Patrick Sorgeloos

Probiotic Bacteria as Biological Control Agents in Aquaculture

SUMMARY There is an urgent need in aquaculture to develop microbial control strategies, since disease outbreaks are recognized as important constraints to aquaculture production and trade and since the development of antibiotic resistance has become a matter of growing concern. One of the alternatives to antimicrobials in disease control could be the use of probiotic bacteria as microbial control agents. This review describes the state of the art of probiotic research in the culture of fish, crustaceans, mollusks, and live food, with an evaluation of the results obtained so far. A new definition of probiotics, also applicable to aquatic environments, is proposed, and a detailed description is given of their possible modes of action, i.e., production of compounds that are inhibitory toward pathogens, competition with harmful microorganisms for nutrients and energy, competition with deleterious species for adhesion sites, enhancement of the immune response of the animal, improvement of water quality, and interaction with phytoplankton. A rationale is proposed for the multistep and multidisciplinary process required for the development of effective and safe probiotics for commercial application in aquaculture. Finally, directions for further research are discussed.

Use of the brine shrimp, Artemia spp., in marine fish larviculture.

Since no artificial feed formulation is yet available to completely substitute for Artemia, feeding live prey to young fish larvae still remains essential in commercial hatchery operations. The nutritional quality of commercially available Artemia strains being relatively poor in Ž. Ž

Alternatives to antibiotics for the control of bacterial disease in aquaculture

The wide and frequent use of antibiotics in aquaculture has resulted in the development and spread of antibiotic resistance. Because of the health risks associated with the use of antibiotics in animal production, there is a growing awareness that antibiotics should be used with more care. This is reflected in the recent implementation of more strict regulations on the prophylactic use of antibiotics and the presence of antibiotic residues in aquaculture products. For a sustainable further development of the aquaculture industry, novel strategies to control bacterial infections are needed. This review evaluates several alternative biocontrol measures that have emerged recently. Most of these methods are still in research phase; few have been tested in real aquaculture settings. It is important to further develop different strategies that could be combined or used in rotation in order to maximise the chance of successfully protecting the animals and to prevent resistance development.

Artemia : basic and applied biology

Preface. Editorial Note on Terminology. Acknowledgments. I. Artemia Morphology and Structure. II. Reproductive Biology of Artemia. III. Physiological and Biochemical Aspects of Artemia Ecology. IV. Zoogeography. V. Evolution and Speciation. VI. Applications of Artemia. Index.

Review on the dietary effects of phospholipids in fish and crustacean larviculture.

A beneficial effect of dietary phospholipid (PL) supplementation in purified diets in terms of survival, growth, resistance to stress tests, and occurrence of deformities has been demonstrated in larval and juvenile stages of various species of fish and crustaceans. The exact determination of PL requirements in larvae is complicated due to the difficulty to bio-encapsulate PL in live prey. Furthermore, the great variety in purity and composition of the PL sources, and the experimental conditions (such as diet formulation and extent of co/prefeeding with live food) makes it difficult to compare requirements determined with artificial diets. Larval stages are extremely sensitive to a dietary PL deficiency and require higher levels of dietary PL than juveniles. For most of the fish and crustacean species examined, the estimated PL requirement of larvae are in the range of 1–3% phosphatidylcholine + phosphatidylinositol (PC + PI) of diet dry weight. The absence of a PL requirement in the freshwater prawn Macrobrachium rosenbergii exemplifies the important species differences. The few studies evaluating single PL demonstrate that PC and PI are the most efficient in most species. The presence of an unsaturated fatty acid in sn−2 position of the PL molecule seems to be essential for the functionality of PL. Some studies in crustaceans reported a relation between PL requirements and the protein source in the diet. Various hypotheses have been formulated to explain the effect of PL. The PL effect is not related to the provision of choline, inositol or essential fatty acids (EFA). However, PL may be superior to neutral lipids for larvae as a source of EFA and energy due to their better digestibility. PL may improve the performance of the diet by improving the water stability of food particles, or by their action as antioxidant or feed attractant. The effect of dietary PL appears not to be explained by their emulsifying ability. However, there are proofs that dietary PL interfere with lipid transport, especially cholesterol transport in crustaceans, and with retention of fatty acids provided by dietary triacylglycerol. Although the origin of the requirement is still unclear, dietary PL supplementation has potential importance for the formulation of practical larval diets.

The history, present status and prospects of the availability of Artemia cysts for aquaculture.

This paper provides an overview of the history of Artemia cyst provision worldwide since the 1950s. It allows a better assessment of the current situation, characterized by poor yields from the main harvest site, the Great Salt Lake in Utah, USA, and to make prognoses about future supplies and demands.

