COMMUNICATIONS (continued)

IMPROVED LARVICULTURE OUTPUTS OF MARINE FISH SHRIMP AND PRAWN

P.SORGELOOS and PH. LÉGER
BELGIUM

Much progress was made in the late 1980s in the commercial and experimental larviculture of different species with aquaculture interest, e.g., different species of penaeid shrimp, Macrobrachium prawn, European and Asian bass and bream species, Japanese flounder, Atlantic turbot and halibut, Pacific mahimahi, Improved nutrition, especially through the application of enrichment diets for enhancing the nutritional value of the live feed organisms Brachionus plicatilis and Artemia spp., as vell as the use of live feed supplements and substitues, and the application of improved zootechnical methods, all have contributed to a significant increase in larval survival and quality. Better and more predictable hatchery outputs at reduced production costs offer higher guarantees for successful commercial larviculture. More competitive industrial larviculture, especially with the marine fish species will only be possible by further improvements in larval nutrition, zootechnical aspects and disease diagnosis as well as control.

Dependable availability of fry, fingerlings or postlarvae is one of the critical factors in the commercial success of the industrial production of marine fish or crustaceans (FAO 1989). Only for a few species with unique ecological and ethological characteristics can wild sources of seed be used for the stocking of growout ponds or cages, For example, in Ecuador penaied shrimp postlarvae are being collected from coastal area by the billions per year. This cheap source of readily available seed has been at the origin of the multimillion US dollar shrimp farming industry in Ecuador (Lee 1989). Only wild fry are used for annual production of several hundred thousand tons each of the milkfish Chanos chanos in the Philippines and Indonesia and the yellowtail Seriola quinqueradiata in Japan. However, when wild penaeid seed provisions suddenly decreased a number of years ago in Ecuador, extended pond areas could not be kept in operation (Spurrier 1988). Milk-fish and penaeid shrimp farming in the Philippines are often restricted because of seasonal fry shortages. The Japanese government resorted to restrictions on yellowtail cage farming to prevent overfishing of wild fry resources.

When applying intensive growout techniques, shrimp farms need to operate at maximum capacities in order to show a good profit and therefore require guaranteed provisions of shrimp postlarvae on a year-round basis. In recent years several species of marine fish (e. g.,several bass and bream species, mahimahi, turbot, halibut, etc.) have been identified as new aquaculture candidates. Their growout in cages or land based systems have proven to be commercially attractive provided a regular supply of fry can be guaranteed. For most fish and crustaceans with aquaculture potential this can only be realized by the domestication of the species,i.e., the developement of appropriate techniques for controlled reproduction and larviculture.

Larviculture nutrition particularly first feeding by the early larval stages, appears to be the major bottle-neck for the industrial upscaling of the aquaculture of fish and shellfish. With a few selected species such as salmon, minimal problems had to be overcome. Within a few years billions of hatchery produced fry were used in the commercial production of over 100,000 tons of marketable salmon per year. The early development of salmon does not involve feeding problems as the larvae at hatching carry a large yolk sac with enough food reserve for the first three weeks of their development. Once the yolk is consumed and exogenous feeding begins, larvae already have a large month and can thrive on formulated feeds. With most other marine fish, egg production might not pose the major problem, but larval size at hatching and first feeding is at the origin of farming difficulties (Table 1). Most marine fish with aquaculture potential have very limited yolk reserves at hatching, mostly lasting for not more than one or two days. At first feeding they still have small mouths, often with an opening of less than 0.1 mm (Glamuzina et al, 1989; Kohmo et al 1988). In shrimp larvae feed size is not the only problem; larvae pass through different larval stages changing from a herbivorous filter into a carnivore.

Table 1. Size of eggs and larval length at hatching in different species of fish (Jones and Houde 1981)

The natural diet of most aquaculture fish and crustacean species consists of a wide diversity of phytoplankton species (diatoms, flagellates, etc) and zooplankton organisms (copepods, cladocerans, decapod larvae, etc,) found in great abundance in the natural environment. Relaying on the collection of wild plankton as a larval food source in intensive aquaculture has proven neither to be a relable nor a commercially feasible strartegy. Over the past two to three decades trial and error approaches have resulted in the adoption of selected larviculture diets. This science has been very empirical and can a posteriori elegantly be split up in selection criteria that best suit either the larvae's requirements or the farmer's restrictions (fig.1).

Today three groups of live diets are widely applied in industrial larviculture of marine fish and crustaceans :1) different species of 2–20 μm large micro algae; 2) the 50–200 rotifer Brachionus plicatilis; 3) the 200–500 μm brine shrimp Artemia spp. In years different formulations of supplementation and substitution products have been added to this list.

MICROALGAE

Diatoms and green algae are the two dominant groups of cultured microalgae (De Pauw and Pruder 1986). Food species have been selected on the basis of their mass culture potential,cell size, digestibility, and overall food value, much more by trial and error than any other scientific selection process.

The most suitable species still pose many problem for large scale culture, not least with regard to contamination problem. As a result most farms still apply labor intensive and expensive batch production systems. Even when production targets can be maintained with regard to cell numbers produced, shrimp farmers for example have experienced temporal variations in algal food values resulting in inconsistent hatchery outputs (R. Chamorro, personal communication).

LARVICULTURE OF MARINE FISH, SHRIMP AND PRAWN

Figure 1 : Selection criteria for larval foodsources from the viewpoint of the culturist and the cultured larva (Mèger et al. 1987a)

Olsen (1989) reviewed the literature and illustrated that the content of the (n-3) highly unsaturated fatty acids (HUFA's) 20:5(n-3) and 22:6(n-3) can greatly very among algal species but even from culture to culture within a given species (Fig. 2). Using penaeus stylirostris as a test organism, Léger et al. (1985a) demonstrated that the content of 20:5(n-3) and 22:6(n-3) in the zoea diet had a major impact on survival and growth in later stages, when animals had already been switched to another diet (Fig,.3). This provided the rationale to look for alternative or supplements to live microalgae. Today different approaches and formulations are already being applied at the commercial level, and many new development in more cost-effective products are to be expected, Freeze-dried algae (Taylor 1990), manipulated yeasts (Léger et al 1987b; Léger and Sorgeloos, in press; Coutteau et al. 1989), micro-encapsulated feeds (Jones et al. 1979), and different kinds of microparticulate diets (Langdon and Waldock 1981 ; Kanazawa et al. 1982; Chamberlain 1988) are gradually reducing the need for and might eventually totally replace the microalgae in commercial larviculture in the near future.

THE ROTIFER BRACHIONUS PLICATILIS

Rotifers are mostly used as a starter diet in marine fish larviculture (Fukusho 1989). Their culture appears to be simple, with microalgae (often Chlorella spp.) supplemented with bakers' yeast as their feed. However, many fish hatcheries have reported that they experience considerable problems in maintaining large culture and producing on a predictable basis the massive numbers of rotifers that are needed to feed the hundreds of housands to millions of baby fish they have in culture.

Besides zootechnical aspects (e.g., water management) food appears to be one of the key elements in the successful mass production of rotifers. For convenience, fresh bakers' yeast is mostly used as the main diet ingredient. However, its freshness, a criterion which is difficult to evaluate by the farmer, can greatly influcence the dietary value of the yeast for the rotifers, and as a consequence determine rotifer culture success. Many farmers supplement the baker's yeast with microalgae, a procedure which at the same time ensures an increase of the level of (n-3) essential fatty acids in the rotifers. This (n-3) HUFA enrichment is critical in enhancing the food value of the rotifers for marine fish larvae (Fukusho 1989).
Different microparticulate (Rimmer and Reed 1989) and emulsified formulations (Watanabe et al. 1983; Léger et al. 1987c, 1989) are used as a booster of essential fatty acids and other components. The treatment is performed for 4 to 24 hours prior to feeding the rotifers to the fish larvae. A new tendency is to simplify procedures by using feed-products for the combined culture and enrichment of Brachionus (Komis et al.1989).

