bowen et

al., 1988), altitude (Triantaphyllidis et al., 1998; Van Stappen, 2002) and climatic conditions, from humid-subhumid to arid areas (Vanhaecke et al., 1987)

The first use of Artemia nauplii, hatched from cysts, is known from the 1930s when this

zooplankton organism was used as a suitable food source for fish larvae in the culture of

commercially important species (Sorgeloos, 1980b; Léger et al., 1986) Since then, Artemia

has been found to be a suitable food for diverse groups of organisms of the animal kingdom, especially for a wide variety of marine and freshwater crustaceans and fishes

(Sorgeloos, 1980b) Also decapsulated Artemia cysts, juvenile and adult Artemia have

increasingly been used as appropriate diets for different fish and crustacean species (Sorgeloos et al., 1998; Dhont and Sorgeloos, 2002; Lim et al., 2003)

Since the early 1990s cyst consumption has increased exponentially as a consequence of the

rapidly expanding shrimp and marine fish industries (Sorgeloos et al., 2001; Dhont and Van Stappen, 2003) On the other hand, the limited supply of Artemia cysts, originating from

natural harvests, may lead to a serious bottleneck in many aquaculture developments (Lavens and Sorgeloos, 2000b) In particular, in South East Asia where no natural

populations of Artemia occur, therefore diversification of Artemia sources has been

considered a possible solution to sustain the fast growing aquaculture industry This

strategy has been performed by the exploration of natural harvesting from new Artemia

sites such as China (Xin et al., 1994), Iran (Van Stappen et al., 2001), Mexico and Chile

(Castro et al., 2006) etc Furthermore, man-made introduction of Artemia into saltworks

and man-made ponds has also contributed to supplement cyst supply This approach has been conducted during the last couples of decades in several countries with a monsoon

climate For instance, Philippines (De Los Santos et al., 1980), Thailand (Tarnchalanukit and Wongrat, 1987), Vietnam (Quynh and Lam, 1987; Brands et al., 1995) and other

countries such as India, Sri Lanka, Iran (Hoa et al., 2007)

In Vietnam, Artemia production is successfully conducted on a seasonal basis in the

coastal areas of the Mekong Delta, southern Vietnam (Brands et al., 1995; Baert et al.,

1997) To date this region is an important supplier of high-quality Artemia cysts that are

used in domestic aquaculture as well as for export This activity has had significant positive socio-economic impacts for the local rural populations (Hoa et al., 2007; Son, 2008) In practice, cysts produced during the previous culture season are used to establish, by

inoculation, a new population of Artemia This practice may favour the accumulation of adaptations to the new environment (Frankenberg et al., 2000) This Artemia culture system

is referred to as semi-intensive (Tackaert and Sorgeloos, 1991) and static (Quynh and Lam, 1987; Brands et al., 1995) Semi-intensive refers to small seasonal man-managed ponds in

which Artemia is inoculated at high densities (between 60 and 100 nauplii L-1) Ponds are managed intensively (i.e inoculation of selected strains, manipulation of primary and secondary production, predator control, etc.) but most of the management procedures are

empirical Furthermore, Artemia production in Vietnam has largely focused on cyst production, and all techniques and methodologies developed to optimize Artemia

production have used maximal high-quality cyst production as their primary target (Brands

et al., 1995; Baert et al., 1997; Hoa et al., 2007)

Artemia is a non-selective particle feeder, feeding on microalgae, detritus and bacteria,

where the only limiting factor is the size of the ingested particles (Van Stappen, 1996; Fernández, 2001; Dhont and Sorgeloos, 2002) Although the feeding and filtration biology

of Artemia has been studied in laboratory tests (Coutteau and Sorgeloos, 1989; Evjemo and

Olsen, 1999; Fernández, 2001), up to now, this type of study has not been extended to the

field, and there is very little information on optimal Artemia biomass production in salt works Artemia biomass is an excellent food source in aquaculture as it converts detritus

and phytoplankton into high-quality proteins, thus extracting nutrients from the aquatic

environment (Sorgeloos, 1985) Artemia biomass is valorised as a high-quality feed for

ornamental fish (Lim et al., 2001; 2003), as a nursery food for marine fish, shrimp, prawn and crab (Merchie, 1996; Sorgeloos et al., 1998; Dhont and Sorgeloos, 2002), as an overall high-protein ingredient for aquaculture feeds, and as maturation trigger in shrimp broodstock (Naessens et al., 1997; Wouters et al., 2002)

In pond systems, the success of Artemia cyst and biomass production relies on the favourable growth of the Artemia population after inoculation This growth is, amongst

others, significantly influenced by the food management of the culture ponds The final

yield of Artemia biomass can also be considerably affected by various technical aspects,

such as harvesting strategies (Brands et al., 1995; Baert et al., 1996, Anh and Hoa, 2004) Hence, substantial research is required to (1) optimize culture techniques, in particular in relation to the effects of organic and inorganic fertilizers on the production of microalgae as

a natural food for Artemia, (2) on the use of supplementary feeds and (3) on adequate

harvesting strategies Moreover, there is a need for (4) research into the possible

applications of Artemia biomass products in Vietnamese aquaculture Farming of highly

valuable aquaculture species in the Mekong delta has been studied for several species such

as Penaeid shrimp (Nghia et al., 1997a,b; Phuong et al., 2008), freshwater prawn

Macrobrachium rosenbergii (Thang, 1995; Lan et al., 2006) Similar work exists for the

mud crab Scylla spp (Dat, 1999; Ut et al., 2007a,b) and for different types of polyculture of marine and freshwater species (Rothuis et al., 1998; Minh et al., 2001; Lan et al., 2003)