Effect of dietary non-protein energy levels on condition and oxidative status of Senegalese sole (Solea senegalensis) juveniles

The effects of dietary non-protein energy levels on growth, oxidative status and condition were studied in juveniles of Senegalese sole (Solea senegalensis). Four isonitrogenous diets with four energy levels were used: A-low (11% lipid, raw carbohydrate); B-intermediate (11% lipid, digestible carbohydrate); C-intermediate (21% lipid, raw carbohydrate); and D-high (21% lipid, digestible carbohydrate). Survival, relative growth rate (RGR) and feed conversion rate were not significantly affected by the dietary treatments. The fatty acid composition of the fish muscle varied little among the treatments, but trans 18:2n - 6, total n - 6 and EPA/DHA ratio, tended to be higher in fish fed diets with low lipid level. Cellular energy allocation (CEA) results (indicative of metabolic status and net energy budgets) showed significant differences in liver, but not in muscle samples. Livers of fish fed diet C contained the lowest carbohydrate, protein and CEA values, but the highest cellular energy consumption. Fish fed diet A had the highest CEA for growth, followed by fish fed diets B and D and then diet C. The liver and muscle peroxidation and antioxidant activity were measured by thiobarbituric acid reactive substances (TBARS) test and the enzymatic activities levels of catalase (CAT) and superoxide dismutase (SOD). TBARS values were higher for fish fed diets with high lipid content. However, no clear relation was found between HUFA level and TBARS value. The activity levels of the antioxidant enzymes CAT and SOD were higher in livers of fish fed diets with a high lipid level. Furthermore, CAT and SOD activity and TBARS values were influenced by the type of dietary starch in the diet. Higher oxidation rates were observed in fish fed diets containing raw carbohydrate. These data suggest that lipid and carbohydrate energy sources affect the oxidative status of Senegalese sole. Diets containing low levels of lipid and digestible starch reduce the susceptibility of the fish to oxidation and may enhance growth rate

International study on Artemia. 19. Hatching data for ten commercial sources of brine shrimp cysts and re-evaluation of the "hatching efficiency" concept.

Abstract A comparative hatching study has been carried out with Reference Artemia Cysts as well as cysts from Argentina, Australia, Brazil, Canada, France, Italy, the Peoples Republic of China, the Philippines and the U.S.A. Hatching rate, percentage and efficiency vary considerably from one cyst source to another. These hatching criteria are, however, not strainspecific since significant variation is found among cyst batches from the same geographical origin. The limitations of the “hatching efficiency” concept are discussed and a new criterion “hatching output”, i.e. the biomass of nauplii expressed in mg dry weight produced per gram cyst product, is proposed for evaluation of the hatching quality of Artemia cyst brands. The hatching quality of Reference Cysts and cysts from Canada and Argentina can be significantly improved by incubation of the cysts at low salinity. For almost all commercial sources the use of decapsulated cysts results in a significant increase of the hatching output.

Advancement of rotifer culture and manipulation techniques in Europe

Abstract Since no artificial feed formulation for first feeding of marine larval fish has been developed yet, live prey feeding remains essential in commercial marine hatchery operations. Because cultured rotifers are relatively poor in eicosapentaenoic acid (EPA: 20:5n-3) and docosahexaenoic acid (DHA: 22:6n-3), it is essential and therefore common practice to enrich these live prey with emulsions of marine oils. The short-term exposure to oil emulsions results in lipid-encapsulated rotifers with high EPA and DHA levels. However, these rotifers are prone to fast losses of their gut content and show a distortion in their protein/lipid balance. Rather than submerging rotifers in oil emulsions, it is often preferred to use formulated culture diets when medium to low enrichment values are needed in live prey. The use of these diets contributes not only to the filling of the gut of the rotifers with nutrients, it generally creates a more stable entire body composition which is important especially when rotifers are not consumed immediately by the larvae. New culture techniques for rotifers, such as closed recirculation systems, are offering new possibilities for continuous supplies of high quality rotifers at 10 times higher densities than in batch cultures. The production increase in these systems is explained by the better water quality obtained by the introduction of protein skimmers, ozone treatment, and biological filtration. Although disinfection of rotifers remains a bottleneck, it has been observed that rotifer populations cultured at high densities are not prone to higher bacterial infestation. Also, the problem of unexplained mortalities in batch cultures seems to be partly solved by the introduction of recirculation systems or by bacterial management (introduction of probionts), which allow more reliable rotifer production.

Proposal for a short-term toxicity test with Artemia nauplii.

Abstract Although standardization of toxicity tests on aquatic organisms is an urgent necessity, very little has yet been achieved for the marine environment. As a first step in this direction, a simple, inexpensive and reliable short-term routine test with Artemia larvae is proposed. This test is the result of an extensive study in our laboratory, taking into account the advantages and disadvantages of Artemia bioassays published by various authors. The major advantage of the brine shrimp as a test species is its continuous availability under the form of dry cysts which can be hatched very easily; this eliminates all biological, technological, and financial problems of stock recruitment and/or culturing. The acute test presented is based on the determination of the LC50-24 hr of instar II–III nauplii of a specific Artemia strain. Presently this test is the subject of an intercalibration exercise in North America; an analogous exercise is now in progress in the European Economic Community countries.