Figure 2: Contest of the essential fatty acids 20 : 5(n-3) in marine diatoms green algae and dinoflagelattes (Olsen 1989).

Figure 3 : Effect of (n-3) HUFA content in the larval diet on postarval survival in Penaeaus stylirostris (modified after Léger et.al. 1985 a).

THE BRINE SHRIMP ARTEMIA SPP.

Of the live diets used in larviculture, brine shrimp Artemia nauplii constitute the most widely used species. Although its production and use appear to be most simple, considerable progress has been made in the past decade in improving and increasing its value as a larval diet. It appeared indeed that many small details in hatching procedures, which in the past have often been overlooked, e.g., light and pH, could significantly affect cyst hatching outputs (Sorgeloos 1980; Sorgeloos et al. 1986). The optimization in Artemia cyst use was also realized by the commercial provision of high quality cysts products. Although recent harvests of cysts have been plentiful, particularly at Great Salt Lake (Utah, USA), increased competition in the market has contributed to the development of improved methods for cyst cleaning and processing, resulting in the adoption of a more rigorous quality control (Bengston et al. 1991).

Better knowledge of he biology of Artemia was at the orgin of the development of methods for cyst disinfection and decapsulation (Sorgeloos et al. 1986). These procedures are being applied at several large fish and shrimp hatcheries to sterilize the cysts and remove the shells as to reduce the problems at naupliar harvest.

For a long time farmers have overlooked the fact that Artemia nauplii in their first stage of development cannot take up food and thus consume their own energy reserves. At the water temperatures which are applied for cyst incubation, the freshly-hatched Artemia nauplii develop into the second larval stage within a matter of hours, eventually losing up to 30% of their energy reserves and food value (Benijts et al. 1976). This is not only a significant financial loss for the farmer, as he has to consume up to 30% more cyst product to produce the same quantity of food, he is furthermore feeding his fish or shrimp with a less suitable prey as the older Artemia have grown bigger, swim faster, are less visible, and have a reduced food value. Therefore, rigorous standardization of hatching procedures is a must. The cyst should be incubated at constant water temperature and the nauplii harvested when they are still in their most nutritious stage. Several hatcheries have switched to a practice of daily multiple hatching and separation procedures. An easier and already common practice is to apply cold storage of the freshly-hached nauplii in concentrations of several million nauplii per liter at temperatures of 5–10 C (Léger et.al. 1983). Aeration needs to be provided in order to prevent suffocation of the Artemia which barely move at these cold temperatures and eventually sink to the bottom of the container. Applied for periods of 24 h or even longer the cold-stored Artemia remain viable without consuming their energy reserves. This allows the farmer not only to ensure the availability of a better quality product but at the same time to consider more frequent food distribution from the single hatching. This appeared to be benefical for fish and shrimp larvae as food retention times in the larviculture tanks can be reduced and hence growth of the Artemia in the culture tank can be minimized. For example, applying one or even two feedings per day, shrimp farmers often experienced growth of the Artemia in their larviculture tanks so that the Artemia and shrimp were competing for algae.

Easy hatching and disinfection procedures, however, appeared not to be the sole parameters in ensuring the success of using Artemia as a larval food source. Several other Artemia characteristics may influence the suitability of a particular brine shrimp product for one or another type of larviculture. One of these is nauplius size which can greatly vary from one geographical source of Artemia to another (Vanhaecke and Sorgeloos 1980). This is particularly critical for several species of marine fish that have a very small mouth size and swallow their prey in one bite. For example, using the marine silverside Menidia menidia as a test-organism, Beck and Bengtson (1982) were able to illustrate a high correlation between Artemia nauplius size and larval fish mortality during early development; with the largest strains of Artemia, up to 50% of the fish could not ingest their prey and starved to death. Another important dietary characteristic was identified in the late 1970s to early 1980s when many fish and shrimp farmers reported unexpected problems when switching from one geographical source of Artemia to another (Sorgeloos 1980). Japanese, American and European researchers studied these problems and soon confirmed variations in nutritional value of different geographical sources of Artemia for fish and shrimp species (Watanable et.al. 1983; Léger et al. 1986). The situation became more critical when significant differences in production yields were obtained with distinct batches of the same geographical origin of Artemia Multidisciplinary studies in Japan (Watanabe et. al. 1983) and by the International Study on Artemia (Léger et al.) 1985b, 1987a) revealed that the concentration of the essential fatty acid eicosapentaenoic acid (EPA) 20:5 (n-3) in the Artemia nauplii determines the nutritional value of this particular batch of Artemia for the larvae of various marine fish and crustacean species. Fig. 4 illustrates the results obtained with different batches of the same geographical Artenia source, containing different amounts of EPA and yielding proportional results in growth and survival of Mysidopsis bahia fed these Artemia.

Figure 4. Linear relationship between the 20:5(n-3) content of several Artemia collections from San Francisco Bay orgin and the biomass of Mysidopsis bahia to which the freshly hatched Artenia were fed (Léger et.al. 1987a)

Table 2: Intra-strain variability of 20:5 (n-3) content in Artemia. Data represent the range (area percent) and coefficient of variation of data as complied by Léger et.al. 1986 and 1987a.

As can be seen in Table 2, EPA levels in Artemia can greatly vary, even from one batch to another within the same strain. Cyst products from inland sources appear to be more constant in composition, however, at low levels of EPA. As a result concentrations of the (n-3)HUFA EPA need to be taken into consideration when selecting the most appropriate batch of Artemia cysts. In this respect the introduction of quality certificates to characterize commercial batches of Artemia cysts is highly recommended.

Commercial provision of small-size Artemia cyst containing high EPA-levels are limited. Their use, therefore, should be limited to the feeding period when size of the prey is most critical. Indeed even the best natural Artemia products do not meet all the nutritional requirements of the predator larvae, most particulary with regard to the other essential fatty acid for marine organisms, docosahexaenoic acid (DHA) 22.6 (n-3), which is never available in significant amounts in Artemia cysts (Léger et.al. 1986; Bengtson et al. 1991).

It is fortunate that Artemia, because of its primitive feeding characteristics, allows a very convenient way to manipulate its biochemical composition. Since Artemia, once it has molted into the second larval stage (i.e., about eight hours following hatching), is non-selective in taking up particulate matter, simple methods have been developed to incorporate any kind of product into the Artenia prior to offering it as a prey to the predator larva. This method of «bio-encapsulation», also called Artemia enrichment or boosting, is widely applied at marine fish and crustacean hatcheries all over the world for enhancing the nutritional value of Artemia with essential fatty acids, British, Japanese and Belgian researches developed enrichment products and procedures using selected microalgae and/or micro-encapsulated products, yeast and/or emulsified preparations, using self-emulsifying concentrates and/or micro-particulate products respectively (Léger et.al. 1986;Bengston et.al. 1991). The highest enrichment levels in Artemia as well as in the rotifer Brachionus are obtained when using emulsified concentrates (Table 3) (Léger et.al. 1987a; Bengtson et.al.1991).