Recently, Vietnamese aquaculture activities have been expanding with the culture of new target marine aquatic species such as swimming crab (Portunidae), cobia (Rachycentridae), grouper (Serranidae), goby (Gobiidae), eel (Anguillidae), Areola babylon (Buccinidae), etc (MoFI, 2006) These new species offer opportunities for diversification in the use of

Artemia, including live juveniles and adults as well as frozen or dried Artemia biomass

This indicates that there is a high potential market for Artemia biomass not only in the Mekong Delta but also along the coast line of central Vietnam (Hoa et al., 2007)

Research objectives

The general objectives of this thesis are firstly to improve Artemia pond management in

terms of the supply of natural and supplementary foods, and by adaptation of biomass harvesting strategies It also aims to develop a simple and cheap processing technique for

Artemia biomass, resulting in a product which is suitable for application in local

aquaculture operations in the Mekong Delta

The specific objectives and the thesis outline are as follows:

Chapter 1 (General introduction and thesis outline) describes an outline covering the

main topics of this thesis

Chapter 2 (Literature study) presents the biology and ecology of Artemia, and gives an

overview of aquaculture as well as the history of Artemia study in Vietnam It comprises

general geographic and climatological information on the site where the field research has

been conducted It describes the general principles of Artemia biomass pond production in

this area, and its various applications in local aquaculture It also provides a summary of

drying methods currently used in food and feed processing technology

Chapter 3 (Culture of Artemia biomass) describes the experimental work aiming to

optimize Artemia biomass production in salt ponds This chapter consists of three parts:

- Effect of partial harvesting strategies on Artemia biomass production in salt works

(Section I)

- Effect of different food supplements on proximate compositions and Artemia biomass

production in salt works (Section II)

- Effect of different ratios of N:P on primary productivity: its combination with feeding

strategies for Artemia biomass production in salt ponds (Section III)

Chapter 4 (Drying Artemia biomass) describes tests aiming to work out a simple and

cheap drying method for Artemia biomass, resulting in a product with appropriate quality

for use in aquafeeds It comprises two parts:

- Total lipid and fatty acid contents of Artemia biomass dried using different drying

techniques (Section I)

- Effect of solar drying on lipid and fatty acid composition of dried Artemia biomass

(Section II)

Chapter 5 (Application of Artemia biomass for some target aquaculture species)

evaluates the potential uses of different Artemia biomass preparations as feeds in the

larviculture and nursery phases of the important cultured species in the Mekong delta It contains four parts

- Formulated feeds containing fresh or dried Artemia biomass as live food supplement for

larval rearing of black tiger shrimp, Penaeus monodon (Section I)

- Effect of fishmeal replacement with Artemia biomass as protein source in practical diets

for the giant freshwater prawn Macrobrachium rosenbergii (Section II)

- Effect of different forms of Artemia biomass as a food source on survival, molting and

growth rate of mud crab Scylla paramamosain (Section III)

- Substituting fishmeal with Artemia meal in diets for goby Pseudapocryptes elongatus:

effects on survival, growth and feed utilization (Section IV)

Chapter 6 (General discussion) restates and discusses the overall results of the

experiments conducted in this thesis Based on the discussion, the general conclusions are drawn and prospective research topics are proposed

Chapter 7 (References) contains all the bibliographic citations mentioned in this thesis

CHAPTER

Literature study

Literature study

1 Overview of aquaculture in Vietnam

Globally, aquaculture is the fastest growing food-producing sector, with a total production

of almost 63 million metric tonnes in 2005, more than five times the amount produced in

1985 Asian countries play an important role in the development of the aquaculture sector, accounting for more than 90% of global aquaculture production Three quarters of global aquaculture production is generated from Asian countries, with China and Vietnam ranking

as the first and third global producers Among the top ten Asian producers, Vietnam experienced the fastest growth between 1985 and 2005, which has raised concerns among several stakeholders concerning the sustainability of the aquaculture sector in Vietnam (Corsin, 2007)

Vietnam has great potential for aquaculture development including marine, brackish and fresh waters, all of which are widely available throughout much of the country There are 3,260 km of coastline, 12 lagoons, straits and bays, 112 estuaries, canals and thousands of big and small islands scattered along the coast On the land, an interlacing network of rivers, canals, irrigation and hydroelectric reservoirs has created a great potential of water surface with an area of about 1.7 million ha (Final report of Ministry of Fisheries (MoFI) and World Bank, 2005)

In 2006, the total area of water surface used for aquaculture in Vietnam was 1,050 thousand

ha, which represents a 64% increase over the 641.9 thousand ha used in 2000 A variety of species are cultivated in these waters, but shrimp and catfish are by far the most prevalent Total aquatic production increased almost 7% in 2006, while aquaculture production increased 14.6% (Huong and Quan, 2007) The rapid development of the aquaculture sector achieved during the last two decades has been a direct result of the sector diversifying its farming practices and adapting to the production of exportable species at increased levels of intensification In 2007 the total aquaculture area accounted for more than one thousand hectares and it was reported that the total aquaculture area and productivity have increased 2.1 and 2.5 times, respectively, compared to that in 1996 A similar tendency was also found in the Mekong Delta (MKD) in South Vietnam (Figure 1) In addition, the total output value of aquaculture in 2006 was 47,446.9 billion VNDs, which corresponds with a

4.03 times increase, compared with 11,761 billion VNDs in 2000 (General Statistics Office, 2008; www.gso.gov.vn/default/news)

Figure 1 Aquaculture culture area and productivity in Vietnam in general and in the

Mekong delta between 1996 and 2007 (Source: Data from General Statistics Office, Vietnam, 2008)

