Overview of Nutritional Strategies Affecting Health of Marine Fish

ABSTRACT

Proper nutrition plays a critical role in maintaining normal growth and health of cultured fish. A variety of nutritional strategies may influence fish health, including adjustment of specific nutrient levels in the diet, manipulation of nutritional condition through feeding regimens, and administration of non-nutrient immunostimulants in the diet. Research with several fishes, including some marine and diadro-mous species such as salmonids, has established that immunocompet-ence and disease resistance can be compromised by deficiencies of various nutrients, especially certain vitamins and minerals. Thus, adequate levels of these micronutrients must be supplied in prepared diets to support optimal growth and production efficiency of fish in aquacul-ture. In addition, dietary supplementation of some of these micronutri-ents in excess of minimum requirement levels has been shown to significantly enhance immune responses and disease resistance of various animals. Overfortification of such nutrients as vitamin C, vitamin E, and selenium have shown positive influences on immunity and disease resistance in some studies but no effects in other studies. Management practices that affect the nutritional condition of fish also may influence their health and ability to resist disease. Recent research with freshwater fish indicates certain feeding regimens, including moderate feed deprivation, alter a fish's resistance to disease. Such feeding regimens potentially may be applied to reduce losses of marine fish in aquacul-ture. Dietary supplementation of non-nutrient immunostimulatory compounds also has attracted considerable interest due to positive responses of several fish species in terms of non-specific immunity and disease resistance. Compounds such as −1,3-glucans which are derived from yeasts and fungi have been shown to change the activation level of different parts of the non-specific immune system, resulting in significantly reduced mortality after challenge with various pathogens. Some of these compounds have become commercially available in recent years, but their efficacy has been variable when administered in the diet. Specific examples concerning application of these various nutritional strategies in aquaculture are presented. Further advancements in these areas may allow nutritional modulation of the immune response to be used as an effective and relatively inexpensive alternative to chemical therapy in combating diseases of fish in aquaculture.

Key Words:

• Marine fish
• nutrition
• health
• immunomodulation