PROGRESS IN LARVICULTURE NUTRITION

The use of (n-3) HUFA - enriched Artemia as a more adequate food source has without any doubt been at the origin of a real break-through in the larviculture of many marine fish species (Watanabe et.al. 1983; Sorgeloos et.al. 1987, 1988). For example, for the European bass Dicentrarchus labrax and seabream Sparus aurata, the adoption of this «bio-encapsulation» methodology has allowed the transition from pilot to commercial larviculture of these species (Frentzos and Sweetman 1989). The effects of feeding (n-3) HUFA-enriched Artemia and Brachionus indeed are significant. Dicentrachus larvae died off before day 35 when fed (n-3) HUFA-deficient, freshly-hatched Artemia nauplii from Great Salt Lake cysts (Van Ballaer et.al. 1985). Enriched Artemia of the same batch fed to the larvae resulted not only in increased survival but also in the production of bigger larvae which better resisted stress conditions (Franicevie et.al. 1987).

Similar observations of increased survival and growth when feeding (n-3)HUFA-enriched diets have been confirmed for several species of panaeid shrimp where sometimes effects of diet composition only came to expression in later stages (Léger et.al. 1987b; Tackaert et al. 1989; Léger and Sorgeloos, in press). A good illustration of this is the resistance to salinity stress in PL-10 stages of a batch of Penaeus monodon fed on three different larval diets that varied in (n-3)HUFA levels. Differences in survival among the three treatments were not significant at PL-10 before the stress test. However, differences in PL quality, expressed as their ability to survive the salinity stress applied, were very pronounced (Fig. 5). resistance to salinity shocks, which can easily be applied at the hatchery level, is now being used as a quality criterion for determining the appropriate time for PL transfer from the hatchery to the ponds (Sorgeloos 1989).

With the freshwater prawn Macrobrachium rosenbergii; (n-3)HUFA-requirements of the larvae were anticipated not to be very critical in view of the fact that they spend most of their life in freshwater. These assumptions, however, were largely contradicted by the results of Devresse et.al. (1990) and Romdhane et.al. (1990) who used Artemia enriched with different (n-3)-HUFA emulsions. Besides the improved growth rate, a distinct difference having an important impact for the commercial farmer was the more precocious and more synchronous metamporphosis as well as the higher stress resistance of the Macrobrachium postlarvae that had received (n-3)HUFA-enriched Artemia in the larval stages.

Table 3. (n-3) HUFA content in rotifers (Brachionus plicatilis) and Artemia enriched with different products (Léger et.al. 1989)

^a mg fatty acid methyl ester per gram dry weight rotifer or Artemia
^b self emulsifying (n-3)HUFA enrichment concentrates (Artemia Systems, S.A., Ghent, Belgium).
^c protein based (n-3)HUFA enrichment product (Artemia Systems, S.A., Ghent, Belgium).

Figure 5. Survival of Penaeus monodon PL-10 cultured on larval diet combinations that contained low, medium and high levels of (n-3)HUFA's after 60 min transfer from 35 ppt to 7 ppt seawater Tackaert et.al. 1989).

Where as for a number of species larviculture outputs have been improved developments in nutritional manipulation of the live feeds (various papers presented at the Larviculture Special Session of Aquaculture '90 Halifax, Canada), with other species such as mahimahi, turbot, halibut and others, research is still in progress to better define quantitative (n-3)HUFA requirements; it appears that for many species of marine fish optimal dietary levels have not been reached yet in Brachionus and Artemia. Furthermore, although (n-3) HUFA's might have proven most critical so far, other nutrients, e. g. other lipid classes, particular peptides, free amino acids, pigments, sterols and vitamins might appear equally important and in some species may be more critical. In view of the better results obtained with the use of natural plankton, consisting mostly of marine copepods, in culturing turbot and mahimahi (S. Kraul, personal communcation), the challenge remains to idenify the vital components in copepods in order to have these incorporated in the convenient dietary system consisting of enriched Brachionus and Artemia.

Figure 6. Artemia concentrator-rinsor as manufactured by Artemia Systems SA, Ghent, Belgium (Léger and Sorgeloos, in press).

ZOOTECHNICAL ASPECTS

In the past five years the number of capacities of marine fish and crustacean hatcheries have escalated all over the world. The intensification of hatchery activities, however, brough about several new problems not seen at an experimental scale. For example, skeletal deformities and absence of swim bladder inflation, long blamed to be genetic disorder, appeared to be caused by imperfect zootechnical procedures (Foscarini 1988). An invisible oil-film at the tank's surface hampered the larval fishes' ability to gulp air and fill their swim bladders. As a result, these fish needed to spend more swimming efforts to stay in the water column, which eventually caused spinal deformities. These problems are largely overcome today by applications of more rigorous washing procedures of the live food, especially after enrichment with the high lipid containing products. New equipment and materials were introduced in the hatcheries. For example, welded wedge filers (Fig. 6) are not only very efficient in washing and cleaning; at the same time they guarantee that the Artemia are not physically damaged during this process. Oil skimmers (Fig.7) installed in the fish culture tank ensure final prevention of the build-up of an oil film, which might also be enhanced by algae metabolites when applying the green water technique.

SORGELOOS AND LÉGER

Figure 7. Shematic drawings of four types of surface cleaners used in Europe in the larviculture of seabass Didentarchus labrax and seabream Sparus aurata: A) model fixed to the side (BB) of the culture tank: B) C) and D) are floating models; the arrow shows the distribution of compressed air (Dewavrin and Chauveau 1990).

DISEASE PROBLEMS

Bacterial and viral outbreaks have caused enormous interferences in the successful industrialization of fish and crustacean larviculture, lack of basic hygienic precautions has been and still is at the origin of most problems (Brown 1989); however, all kinds of chemotherapeutics are applied both for desease prevention and treatment. Products have been used following trial and error procedures, not based at all upon expert advice. A wide range of broad spectrum antibiotics became routine application in shrimp and marine fish operations. Products such as chloramphenicol, tetracycline, and furazolidone are often applied at daily doses up to 50 ppm in the case of marine fish. Short-term benefits soon turned into disasters. Worst affected has been the shrimp culture industry in which at some times and places all larviculture activity had to be suspended (Chamberlain 1988).

Although there is still much room for improvement, not the least by a better identification and documentation of the disease problems, better preventive measures are being implemented. For example, routine disinfection procedures of culture tanks and live food culture facilities, as well as regular dryouts between two to three consecutive larviculture runs, are widely adopted now and have resulted in more predictable hatchery outputs.

In marine fish larviculture it appears that microbial problems are less critical in those hatcheries that are operating recirculation systems using biological filters. In this respect there is a great need to document the microbial environment in fish and crustacean hatcheries not only at critical moments but also when outputs are optimal.

As was recently demonstrated, the bioencapsulation methodology with Artemia and Brachionus can also be considered for more effective transfer of therepeutics through oral administration of antibiotics (Léger et al. 1990).