The Mekong Delta has an area of 3.9 million ha, accounting for 12% of the total area of Vietnam Agriculture occupies 83% of the total delta so it plays an important role in the development of the economy in Vietnam (Ni et al., 2003) In addition, this delta is the most important region in Vietnam for both fisheries and aquaculture, accounting for 43 and 67 %

of the nation’s total production, respectively, and for 57 % of the total export values in

2003 The Mekong Delta has also the most diversified aquaculture farming activities and has a large potential for increased aquaculture production (MoFI, 2005) The culture

systems include pond, fence and cage culture of catfish (Pangasius) as well as several indigenous species such as snakehead fish (Channa), climbing perch (Anabas) and giant freshwater prawn (Macrobrachium) Moreover, integrated farming systems such as rice-

cum-fish, rice-cum-prawn and mangrove-cum-aquaculture are broadly practiced across this region (Minh et al., 2001; MoFI, 2006) Particularly, the Vietnamese Government has promulgated a long term planning to develop sustainable aquaculture in the country, namely “Decision No 10/2006/QÐ-TTg dated Jan 11, 2006.” The objectives of this plan are the following: aquaculture production in 2010 will be about 2 million tonnes, including

0.98 million tonnes from fresh water aquaculture and 1.02 million tonnes of marine and brackish water aquaculture; 1.1-1.4 million ha of water bodies will be exploited for aquaculture activities, of which there are 0.6 million ha of freshwater area and 0.7 million

ha of brackish water and marine areas In parallel, applied research, education and training activities have been developed to meet the need for the sustainable and effective development of the fisheries sector, particularly in aquaculture during the period 2005-

2010

2 Trends in the use of fishmeal in Vietnam

Since aquaculture is developing rapidly in Vietnam, the future demand for fish meal (FM)

as an ingredient in aquafeeds is expected to increase dramatically FM availability in Vietnam is low and FM produced domestically is mostly of poor quality because of inadequate preservation of trash fish on board Consequently, Vietnam only uses domestically produced FM for livestock and some freshwater fish for grow-out feed as it is generally of low quality FM for higher quality feed for fish fingerlings and crustaceans is imported and represents about 90% of the total FM used Fish oil for aquafeed manufacture

is also imported (Edwards et al., 2004)

A prognosis made by MoFI (2006) shows that about 150,000-200,000 tonnes of FM will be required over the next decade for aquaculture, two to three times the present level of use However, the price of imported FM continues to rise and therefore the development of Vietnamese aquaculture will be influenced strongly by the price for FM and oil on the international market (Edwards et al., 2004) Moreover, Huong and Quan (2007) reported that the aquatic feed industry is scrambling to keep pace with increased demand for commercially made feed from the booming aquaculture industry in the Mekong Delta where the major aquaculture activities in Vietnam are located Latest available statistics indicate that Vietnam’s 39 industrial aquatic feed producers in 2001 had a production capacity of about 50,000 tonnes year-1 This would only satisfy about 40% of today’s aquaculture feed demand More and more the trend among farmers is to replace traditional home-made feed with industrial feed, hence the higher demand for industrial fish feed Feed cost may contribute to more than 50% of the total cost of an aquaculture operation Moreover, the MoFI target of 200,000 tons of marine fish by 2010 would in theory require

at least 2 million tonnes of trash fish based on current practices, which is unattainable without investments in more efficient feeds and feeding practices Consequently, due to the

need to reduce the dependence of the aquaculture industry upon a wild and finite food resource, feed manufacturers and researchers alike have spent considerable time and effort

in trying to find dietary replacements for FM and fish oil within compound aquafeeds This has contributed to a reduction in input costs for production (MoFI, 2005) The development

of alternative dietary protein and lipid sources as partial or total replacements of FM in the formulated aquafeeds, have been intensively studied and applied Different sources of materials can be used, especially cheap raw materials which are locally available, such as terrestrial animal by-products, fish offal from processing and agricultural by-products, (FAO, 2002)

3 Overview of main target aquaculture species

Some target aquaculture species in the Mekong delta with high economic values on the home and export markets are briefly described below:

Black tiger shrimp (Penaeus monodon)

Shrimp culture is considered as one of the most lucrative industries because of its high

market price and great demand on the international market The black tiger shrimp Penaeus

monodon is the most prominent farmed crustacean products in international trade, and has

driven a significant expansion in aquaculture in many developing countries in Asia Global

aquaculture production of P monodon increased gradually from 21,000 tonnes in 1981 to

(MoFI, 2005; 2006) Total culture area and productivity increased by 3.1 and 6.7 times respectively from 1999 to 2007, with an average annual increase of 35.3% (General Statistics Office, 2008) However, the rapid expansion of shrimp farming has brought about some problems such as lack of high quality shrimp postlarvae and knowledge of culture techniques Moreover, the existing irrigation systems do not meet the need for appropriate operation of shrimp farming As a result, the frequent occurrence of diseases is a major constraint to the sustainability in the culture regions (MoFI, 2006) To reduce this risk, alternative culture species and diversification of species have been taken into account

Recently, white shrimp Litopenaues vannamei has become the important cultured shrimp

species, the production of the white shrimp in Vietnam was 6,268 tons in 2005 (MoFI, 2006)

Mud crab (Scylla spp.)