FUTURE PROSPECTS

In the past decade marine fish and crustacean hatcheries have evolved from hit and miss ventures into profitable ventures. With many fish species the larviculture industry has not yet reached the state of competitive maturity. In Europe, for example, the situation is artificial because fry outputs cannot meet present demands. As a result hatcheries can sell their fingerlings at prices that range from approximately 1 US dollar per individual fingerling of bass and bream up to 4 US dollars per turbot fry. Profit margins are high; however, one should not forget that many of the these hatcheries have lost money for years when they were pioneering marine fish larviculture. The number of marine fish hatcheries is increasing very fast in Europe and the ones already in operation are steadily increasing their capacities (Artemia Systems NV/AS, personal communication). The situation may soon turn, similarly to what has been experienced in recent years with the prices of salmon smolts and penaied shrimp postlarvae. In Taiwan, Thailand, and Ecuador, market prices of Penaues mondodon and P. vannamei crashed from a year-long top price 20 US dollars per 1,000 PL to extremely competitive prices of a few dollars only. Big hatcheries with high investment and over-head costs may only remain viable if they can operate on a year-round basis and at maximal efficiency. Some of the big operations in Ecuador for example manage to yield survival rates exceeding 80% at harvest of the PL's

Backyard hatcheries (e.g., in Thailand and Indonesia) are a peculiar phonomenon as these are mostly hit and miss operations (Yap 1990). They are managed with limited expertise, mostly under poor water quality and hygienic standards. Nonetheless they have become more and more important and mushroomed into the thousands during the last couple of years in some SE Asian countries. As these family activities involve minimal operational costs they can afford low success rates and still remain profitable at PL prices which are beyond the limits for profitable production by the large hatcheries. However, they impose considerable risks for total collapses of local aquaculture activities as was the case with the once very successful shrimp farming industry in Taiwan (Liao 1989). In order to become a stabilized industrial activity that meets the requirements of local growout capabilities the larviculture of marine fish and crustaceans needs to further improve its outputs. With survival rates in marine fish larviculture rarely reaching 20–30%, it is clear that there is still much room for improvement and increased cost-effectiveness. In the short term the following fields need more exploration: 1) how can egg quality be better defined and controlled?; 2) present knowledge about qualitative and quantitative nutritional requirements is still very limited for most species; 3) too limited attention has been paid to zootechnical aspects in relation to upscaling, automation, recirculation systems, intensive versus extensive systems, etc.; and 4) better understanding of the microbial environment in the hatchery as well as the larval immune system will allow better management with ragard to disease prevention and control.

A final remark needs to be made regarding feeding strategies in larviculture, more particularly the future of live feeds versus formulated feeds. Off-the-shelf dry products are being developed and commercialized as a much more convenient application for the farmer. With some species, such as penaied shrimp, the moment is approaching for reducing live algae and Artemia feeding to virtual elimination from the hatchery operation. Other species, such as marine fish species, impose much more constraints than shrimp, not only in terms of nutritional requirements but also with regard to physical properties of the feed, e.g., water stability, buoyancy, paatability, etc. Appropriate process technologies will certainly be developed but their commercial applicability and price competitiveness might not be obvious. Feeding strategies in hatcheries of marine fish and crustaceans will probably never be standardized world-wide because of species difference and geographical discrepancies. The cost-effectiveness of live and formulated feeds will dictate their proportional use.

ACKNOWLEDGMENTS

This research has been sponsored by the Belgian National Science Foudation, the Belgian Administration for Development Cooperation, the Belgian Ministry for Science Policy, and the Belgian Company Artemia Systems S.A.

LITERATURE CITED

BECK, A.D. and D.A.BENGTSON. 1982. International study on Artemia XXII. Nutrition in aquatic toxicology — diet quality of geographical strains of Artemia pages 161–169 in J.G. Pearson, R.B. Foster and W.E. Bishop, editors. Aquatic toxicology and hazard assessment. 5th Conference, ASTM STP 766. American Society of Testing and Materials. Philadelphia, Pennsylvania, USA.

BENGTSON, D.A., P. LÉGER and P. SORGELOOS. 1991. Use of Artemia as a food source for aquaculture. Chapter 11. Pages 255–285 in R. A. Browne, P. Sorgeloos and C.N.A. Trotman, editors, Artemia biology. CRC Press, Boca Raton, Florida, USA.

BENIJTS, F., E. VANVOORDEN and P. SORGELOOS. 1976. Changes in the biochemical composition of the early larval stages of the brine shrimp, Artemia salina L. Pages 1–9 in G. Persoone and E. Jaspers, editors. Proceedings of the 10 th European Symposium on Marine Biology, volume 1. Research in mariculture at laboratory and pilot scale. Universal Press, Watteren, Belgium.

BROWN, J. 1989. Antibiotics: their use and abuse in aquaculture. World Aquaculture 20 (2): 34–43. Chamberlain, G. 1988. Shrimp hatcheires. Coastal Aquaculture (1).

COUTTEAU, P., P. LAVENS and P. SORGELOOS. 1990. The use of yeast as single-cell protein in aquacultural diets. Medical Faculty of Landbouww. Rijjsuniv. Gent, 54 (4b). 1989.

DE PAUW, N. AND G. PRUDER, 1986. Use and production of microalgae as food in aquaculture: practices, problems and research needs. Pages 77–106 in M. Bilio, H. Rosethal and C.J. Sinderman, editors. Realism in aquaculture: achievements, constraints, perspectives. European Aquaculture Society, Bredene, Belgium.

DEVRESSE, B., M. ROMDHANE, M. BUZZI, J. RASOWO, P. LÉGER, J. BROWN and P. SORGELOOS. 1990. Improved larviculture outputs in the giant freshwater prawn Marcrobrachium rosenbergii fed a diet of Artemia enriched with (n-3)-HUFA and phospholipids. World Aquaculture 21(2):123–125.

DEWAVRIN, G. and H. CHAUVEAU. 1990. Ecrémeurs de surface. Aqua Revue 29: 25–26.

FAO. 1989. Planning for aquaculture development. ADCP/REP/89/33, FAO, Rome, Italy.

FOSCARINI, R. 1988. A review: intensive farming procedure for red sea bream (Pagrus major) in Japan. Aquaculture 72:191–246.

FRANICEVIC, V., D. LISAE, J. BUBLE, P. LÉGER and P. SORGELOOS. 1978. Etude internationale sur l'Artemia. XLII. L'effet de la qualité nutritionelle de l'Artémia sur la croissance et la survie des larves du loup (Dicentrarchus Labrax L.) dans une écloservie commerciale. Pages 139*-145 in B. Loix, editor. Production in marine hatcheries. FAO-MED-RAP, Rovinj-Zadar, Yugoslavia.

FRENTZOS, T. and J. SWEETMAN. 1989. An integrated marine fish farm in Cephalonia, Greece. Pages 143–153 in N. De Pauw. E. Jaspers, H. Ackefors and N. Wilkins, editors. A biotechnology in progress. European Aquaculture Society, Bredene, Belgium.

FUKUSHO, K. 1989. Biology and mass production of the rotier Brachionus plicatilis, International Journal of of Aquaculture and Fisheries Technology 1:232–240.

GLAMUZINA, B., J. JUG-DUJAKOVIE and I. KATAVIC. 1989. Preliminary studies on reproduction and larval rearing of common Dentex, Dentex dentex (Linnaeus 1758). Aquaculture 77:75–84.

JONES, D.A., A. KANZAWA and K. ONE. 1979. Studies on the nutritional requirements of the larval stages of Penaeus Japonicus using microencapsulated diets. Marine Biology 54:261–267.

JONES, A. and E.D. HOUDE. 1981. Mass rearing of fish fry for aquaculture. Pages 351–374 in M. Bilio, H. Rosenthal and G. J. Sinderman, editors. Realism in aquaculture: achievements, constraints, respectives. European Aquaculture Society, Bredene, Belgium.

KANAZAWA, A.S. TESHIMA and H. SASADA. 1982. Culture of prawn larvae with microparticulate diets. Bulletin of the Japanese Society of Scientific Fisheries 48(2)L:195–199.

KOHNO, H., S. HARA, M. DURAY and A. GALLEJO. 1988. Transition from endogenous to exogenous nutrition sources in larval rabbitfish Siganus guttatus. Nippoon Suisan Gakkaishi 54(7): 1083–1091.

KOMIS, A., E. NAESSENS, E. VAN BALLAER, P. VAN SPRANG. P. LéGER and P. SORGELOOS. 1989. New developments in the mass culture and nutritional enrichment of the rotifer Brachionus plicatilis using artificial diets. European Aquaculture Society, Special publication, number 10. Bredene, Belgium.

LANGDON, C.J. and M.J. WALDOCK. 1981. The effect of the algal and artificial diets on the growth and fatty acid composition of Crassostrea gigas spat. Journal of the Marine Biological Association of the U.K. 61:461–448.

LEE, D. 1989. Why Ecuador is among world leaders in shrimp farming. Fish Farming International 16(4):22–24.

LÉGER. P. 1989. The nutritional value of Artemia in aquaculture. Doctorate thesis. Stage University of Ghent Belgium.

LÉGER, P., D.A. BENGTSON, K.L. SIMPSON AND P. SORGELOOS. 1986. The use and nutritional value of Artemia as a food source. Oceanography and Marine Bology: An Annual Review 24:521–623.

LÉGER, P., D.A. BENGTSON, P. SORGELOOS, K. L. SIMPSON and A.D. BECK. 1987a. The nutritional value of Artemia: a review. Pages 357–372 in P. Sorgeloos, D.A. Bengtson, W. Decleir and E. Jaspers, editors, Artemia research and its applications volume 3. Universa Press, Watteren, belgium.

LÉGER, P. G.F. BIEBER and P. SORGELOOS. 1985a. International study on Artemia. XXXIII. Promising results in larval rearing of Penaeus stylirostris using a prepared diet as alga substitute and for Artemia enrichment. Journal of the World Aquaculture Society 16:354–367.

LÉGER, P., R.CHAMORRO and P. SORGELOOS. 1987b. Improved hatchery produciton of postlarval Penaeus vannamei through application of innovative feeding strategies with and algal substitute and enriched Artemia. Paper presented at the 18th Annual Meeting of the World Aquaculture Society, Guayaquil (Ecuador), January 18–23, 1987.

LÉGER, P., D. GRYMONPRÉ, E. VAN BALLAER and P. SORGELOOS. 1989. Advances in the enrichment of rotifers and Artemia as food sources in marine larviculture. Pages 141–142 in Aquaculture Europe `89. Short Communications. Abstracts. European Aquaculture Society Special Publication, number 10. Bredene, Belgium.

LÉGER, P., E. NAESSENS-FOUCQUART and P. SORGELOOS. 1987c. International study on Artemia. XXXV. Techniques to manipulate the fatty acid profile in Artemia nauplii and the effect on its nutritional effectiveness for the marine crustacean Mysidopsis Bahia (M). Pages 411–424 in P.Sorgeloos, D.A. Bengtson, W. Decleir and E. Jaspers, editors. Artemia research and its applications, volume 3. Universal Press, Watteren, Belgium.

LÉGER, P., P.SORGELOOS, O.M. MILLAMEAN and K.L. SIMPSON. 1985b. International study on Artemia. XXV. Factors determining the nutritional effectiveness of Artemia: the relative impact of chlorinated hydrocabons and essential fatty acids in San Francisco Bay and San Pablo Bay Artemia. Journal of Experimental Marine Biology and Ecology 93:71–82.

LÉGER, P. and P. SORGELOOS. In press. Optimized feeding regimes in shrimp hatcheries in A.W. Fast and L.J. Lester, editors. Culture of marine shrimp: principles and practices.

LÉGER, P., P. VANHAECKE and P. SORGELOOS. 1983. International study on Artemia. XXIV. Cold storage of live Artemia nauplii from various geographical sources: potentials and limits in aquaculture. Aquacultural Engineering 2:69–78.

LÉGER, P., R. VERPRAET, H.J. NELIS, A.P. DE LEENHEER and P.SORGELOOS, 1990. Live food mediated drug delivery as a tool for disease treatment in larviculture. 1. The enrichment of sulfadrugs in rotifers and Artemia nauplii a case study. Page 23 in Book of abstracts. World Aquaculture 1990, June 10–14 Halifax, Nova Scotia, Canada.

LIAO, I.C. 1990. The world's marine prawn culture industries: today and tomorrow. Pages 11–27 in R. Hirano and I. Hanyu, editors. Proceedings of the 2nd Asian Fisheries Forum. The Asian Fisheries Society, Manila, Philippines.

OLSEN, Y. 1989. Cultivated microalgae as a source of omega-3 fatty acids. Pages 15–18 in Fish, fats and your health. Proceedings of the International Conference on Fish Lipids and Their Influence on Human Health. Svanoy Foundation, Norway.

RIMMER, M.A. and A. REED. 1989. Effects of nutritional enhancement of live organisms on growth and survival of Barramundi/Seabass Lates calcarifer (Bloch) larvae. AQUACOP IFREMER Actes de Colloque 9:611–623.

ROMDHANE, M.S., B. DEVRESSE, P. LÉGER, and P. SORGELOOS. 1990. Effects of feeding nutritionally enriched Artemia during a progressively increasing period on the larviculture of the freshwater prawn Macrobrachium rosenbergii. Paper presented as Aquaculture `90, Halifax, Canada, June 1990.

SORGELOOS, P. 1980. The use of the brie shrimp Artemia in aquaculture. Pages 25–46 in G. Persoone, P. Sorgeloos, O. Roels and E. Jaspers, editors. The brine shrimp Artemia, volume 3. Ecology, culturing, use in aquaculture. Universa Press, Wetteren, Belgium.

SORGELOOS, P. 1989. Stress resistance in postlarval penaeid shrimp. Artemia Newsletter, State University of Ghent, Belgium 12:12–13.

SORGELOOS, P., P. LAVENS, P. LÉGER, W. TACKAERT and D. VERSICHELE. 1986. Maunal for the culture and use of brine shrimp Artemia in quaculture, Artemia Reference Center, State University of Ghent, Belgium.

SORGELOOS, P., P. LÉGER, and P. LAVENS. 1988. Improved larval rearing of European and Asian seabass, seabream, mahi-mahi, siganid and milkfish using enrichment diets for Brachionus and Artemia. World Aquaculture 19(4):78–79.

SORGELOOS, P., P. LÉGER, P. LAVENS and W. TACKAERT. 1987. Increased yields of marine fish and shrimp production through application of innovative techniques with Artemia. Aquaculture et Développement, Cahiers Ethologie Appliquée 7:43–50.

THE USE OF BRINE SHRIMP ARTEMIA IN BIOLOGICAL MANAGEMENT OF SOLAR SALTWORKS

WIM TACKAERT¹ AND PATRICK SORGELOOS^2
1SALT LAKE BRINE SHRIMP, INE, GRANTSVILLE, UTAH, USA
²LABORATORY OF AQUACULTURE AND ARTEMIA REFERENCE CENTER, UNIVERSITY OF GHENT, BELGIUM

ABSTRACT

In recent years, there has been a growing awareness of the hydrobiological aspects of the solar salt production process. Saltworks are man-managed artifical ecosystems that are highly vulnerable to biological disturbances, including uncontrolled proliferation of microalgae resulting in a reduced evaporation and contamination of the salt with gypsum and insoluble organic materials.