Exploitation of the world’s mud crab resources has increased dramatically over the past 30

years and aquaculture of mud crab, Scylla spp., contributes largely to the world production

of the genus (FAO FIGIS database; www.fao.org/ES/ess/figis.asp) Moreover, mud crabs are large size animals with high nutritional value, and are of high commercial value in SoutheastAsian countries (Keenan, 1999)

In Vietnam, capture fisheries of mud crab is about 1400 tonnes annually and large part obtained from aquaculture and approximately 6,000 tonnes of crab was exported to China

in 2004, accounting for 25 millions US dollars (MoFI, 2005) Mud crab has been the first candidate as alternative to shrimp culture because it is the only species that has been cultured traditionally in the coastal area besides shrimp (Dat, 1999; Ut, 2003) The natural potential for mud crab culture development in Vietnam is great; with 858,000 ha of marine and brackish water area available for shrimp and mud crab culture (Lindner, 2005) Moreover, Thach (2007) reported that the total area of semi-intensive and intensive mud

crab culture has been estimated to be well in excess of 40,000 ha Mud crab Scylla

paramamosain is the most prevalent species used in aquaculture farms in the Mekong delta (MKD), and has become increasingly popular over the past decades (Nghia et al., 2001; Ut, 2003) In 1995, the culture area and production of crab in the Mekong delta were 3086 ha and 1644 tonnes (Tuan et al., 1996) whereas in 2004 they were estimated to be about 7,500

ha and over 7,000 tonnes (MoFI, 2005) Many farmers have indicated that their income from crab is more reliable than that from shrimp (Ut et al., 2007c)

The diverse culture systems used to farm crabs are similar to the range of methods used for shrimp aquaculture: polyculture systems in which two or more aquatic species are raised together are quite common in the Mekong delta: grow-out of crabs from juvenile to marketable size in open extensive mangrove forest-aquaculture-fishery farms or semi-intensive pond units; fattening of immature females to maturity; fattening of ‘thin’ crabs; and soft-shell crab production (Dat, 1999; Ut et al., 2007c) A 2005 survey of the eight eastern coastal provinces in the MKD indicated that crab productivity was highest (1,008

kg ha-1) in monoculture and lowest (75 kg ha-1) in mangrove-shrimp integrated culture (Ut

et al., 2007c) In the improved extensive systems of mud crab stocked at a density of 1 crab 5-10 m-2, yields are usually about 200-300 kg ha-1 crop-1 while in intensive aquaculture systems in which mud crab is stocked at 1-2 crab m-2 1.5-2.0 tonnes ha-1 crop-1 can be obtained, although yields of about 1 ton ha-1 are more common (Lindner, 2005; Thach, 2007) However, in previous years mud crab farming relied entirely on wild seed stock and the main obstacle for the development of mud crab culture is the availability of hatchery-reared seed (Keenan, 1999; Xuan, 2001; Ut, 2003)

Nowadays, mud crab reproductive technology has been improved remarkably; over 100 millions of mud crab seeds are produced from more than 150 mud crab hatcheries yearly The seeds are reared on 115,276 ha of land and produce about 480 tonnes of commercial mud crab per year Seed production techniques have been perfected and the supply is considered reliable Most crab aquaculture production now relies on commercial hatchery-reared stocks Therefore, expansion of mud crab aquaculture is realistic (Lindner, 2005; Thach, 2007) Nonetheless, hatchery-produced seed supplied to farmers is typically in the form of small postlarval crabs between 4 and 8 mm carapace width, resulting in low survival and productivity (Ut et al., 2007a) Thus a nursery period is a necessary intermediate step in crab production between hatchery and grow-out, to grow postlarvae to

a size appropriate for transport and release into large extensive to intensive production systems (Ut et al., 2007a; Rodriguez et al., 2007) Additionally, with respect to economic efficiency, utilizing locally available feeds for nursery of crab postlarvae to achieve high survival and good growth also play an important role as crabs are characterised by their high cannibalism

Goby (Pseudapocryptes elongatus)

The goby, Pseudapocryptes elongatus is a commercially important species for food in

Japan and Taiwan (Ip et al., 1990); It is also a highly valuable fish for domestic consumption as well as for exportation in Vietnam (Dinh et al., 2004), It is well adapted to

a wide range of environments so that recently it has become an important alternative species for integrated brackish water aquaculture (Dinh et al., 2004; Khanh, 2006) According to the Agriculture Statistics, the alternative goby-shrimp or goby-salt culture models have widely been applied in the coastal provinces of the Mekong delta such as Soc Trang, Ca Mau, Ben Tre and Tra Vinh This can help the farmers to improve their income and concurrently contribute to diminish the vulnerability of shrimp culture The production areas have increased noticeably from a few hectares in 2000 to 1,500 ha in 2008, in which Soc Trang and Bac Lieu made up 800 ha (www.vnn.vn/kinhte/2008/10/807666/) In extensive goby culture in salt works in the rainy season, the yield was 0.5-0.7 tonnes ha-1crop-1 and the income was 20-25 millions VND ha-1 (Bac Lieu Extension Service, 2007) Survey data also show that the semi-intensive and intensive culture of goby in shrimp ponds has been developing rapidly in the coastal provinces of the Mekong Delta in recent years: at stocking densities of 30-100 fish m-2, after 4-5 months of culture, productivity was

in the range of 3-6 tonnes ha-1 crop-1, and net income was between 50 and 100 millions VND ha-1 crop-1 (Nhon, 2008) Nevertheless, the constraint in goby culture is that the seed supply completely relies on the wild; the quality of fingerlings is usually unstable and their size is small causing high mortalities and low productivity (Khanh, 2006; Chung, 2007) Hence, nursery of goby using local available high quality feed to attain larger size fry with good quality for stocking in grow-out ponds is essential This approach could contribute to improve profitability for farmers and the development of the farming of this species

Giant freshwater prawn (Macrobrachium rosenbergii)