Optimal production of solar salt; both in terms of quality and quantity, requires a well-established balance between the primary and secondary producers, with brine shrimp Artemia grazing on phytoplankton constituting the major interaction. In this paper, we discuss the beneficial role of Artemia in balancing the hydrobiological activity of the salt pond system and highlight some of the critical aspects essential to proper managment of Artemia, including selection and controlled introduction of the most suitable strain of Artemia.

Furthermore, the possibilities for establishing a vertically integrated aquaculture industry brough about by the opportunities for harvesting of Artemia cysts and biomas as valuable by-products of the solar salt operation will be discussed. Results of experiences gained in different projects around the world will be presented.

THE NATURAL OCCURRENCE OF ARTEMIA

The brine shrimp Artemia is a small crustacean which is widely distributed on the five continents in hypersaline biotopes including salt lakes (coastal or inland waters riche in chloride, sulphate or carbonate) and especially in coastal salinas (man-made and/or managed solar saltworks). Detailed reviews can be found in Persoone and Sorgeloos (1980) and Sorgeloos et al. (1986). The very specific and large range of ecological characteristics of these Artemia habitats have resulted in the evolution of many geographical strains. At present over 350 different geographical strains are known (Vanhaecke et al., 1987)

In saltworks Artemia is found in the evaporation ponds only at intermediate salinity levels from about 100 ppt, the upper tolerance level of predators, to about 200–250 ppt, when food becomes limiting, and the Artemia need more energy for osmoregulation or when the water becomes more toxic in ionic composition as result of selective crystallisation of slats (see schematic outline in Fig. 1). At high salinities, depending in the local strain as well as the hydrobilogical conditions in the ponds (e.g. water retention time, water depth, pond productivity) cysts of Artemia (see Fig. 2) are produced seasonally or year-round. They float, tend to be driven by the wind, and often accumulate on the shores of the evaporation ponds.

HARVESTING OF NATURAL ARTEMIA HABITATS

Recent developments in aquaculture production of fish and shrimp have resulted in increased demands for Artemia as a valuable source of live feed. The present world market of Artemia cysts for use in aquaculture is estimated at over 700 t/year. Although the large part of this cyst market is currently supplied by harvests from one single location, i.e. the Great Salt Lake, Utah, USA, there is a steadily-growing interest in the commercial harvesting of other Artemia biotopes which is brought about by local import restrictions and/or the increasing demand for Artemia products. The quality of the Artemia produced differs from strain to strain and from location to location as a result of genotypical and phenotypical variations (for reviews are Leger et al 1986, 1987a). It largely reflects are food conditions of the local habitat; adults as well as cysts may be contaminated with high levels of heavy metals, and/or may be deficient in fatty acids essential for marine predators; furthermore, particular strains in specific habitats may produce cysts with unusually low content, e.g. the «sulphate strain» in Chaplin Lake, Canada (Vanhaecke et al., 1983). In this regard it is imperative to determine the nutritional quality of the adult Artemia and/or cysts for specific aquaculture purposes prior to consider commercial use of natural Artemia biotopes.

Techniques for cyst/biomass harvesting and treatment are outlined by Sorgeloos et al. (1986). Maximum sustainable yields of cysts and biomass are influenced by the population dynamies of the local Artemia population. The recruitment rate of the population may be high in ponds where the dominant reproduction mode is ovoviviparity, and low in cyst-production ponds. In the low salinity ponds it may be influenced by the role cysts as inoculum, either after the winter or throughout the year. Furthermore, production by water birds needs also to be taken into consideration. The determination of maximal havesting rates is complicated by the heerogenous distribution of the Artemia, which makes accurate sampling and consequently precise population estimates very difficult (for more details, see Wear and Haslett, 1987 a,b). Natural recuitment can eventually be increased by introduction of a more productive strain. Fertilization of the Artemia ponds can also result in increased production potentials.

In most Artemia habitats population densities are very low as a result of food limitation due to low nutrient contents of the intake waters. Some solar saltworks, especially those located in highly eutrophicated areas have, however, a very high productivity, e.g. Leslie saltworks in the San Francisco Bay, California, USA, and the solar saltworks along the Bohai Bay in P.R. China. In the latter area harvesting of cysts and especially biomass, used in local hatcheries and grow-out of white shrimps, has become a considerable industry employing several hundreds of people (Tackaert and Sorgeloos, 1992).

BENEFICIAL ROLE OF ARTEMIA IN SOLAR SALTWORKS

Since early times, man has developed systems to concentrate seawater and to harvest sodium chloride as a basic need for his nutrition and health. Over the centuries hundreds and thousands of hectares of salt pans have been constructed, all over the world, in tropical and sub-tropical belts, for socalled solar salt making. The annual production presently amounts to about 200 Mt/year. Less than 10% is used for human consumption, the bulk being consumed by chemical industries (e.g. the chlorine-alkali industries). Seawater contains salts of almost every chemical element including gold in at least trace amounts. Solar salt is normally produced by pumping seawater from one evaporation pond into another, allowing carbonates and gypsum to precipitate, and finally draining NaCl-saturated brine or «pickel» (just before the so-called «salting points» is reached) into crystallizer ponds where sodium chloride precipitates. Before all the NaCl has crystallized out, the mother liquor, now called bittern, has to be drained off to reduce contamination of the sodium chloride with bromides and other salts that begin to precipitate at these elevated salinities. The technique of solar salt production thus involves fractional crystallization of the salts in different ponds to obtain sodium chloride in the purest form possible e.g. up to 99,7% on a dry-weight basis.

Fig. 1. Schematic diagram of solar salt operation with natural occurrence of Artemia (from Sorgeloos et al., 1986).

Fig. 2. Schematic diagram of Artemia life cycle (from Sorgeloos et al., 1986).

The hydrobilogical activity in a solar-salt operation largely determines the quality and quantity of salt produced (Davis, 1978, 1980; Sorgeloos, 1983). In many sites the natural conditions ensure a maximal salt production (e.g. in France, Brazil and South Africa); in other locations, however, proper biological management is needed (e.g. in P.R. China, India, Italy, Autralia, Bahamas and Venezuela). Algal blooms, induced by natural availability of organic and inorganic nutrients, are generally beneficial since they ensure increased solar heat absorption resulting in faster evaporation and increased yields of salt. However, if they are not metabolized in time algal excretion and decomposition products, such as dissolved carbohydrates, act as chemical traps and consequently prevent early precipitation of gypsum which will contaminatate the sodium chloride in the crystallizers and reduces salt quality. Furthermore, such organic impurities as algal agglomerations, which turn black on oxidation, may contaminate the salt and reduce the size of the crystals and hence the salt quality. In the worst situations, high water viscosities may completely inhibit salt crystal formation and precipation. The presence of the brine shrimp Artemia in sufficient numbers is essential not only for controlling algal blooms (Davis, 1980), but also for providing essential nutrients from Artemia metabolites and/or decaying animals as suitable substractes for the development of Halobacterium in the crystallisation ponds (Jones et al., 1981). High concentrations of red halophilic bacteria promote heat absorption, thereby accelerating evaporation, and reduce concentrations of dissolved organics. Lower viscosity levels promote the formation of larger salt crystals, and thereby improve salt quality (Sorgeloos, 1983; Haxby and Tackaert, 1987). In many salt operations natural recruitment of Artemia from cysts dispersed by wind and water birds assures the presence and development of sufficient numbers of brine shrimp for optimal salt operation. In some situations, however, the salt producer should not rely on this opportunistic dispersion of Artemia. In saltworks with short waterretention times in their evaporation ponds, a rapid dilution may was away the Artemia population; a hurricane or season of exceptionally heavy rainfall may eliminate or so reduce the lcoal population that it cannot effectively cope with the algae blooms. Some saltworks may be completely isolated from natural sources of Artemia dispersion. In such cases salt producers should optimize the hydrobiological activity in the evaporation ponds through a controlled introduction of brine shrimp. Situations have also been observed where the local Artemia population has a poor productivity and remains too small to control the algae and ensure an optimal hydrobiological activity for the salt production. The introduction of a foreign strain, better adapted to the prevailing conditions or with better production characteristics, may improve conditions for production of high quality salt. It is not possible to formulate a general strategy with regard to Artemia introductions in solar-salt operations. Bach situation needs to be analyzed for specific requirements, with regard to selection of a suitable Artemia strain. The quality and quantity of Artemia to be introduced must be determined in consideration of the water retention times in evaporation reservoirs, food concentrations, water temperatures, etc. (Sorgeloos et al., 1986).

Proper Artemia management should lead not only to improved salt production outputs but also provide opportunities for the harvesting of the valuable by-product Artemia, as cysts and biomass.

INTRODUCTION OF ARTEMIA

Although Artemia is clearly cosmopolitan, a closer look at the regional level reveals that its distribution is discontinuous. Artemia does not occur in every existing body of seawater. Brine shrimps cannot migrate from one saline biotope to another via the sea, because they lack anatomical defences against predation by such carnivorous aquatic organisms as larger crustaceans and fish. The Artemia found in several saltworks have probably been accidentally introduced by man. Following and old custom, some slat farmers seeded new saltpans with salt, often containing Artemia cysts, from and operational saltwork. All Artemia populations in Australia were probably originally introduced by man and now compete, at least in low salinity ponds, with the endemic brine shrimp Par-artemia spp . (Geddes and Williams, 1987). The absence of a migration route of water birds probably explains why along the northeast coast of Brazil the very large salinas (several 10,000 ha in total area) contained no brine shrimp until Artemia franciscana was introduced in 1977 by man in just one saltern in Macau. A few years later it had already been dispersed by local water fowl from Macau to most of the saltworks of north-east Brazil, over a distance of more than 1,000 km (Camara and De Castro, 1983; Canara and De Medeiros Rocha, 1987).

Controlled introduction of Artemia by man into suitable biotopes not only provides interesting opportunities for aquaculture production but is also an interesting tool to balance the hydrobiological activity of those salt farms where Artemia is absent or too few to effectively cope with algal blooms. However, much caution is needed id one is to preserve the genetic diversity of indigenous brine shrimp populations, especially on the Australian continent, where several endemic species might be endangered by the presence of Artemia (see Geddes, 1980, 1981; Geedes and Williams, 1987). On other contients, detailed ecological analyses as well as collection and storage of viable cysts should precede any such new introductions.

Commercial considerations might eventually justify new Artemia introductions in solar salt operations where the salt production, quality and quantity, may be impaired by the absence or poor performance of local strains of Artemia (e.g. in India, Italy, Venezuela, Bahamas). Various so-called natural or indigenous Artemia populations may be illadapted to their environment because their local habitat has been modified by man in order to accommodate or improve salt production, resulting in new (sub-optimal) ecological conditions, e.g. in the deep Lago Salpi near Margherita di Savoia in Italy, which was converted into shallow evaporation ponds in which water temperatures in the summer rise above 30°C. lethal temperatures for the local A. parthenogenetica strain (Bargozzi and Trotta, pers, commun., 1980; Vanhaecke et al., 1984). Other examples are N. African Artemia populations of local commercial solar saltworks, which used to inhabit highly seasonal biotopes that filled up during winter precipitation period and dried up during the summer. Originally adapted to maximize population growth at relatively low temperatures, they do not readily tolerate the high summer temperatures to which they are now exposed in the salinas. A critical aspect regarding Artemia introduction is the selection of the strain to be inoculated. An accidental introduction of A, parthenogenetica from P.R. China into the solar salt operation on Great Inagua, Bahamas, resulted in significant reduction in salt quality and output (Morton Salt Cie, pers. commun, 1983). However, production returned to normal after the introduction of A. franciscana, which had previously been shown to control algal blooms under the local climate conditions (E. Haxby, pers. commun., 1984). Serious problems resulting in sub-optimal conditions for solar salt production may also arise when natural re-colonization of the salt ponds after the winter season is retarded due to particular cimatological conditions. This is the case in the solar saltworks of the Bohai Bay (P.R. China). These solar saltworks are fed highly entrophicated waters causing an excessive accumulation of organic matter detrimental to slat production (Davis, 1991). Despite the abundant availability of food under the form of unicellular algae, Artemia densities in these salt ponds remain very limited especially during spring and are unable to remove sufficient amounts of organic matter. Overwintering cysts to repopulate the biotope during spring only hatch in the low salinity ponds due to absence of rain during this period . As a result, rapid colonization of the entire saltwork is prevented, because the high salinity ponds become populated with Artemia only when brine together with animals flow from the low salinity ponds to the downstream ponds. Repopulation of the biotope is furthermore exacerbated by the limited productivity of the local parthenogenetic strain at the lower temperature regimes prevailing in the ponds during spring as well as the poor resistance of this strain to high salinity (Tackaert and Sorgeloos, 1991.). A recent inoculation trial, using Artemia franciscana from San Francisco Bay, USA, a strain selected for the its high productivity at relatively low temperatures and good resistance to high salinities (Vanhaecke and Sorgeloos, 1988) in a local experimental salt-works largely out-competed the parthenogenetic stain confirming its better suitability for the Chinese saltworks. Although not yet scientifically verified, better salt quality and higher yields of Artemia biomass were also reported in the Artemia franciscana inoculated salt ponds.

A new Artemia should be introduced only when one can be reasonably sure of its success, and certainly not before enough viable cyst material of the locally occuring stain has been collected to safeguard the conservation of this Artemia genepool. In accordance with a resolution adopted at the Second International Artemia Symposium, ((…all possible measures (should) be taken to ensure that the genetic resources of natural Artemia populations are conserved)). Such measures include the establishment of gene banks (cysts), close monitoring of inoculation policies and, where possible, the use of indigenous Artemia for inoculating Artemia-free ponds (Beardmore, 1987). Selection of the inoculated strain should be based on the available data on temperature and salinity tolerances (Vanhaecke et al., 1984); Vanhaecke and Sorgeloos, 1988), growth and production, reproductive characteristics, etc. Whenever possible, culture tests with various Artemia strains should be performed in simulated conditions, using the untreated waters of the habitat as culture medium. Competition between parthenogenetic and bisexual strains might favour the first when dealing with European bisexuals (A. tunisiana), although co-existence has been reported (Amat, 1983) with dominance of the parthenogenetic strain in the summer months. On the other hand we can confirm that A. franciscana strain s always outcompete any other Artemia strain (Browne, 1980). Strain selection might also be restricted by the intended application of the produced Artemia in local aquaculture, e.g. and Artemia strain producing small cysts might be selected for use in sea-bass farming. Such introductions generally result in the permanent establishment of an Artemia population; introduction of an unsuitable strain cannot be readily rectified. Furthermore, adaptation of a newly inoculated strain may result in phenotypical and genotypical variations in the pre-existing stocks, eventually yielding a new Artemia genotype (Vanhaecke and Sorgeloos, 1988).

CONCLUSION

Now that it has been shown that salt making and Artemia production go hand in hand, one can envisage attractive joint ventures for shrimp and fish aquaculture operations to integrate with solar saltworks in some of the many thousands of hectares of salinas in the tropical-subtropical areas, often in climates that favour crustacean or fish farming. Furthermore, it can lead to an extra source of income for families in many developing countries (Sahavacharin, 1981).