There has been a very rapid global expansion of freshwater prawn farming since 1995 The

total global production of Macrobrachium is estimated to reach 0.8 - 1.0 million tonnes

year-1 by the end of this decade; most of which is produced in Asia in which China is the leader, followed by Vietnam and India (New, 2005) Currently, the giant freshwater prawn

(Macrobrachium rosenbergii), which is indigenous to the Mekong river Delta, Vietnam, is

becoming an increasingly important target species for aquaculture (Phuong et al., 2006b)

The total culture area and production of M rosenbergii in the Mekong Delta were 4,759 ha

and 3,358 tonnes in 2003 (MoFI, 2005) and 9,077 ha and 9,514 tonnes in 2006 (Sinh, 2008) This species is cultured in ponds, pens and integrated or alternated with paddy rice production; alternate culture of rice with prawn is considered to have high potential to raise the income among impoverished farmers and to contribute to enhance rural development in Vietnam (Khanh and Phuong, 2005; Lan et al., 2008) The productivity of prawn culture varies with the culture practices employed and ranges from 100-887 kg ha-1 crop-1 for integrated rice-prawn culture systems, to 384-1,681 kg ha-1 crop-1 for alternate rice-prawn culture (Khanh and Phuong 2005), and 1,400-1,600 ha-1 year-1 for pen culture (Son et al., 2005)

Advantages of freshwater prawn farming in rice fields are lower stocking densities, lower investment and feed costs as well as absence of major diseases as associated with marine

shrimp farming (Phuong et al., 2006a) Besides, M rosenbergii prawn can grow well in

brackish waters having salinity up to 10 g L-1 (New, 2002; Cheng et al., 2003), thus prawn culture has been considered as an alternative to shrimp in low salinity areas and coastal

saline soils in order to reduce the threats of disease outbreaks in tiger shrimp, P monodon

Increase in prawn culture has led to a growing demand for postlarvae (PL) from hatcheries and most prawn farmers desire to stock PL with larger size to reduce mortality and shorten

the grow-out period Feed is the single largest cost item for M rosenbergii culture, as it

constitutes 40-60% of the operational costs (Phuong et al., 2003; Mitra et al., 2005) Hence, nursery of prawn PL using locally available protein sources as an ingredient in practical diets to improve cost-effectiveness with higher survival and better growth is necessary

4 Biology and ecology of Artemia

The genus of the brine shrimp Artemia consists of several bisexual species, identified by

reproductive isolation, and numerous parthenogenetic populations (Triantaphyllidis et al., 1998; Abatzopoulos et al., 2002) The systematic classification of the genus is as follows:

Artemia is a cosmopolitan organism, inhabiting coastal lagoons as well as inland salt lakes

where there are no or few predators and competitors In these hypersaline environments which are not tolerable by other filter feeders, brine shrimp survive thanks to their

physiological adaptations Artemia distribution is not continuous; the populations are found

throughout the tropical, subtropical and temperate climate zones (Persoone and Sorgeloos,

1980; Van Stappen, 1996) The geographical isolation of Artemia populations has led to

numerous geographical strains that have adapted to conditions that fluctuate widely with regard to temperature, salinity and ionic composition of the biotope (Bowen et al., 1985,

1988) Artemia can be found at altitudes from as low as sea level up to almost 4,500 meters

e.g Tibet (Abatzoupolos et al., 1998; Van Stappen, 2002) and in climatological conditions ranging from humid, sub-humid to arid regions (Vanhaecke et al., 1987)

Figure 2 summarizes the life cycle of Artemia The fertilized eggs in the brood pouch of the

female develop into either free-swimming nauplii (ovoviviparous reproduction) or, alternatively, when reaching the gastrula stage, they are surrounded by a thick shell and are

deposited as cysts, which are in diapause (oviparous reproduction) (Jumalon et al., 1981) Oviparity and ovoviviparity are found in all Artemia strains, switching of reproductive

mode in the natural environment can be expected to vary depending on the environmental conditions (Lenz, 1987) Other factors such as temperature, salinity, photoperiod and brood number also potentially contribute to a shift of mode of reproduction (Berthélémy-Okazaki and Hedgecock, 1987) Females can change in-between two reproduction cycles from oviparity to ovoviviparity or the other way round, but the entire progeny in a specific brood will be either cysts or nauplii The cysts usually float in the high salinity waters and are blown ashore where they accumulate and dry As a result of this dehydration process the diapause mechanism is generally inactivated; cysts are in a state of quiescence and can resume their further embryonic development when hydrated in optimal hatching conditions (Van Stappen, 1996)

The postembryonic development continues through about 15 molts in total, and the organism reaches the adult stage after about two weeks, depending on environmental conditions (Sorgeloos, 1980a; Clegg and Conte, 1980) Under optimal conditions brine shrimp can live for several months, grow from nauplius to adult in only 8 days time and reproduce at a rate of up to 300 nauplii or cysts every 4 days (Van Stappen, 1996; Hoa,

2002) Adult Artemia have an elongated body (up to about 10 mm in length in the bisexual

populations and up to 20 mm in some polyploid parthenogenetic populations) with two

stalked complex eyes, a linear digestive tract, sensorial antennae and 11 pairs of functional

thoracopods Female Artemia can be recognized by the presence of the uterus between

cephalothorax and abdomen The male can be differentiated by muscular graspers (modified 2nd antennae) in the head region, occurring from instar X onwards (Sorgeloos et al., 1980a; Jumalon et al., 1981; Criel and Macrae, 2002)

Figure 2 Life cycle of Artemia (Jumalon et al., 1981)

5 Use of Artemia in aquaculture

Over the past two decades the brine shrimp Artemia has become a key resource in the industrial expansion of fish and crustacean larviculture Annual consumption of Artemia

cysts has increased from a few tons in the mid seventies to over 2,000 tons in recent years (Sorgeloos, 2001)