ACKNOWLEDGEMENTS

This study has been supported by the Belgian National Science Foundation (NFWO-FKFO), the Belgian Administration for Development Cooperation and the Belgian Ministry of Science Policy.

REFERENCES

AMAT, T., 1983. Zygogenetic and parthenogenetic Artemia in Cadiz sea-side salterns. Mar. Ecol. Prog. Ser., 13(2–3): 291–293.

BEARDMORE, J.A., 1987. Concluding remarks. In: P. Sorgeloos, D.A. Bengtson, W. Decleir and B. Jaspers (Editors), Artemia Research and its applications. Vol. 1. Universal Press, Watteren, Belgium, pp. 345–346.

BROWNE, R.A., 1980. Competition experiments between parthenogenetic and sexual strains of the brine shrimp, Artemia salina. Ecology, 61(3):471–774.

CAMARA, M.R. and DE CASTRO, E.V., 1983. Artemia salina L. (Anostraca): Uma opeao para aquicultura do Nordeste do Brasil. Revta Bras. Zool., S. Paulo, 1(3):145–147.

CAMARA, M.R. and DE MEDEIROS ROCHA, R., 1987. Artemia culture in Brasil: an overview. In: P. Sorgeloos, D.A. Bengtson, W. Decleir and E. Jaspers (Editors), Artemia Research and its Applications. Vol. 3. Universa Press, Wetteren, Belgium, pp. 195–199.

DAVIS, J.S., 1978. Biological communities of a nutrient enriched salina. Aquatic Botany, 4:23–42

DAVIS, J.S., 1980. Experiences with Artemia at solar salt-works. In: Persoone, P. Sorgeloos, O. Roels and B: Jaspers (Editors). The Brine Shrimp Artemia. Vol. 3. Ecology, Culturing, Use in Aquaculture. Universal Press, Watteren, Belgium, pp. 51–55.

DAVIS, J.S., 1991. Biological management for the nutrient-rich Chinese solar saltworks In: L. Cheng (Editor), Proceedings of Internationl Symposium on Biotechnology of Salt-ponds, Salt Research Institute, Tanggu, Tianjin, PR China, 128–132 pp.

GEDDES, M.C., 1980. The brine shrimp Artemia and Parartemia in Australia. In: G. Persoone, P. Sorgeloos, O. Roels and E. Jaspers (Editors). The brine Shrimp Artemia. Vol. 3. Ecology Culturing, Use in Aquaculture. Universa Press, Wetteren, Belgium, pp. 57–65.

GEDDES, M.C., 1981. The brine shrimps Artemia and Parartemia. Comparative physiology and distribution in Australia. Hydrobiologia, 81:169–222.

GEDDES, M.C. and WILLIAMS, W.D., 1987. Comments on Artemia introductions and the need for cosnervation. In: P. Sorgeloos, D.A. Bengtson, W. Decleir and E. Jaspers (Editors). Artemia Research and Its Applications. Vol. 3. Universal Press, Wetteren, Belgium, pp. 19–26.

HAXBY, R.B. and TACKAERT W., 1987. Workshop report: Role of Artemia in solar salt operations. In: P. Sorgeloos, D.A. Bengtson, W. Decleir and E. Jaspers (Editors). Artemia Research and Its Applications. Vol. 3. Universa Press, Wetteren, Belgium, pp. 291–293.

JONES, A.G., EWING, C.M. and MELVIN, M.V., 1981. Biotechnology of solar saltfields. Hydrobiologia, 82: 391–406.

LÉGER, P.H., BENGTSON, D.A., SIMPSON, K.L. and SORGELOOS, P., 1986. The use and nutritional value of Artemia as food source, Oceanogr. Mar. Biol. Ann. Rev., 24:521–623.

LÉGER, P.H., BENGTSON, D.A., SORGELOOS, P., SIMPSON, K.L. and BECK, A.D., 1987a. The nutritional value of Artemia, a review, In: P. Sorgeloos, D.A. Bengtson, W. Decleir and E. Jaspers, (Editors). Artemia Research and Its Applications. Vol. 3. Unitversa Press, Wetteren, Belgium, pp. 357–372.

PERSOONE, G. and SORGELOOS, P., 1980. General aspects of the ecology and biogeography of Artemia, In: G. Persoone, P. Sorgeloos, O. Roels, and E. Jaspers (Editors). The Brine Shrimp Artemia, Vol. 3. Ecology, culturing, use in aquaculture. Universa Press, Wetteren, Belgium, pp. 3– 24.

SAHAVACHARIN, S., 1981. Ways to convert salt farm to Artemia farm (in Thai, with English abstract). Thai Fisheries Gazette, 34(5): 467–480.

SORGELOOS, P., 1983. Brine Shrimp Artemia in coastal salt-works: inexpensive source of food for vertically integrated aquaculture. Aquaculture Magazine, 9:25–27.

SORGELOOS, P., LAVENS, P., LÉGER, PH., TACKAERT, W. and VERSICHELE, D., 1986. Manual for the Culture and Use of Brine Shrimp Artemia in Aquaculture. Artemia Reference Center, State University of Ghent, Belgium, 319 pp.

TACKAERT , W. and SORGELOOS, P., 1991. Biological management to improve Artemia and salt productions at Tank Gu Salt-works in the P.R. China In: L. Cheng (Editor), Proceedings of International Symposium on Biotechnology of Salt-ponds, Salt Research Institute, Tanggu, Tianjin, PR China, pp. 78–83.

TACKAERT, W. and SORGELOOS, P., 1992. Salt, Artemia and shrimp. Integrated production in the Peoples' Republic of China. The Tang Gu Saltworks World Aquaculture, in press.

VANHAECKE, P., LAVENS, P. and SORGELOOS, P., 1983. International Study on Artemia XVII Energy consumption in cysts and early larval stages of various geographical stains of Artemia. Annls. Soc. r. zool. Belg. 113(2): 155–164.

VANHAECKE, P., SIDDAL, S.E. and SORGELOOS, P., 1984. International Study en Artemia. XXXXII combined effects of temperature and salinity on the survival of Artemia of various geographical origin. J. Exp. Mar. Bio. Ecol., 80(3): 259–275.

VANHAECKE, P. and SORGELOOS, P., 1988. International Study on Artemia. The effect of temperature on cyst hatching, larval survival and biomass production of different geographical strains of Artemia. Submitted for Publication.

VANHAECKE, P., TACKAERT, W. and SORGELOOS, P., 1987. The biography of Artemia: an updated review. In: P. Sorgeloos, D.A. Bengtson, W. Decleir and E. Jaspers (Editors), Artemia Research and Its Applications, Vol. 1. Universa press. Wetteren, Belgium, pp. 129–159.

WEAR, R.G. and HASLETT, S.J., 1987a. Studies on the biology and ecology of Artemia from Lake Grasmere, New Zealand. In: P. Sorgeloos, D.A. Bengtson, W. Decleir and E. Jaspers (Editors), Artemia Research and its Applications. Vol. 3. Universa Press, Wetteren, Belgium, pp. 101–126.

WEAR, R.G. AND HASLETT, S.J., 1987B: A minimal strategy for assessing Artemia biomass harvestable from production salinas. In: P. Sorgeloos, D.A. Bengtson, W. Decleir and E. Jaspers (Editors), Artemia Research and its Applications. Vol. 3. Universa Press, Welleren, Belgium, pp. 217–220.