The nutritional value of Artemia spp varies highly among geographical sources and even from batch to batch; especially Artemia is characterized by low contents of some essential

fatty acids (Léger et al., 1986; Lavens and Sorgeloos, 2000a; Sorgeloos et al., 1998; 2001) Hence, appropriate techniques have been developed to improve the hatchery use and

maximize the nutritional value of Artemia nauplii, taking advantage of the indiscriminate filter-feeding behaviour of Artemia (Van Stappen, 1996; Fernández, 2001; Dhont and

Sorgeloos, 2002; Lin and Shi, 2002) Apart from the application of cyst decapsulation (Garcia-Ortega et al., 2000; Lim et al., 2002) and nauplius cold storage techniques

(Merchie, 1996), Artemia has been used as vehicle for enrichment with selected fatty acids,

vitamins, essential nutrients (Léger et al., 1986; Lavens and Sorgeloos, 2000a; Sorgeloos et

al., 1998; 2001; Camargo et al., 2005) and therapeutic agents (Cook et al., 2003; Gomes et al., 2007) These developments contributed to the fast expansion of the industrial farming

of several aquaculture species all over the world

Although Artemia are mostly used under the form of freshly hatched nauplii, more and more use is made of the juvenile and adult Artemia known as biomass, collected from

natural salt lakes, salinas, man-managed pond productions and intensive culture systems for use in shrimp nursery and maturation facilities (Léger et al., 1986; Dhert et al., 1993; Merchie, 1996; Sorgeloos et al., 1998; Dhont and Sorgeloos, 2002) Furthermore, the

nutritional value of on-grown and adult Artemia is superior that of freshly-hatched nauplii,

as they have higher protein content and are richer in essential amino acids and fatty acids

(Léger et al., 1998; Bengtson et al., 1991; Lim et al., 2001; Dhont and Sorgeloos, 2002) In

recent years, the development of new aquaculture species with life-stage specific

requirements has meant diversification in the use of Artemia to include live juvenile and adults as well as frozen or dried Artemia biomass (Browdy et al., 1989; Dhert et al., 1992b;

1993; Naessens et al., 1997; Olsen et al., 1999; Wouters et al., 2002; Smith et al., 2002; Lim et al., 2003)

As more attention is given to the use of on-grown Artemia as a cheaper alternative to the

use of nauplii, simple cost-effective production techniques have been developed The use of

the right size of on-grown Artemia for feeding ensures a better energetic balance in food

intake and assimilation, thereby improving the performance of the fish and shrimp (Dhont

et al., 1993; Merchie, 1996; Lim et al., 2003) Furthermore, its palatability induces a good and fast feeding response These characteristics, coupled with the use of bioencapsulation

techniques to enhance the quality of the on-grown Artemia, make this organism an

optimum diet for nursery of the fish (Dhert et al., 1993; Merchie, 1996; Sorgeloos et al., 2001; Dhont and Sorgeloos, 2002; Lim et al., 2003)

Kim et al (1996) found that adult Artemia are highly palatable feed items for juvenile

salmonids First-feeding coho salmon, experienced significantly improved growth when fed

live adult Artemia compared with live nauplii that was likely related to the differences in

size between the two Based on energy values of 8 kcal g-1 for lipid and 5 kcal g-1 for

protein, the capture of an adult Artemia provided a fish with 240 times more energy than did the capture of a nauplii Nonetheless, most of the time, juvenile Artemia are used

instead of adults just before weaning (Lee and Litvak, 1996; Olsen et al., 1999) The study

of Ritar et al (2003) assessed the effect of Artemia prey size on the survival and growth of

rock lobster larvae They reported that survival and growth of newly-hatched lobster larvae

cultured to stage III were lower when fed 0.8 mm Artemia than 1.5 mm or 2.5 mm Artemia

In addition, survival and growth were higher between stages III and V when fed 2.5 mm

Artemia than 1.5 mm Artemia However, stage VI larvae grew to a similar size at stage VIII

when fed 1.5 mm or 2.5 mm Artemia Similar observation was reported by Lim et al (2003) the cultured on-grown Artemia with size range from 0.45 mm at inoculation to an

average length of about 5 mm was considered suitable for all sizes of freshwater ornamental fish species of up to 10 cm total length, i.e discus juveniles displayed a better

feeding response to the on-grown Artemia and showed a better growth performance and higher survival than fish fed Moina or frozen bloodworms

In postlarval stages of penaeid shrimp and clawed lobster, live Artemia biomass has been

shown to provide excellent nutrition (Conklin, 1995; Wickins and Lee 2002), although the cost of its purchase or production is prohibitive for large-scale hatchery use, the traditional

alternative has been to feed frozen adult Artemia, which supports growth rates approximately 60% of that of live Artemia (Conklin, 1995; Tlusty et al., 2005a) Moreover, survival and growth of P vannamei postlarvae fed ensiled Artemia biomass were comparable to PL fed frozen Artemia form (Abelin et al., 1991) The study conducted by Naegel and Rodriguez-Astudillo (2004) illustrated that dried Artemia is a well-suited feed for postlarval shrimp, Litopenaeus vannamei

As mentioned earlier, adult Artemia has higher nutrition value compared to nauplii and also

appears containing hormonal substances According to Naessens et al (1997), reproductive

hormones of Artemia contribute to the shrimp endocrinological cycle This could be true in

organisms that share the same hormones as Penaeid shrimp The role of hormonally active

substances has been suggested for Artemia biomass in the reproductive stage Thus frozen Artemia biomass (usually boosted with specific nutrients) has been reported to

fresh-stimulate ovarian maturation, increase spawn frequency and improve larval quality (Browdy et al., 1989; Naessens et al., 1997; Wouters et al., 1999) Additionally, it was

observed that incorporating freeze-dried Artemia biomass into an artificial broodstock diet increased diet ingestion, improved gonad maturation in female and male L vannamei, and

increased spawning performance (Wouters, 2001)

The investigations implemented by Gandy et al (2007), found that replacement of bloodworms with enriched adult Artemia as a feed for Farfantepenaeus aztecus

broodstocks resulted in higher hatch and larval survival rates (nauplius 1 to zoea 1) (55.0%

vs 46.9% and 44.8% vs 37.2%), respectively In addition, the life span of ablated females

fed adult enriched Artemia was 8 and 40 days longer than ablated females fed bloodworms

for the first and second studies, respectively Other results showed that the spent spawners

of Penaeus monodon, fed herbal enriched Artemia supplementation showed a better

reproductive performance and larval quality (Babu et al., 2008)

In Vietnam, previous investigation on the nutritional value of different forms of Artemia biomass was reported by Brands et al (1995), live Artemia biomass can be used as a

complete replacement of trash fish (fresh or cooked) for nursing of penaeid postlarvae Although the survival did not show any relation with the amount of biomass feeding, growth of nursed shrimps displayed an increasing trend with the amount of biomass

feeding Moreover, the two forms of processed Artemia biomass, frozen and ensiled, which were tested in nutritional bioassays with various aquatic species, only frozen Artemia

biomass showed an intermediate potential for application According to recent researches,

live Artemia biomass can be used as a feed for nursing mud crabs Scylla paramamosain

from instar I up to 60 days, reaching a size of 35 mm carapace width and 10.5 g body

weight (Ut et al., 2007a) Le et al (2008) found that live Artemia biomass was a very favourite food of sea-bass (Lates calcarifer) during 4 week-nursing in earthen ponds Similar observation was made by Van et al (2008), five types of Artemia biomass that were

obtained from different culture conditions consisting of four live biomass and a frozen All

of which were suitable food sources for nursing of tiger shrimp PL (Penaeus monodon) and ornamental fighting fish (Betta splendes) Preliminary observations for brackish water fish, the goby (Pseudapocryptes elongatus) broodstocks fed frozen Artemia biomass showed a better maturation than animals fed Tubifex or fresh shrimp in captivity conditions

(unpublished data)

In practice, Artemia cyst used as a live food in larviculture of prawn and shrimp accounted

for more than 50% of total operating cost of hatchery (Phuong et al., 2006b) On the other

hand, Artemia cyst prices have noticeably increased in recent years, resulting in

augmentation of the hatchery cost; hence cheaper alternative diets with comparable nutritional quality to partially replace live food are needed to maintain the cost competitiveness of shrimp in the local market in Vietnam

6 History of Artemia study in Vietnam

6.1 Geographic areas of field study

The area of Vinh Hau salt works, is situated at latitude of 9o38'9"N and longitude of

105o51'45"E and belongs to Bac Lieu province, South of Vietnam (Figure 3)

Figure 3 Location of the study area in the Mekong Delta of Vietnam

Similar to other coastal areas in the Mekong Delta, saltworks in Bac Lieu shows typical clayish soil characteristics It has a semi-tidal regime and is dominated by a rainy south-west monsoon from end of April until October (85% of the annual rainfall), and a dry north- east monsoon from November until April (15% of the annual rainfall) Diurnal temperatures fluctuate between 21 and 34oC, the maximum temperature is recorded in April-May, often exceeding 36°C Sunshine and radiation vary with the seasons: highest monthly averages occur towards the end of the dry season, from February to May (8-10 hours day-1 and 450-550 cal m-2, respectively) and are lowest from August to September/October (5-7 hours day-1 and 360-400 cal m-2, respectively) Salinity of the area fluctuates seasonally, and highest salinities are recorded from April to May, at the end of the dry season Nevertheless, incoming salinity from the main seawater supply canal is generally below 30 g L-1 Furthermore, as Artemia ponds are usually shallow and heavy

Field study

rains quickly dilute the pond salinity, pond culture of Artemia is not feasible during the

rainy season

6.2 Overview of Artemia culture in Vietnam

Since 1983, a KWT project was established between the Faculty of Fishery (Can Tho University, Vietnam) and the Dutch NGO Komitee voor Wetenschap en Techniek (Brands, 1992) This program was founded with, as one of the objectives, to develop the larviculture

of the giant fresh water prawn (Macrobranchium rosenberii) so that hatchery-produced

juveniles of prawn could be distributed to local farmers However, successful larviculture

of the fresh water prawn requires Artemia nauplii as live larval food Since Artemia is not naturally distributed in Vietnam and Artemia cysts were imported at high prices, it was decided to test and develop Artemia culture techniques in the solar saltworks during the dry season Therefore, in 1985 an Artemia Project was initiated with the support of KWT and a

field research station was set up at Vinh Tien Shrimp- Salt Cooperative, Vinh Chau district, Soc Trang province by the Faculty of Fishery

Figure 4 Evolution of Artemia cyst production in the Mekong Delta- in the period

1986-2008 (Source: College of Aquaculture and Fisheries, Can Tho University, Vietnam)

In Cam Ranh Bay (Central Vietnam) Artemia was first inoculated in 1983 (Quynh and Lam, 1987) and the first introduction with Artemia franciscana from San Francisco Bay

(SFB, USA) was made in 1986 into Vinh Chau salt fields, southern Vietnam (Rothuis, 1987) Over the years this strain showed its ability to adapt to the new habitat with high

water temperatures of Vinh Chau salt-fields as cyst yields gradually improved exceeding the amounts obtained with the original SFB (Hoa, 2002)

Since then, the interest in the seasonal culture of Artemia in view of the possibility of

harvesting cysts has grown and the know-how was transferred to a few salt farmers This alternative farming system was successful and resulted in higher profits for farmers compared to their traditional low income from the salt production In 1990, about 1.4 tonnes of raw cysts were collected from a culture area of 16 ha, which made the product available for commercialization (Brands et al., 1995) By 2001, the area covered by production sites increased up to over one thousand hectares of salt-fields in Vinh Chau and Bac Lieu coastal lines, yielding almost 50 tonnes of raw cysts (Figure 4)

This region is nowadays an important supplier of high quality cysts for domestic use and

partially for export However, from 2002 onwards the development of Artemia culture has

encountered some limitations due to a dramatic increase in production area without appropriate planning, the limited knowledge of the farmers in pond management; the large variation in economical effect within the region and the instability of the output market, apart from the effect of the unusual weather conditions (Nam et al., 2008) Resolving these

problems will be helpful for the sustainable development of the Artemia production in this

region

6.3 Perspectives for production of Artemia biomass in Vietnam

Aside from the successful production of Artemia cysts, culture of Artemia biomass for local use has also been viewed as a possible integrated economic activity, where Artemia cysts- cum-salt production is combined with a further diversification of Artemia products

(biomass), thus providing for more flexibility in the integrated systems (Brands et al., 1995;

Quynh, 1995) These authors reported that partial harvesting Artemia biomass in the large

ponds also allowed cyst collection at a rate of 30 to 75% of the cyst production ponds without biomass harvesting (Brands et al., 1995; Anh et al., 1997a; Anh and Hoa, 2004)

Moreover, at the same time the nutritional value of different forms of Artemia biomass was

assessed as a replacement, total or partial, of other traditional aquaculture feeds used in Vietnam This strategy was performed for a variety of cultured species through a series of laboratory bioassay and earthen pond culture tests (Brands et al., 1995)

Economic analysis in previous studies shows that biomass production could increase the

benefit from Artemia cyst production up to several times, depending on the cyst farm-gate price and the Artemia standing stock The salterns in Vinh Chau and Bac Lieu areas had

economic potential Other less remote salt production areas have the same potential, especially those that are in close proximity to urban areas, and/or where salt production is artisanal and consists of small ponds that are not suitable for efficient cyst production

These ponds can be used to culture Artemia biomass contributing to the farmer’s income (Brands et al., 1995) Although Artemia biomass culture has not fully developed at the

current time, the diversity of highly economic cultured species require excellent quality foods with life stage specific for hatchery and nursery phases that indicate a good chance

for near future development of Artemia biomass production in the country

7 Culture technique of Artemia biomass in salt works

According to Brands et al (1995) and Anh et al (1997a), culture system and pond

management of both Artemia biomass- and cyst-oriented production are similar, and they

only have a difference in the main product: biomass (live animals) versus cysts (dormant

eggs) The general principles of pond production of Artemia biomass in salt ponds are

briefly described as follows:

Site selection

Artemia is cultured in coastal salt works, where seawater is available during the culture

period and can easily be concentrated to produce highly saline water through the evaporation of seawater The soil should not allow leakage and seepage so that the water level is maintained and the animals will not be able to escape with the water current Vinh

Chau and Bac Lieu salt fields are suitable locations for Artemia ponds

Culture season

Artemia culture takes place in the dry season from December to May, or longer depending

on the weather and salinity in the culture ponds

Culture system

Artemia culture uses mainly the static system in which all ponds are managed separately It

consists of a reservoir, fertilization ponds and Artemia ponds with a surface area ratio of

20%, 25%, and 50-60%, respectively; and a supply canal However, this ratio can vary depending on the particular region, the tidal regime and water depth of the reservoir and

fertilization ponds

Pond design

The production system is located alongside a canal as there must be a water intake/drainage structure by which high salinity or fresh seawater can be pumped in and out anytime as the need arises The culture ponds are converted and modified from the existing salt fields

Suitable sizes of Artemia biomass ponds can range from 0.05 to 0.5 ha For new ponds,

they should be designed as follows: the peripheral ditch should be 2-3 m wide and 0.3-0.6

m deep, the dikes should be raised to 0.5-0.8 m in height and a supply canal should have a width of 1-1.5 m The pond must be constructed in such a way that it can hold at least 40

cm of water depth from the platform

Pond preparation

The preparation of the culture ponds starts in December when the rainy season is over All ponds are drained completely and the pond bottom and canals are scraped and sun dried for about 5 to 7 days About 10-15 kg of lime 100m-2 should be spread over the pond bottom and the pond is then left to dry for about 2 to 3 days if the pH is low (pH <8) Derris root was applied at 1 kg 100m-3 to kill predators before inoculating Saline water used to fill the ponds is filtered through a 500 μm nylon screens to eliminate fish eggs and larvae

Saline preparation

After drying the pond bottom, water is allowed into the ponds and left to evaporate The whole surface area can be used for water evaporation It takes about 3 to 4 weeks to reach a salinity of ≥ 80g L-1 for inoculation of the first pond For the next ponds it will take about 3

to 7 days for inoculation At the start of the culture period, the water level in the ponds is about 4-5 cm above the platform and is then gradually increased up to >40 cm during the

culture period In order to increase the availability of the natural food for Artemia, culture

ponds should be fertilized with urea and super phosphate at the rate of 1 and 0.2 g m-2 two

days before inoculation to stimulate phytoplankton bloom

The optimal conditions for Artemia cyst hatching incubation are as follows (Van Stappen,

1996):