Innate immunity of fish (overview).

Current research status of fish immunostimulants

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A Toll-like receptor recognizes bacterial DNA

Unsustainable fishing practices have placed a heavy emphasis on aquaculture to meet the global shortfalls in the supply of fish and seafood, which are commonly accepted as the primary source of health-promoting essential omega-3 (n-3 highly unsaturated fatty acids). However, dietary fish oil is required for the production of omega-3-rich farmed fish and this commodity, in a vicious circle, is at present derived solely from wild fisheries. Decreasing global availability coupled with the highly variable price of this resource has forced the aquaculture industry to investigate the possibilities of alternative dietary lipid sources. This review attempts to compile all principal information available regarding the effects of fish oil replacement for the diets of farmed finfish, analysing the findings using a comparative approach among different cultured fish species. The review initially focuses on the present situation with regard to the production, availability and main nutritional characteristics of fish oil and the principal alternative lipid sources (such as vegetable oils and animal fats). Following this, the effects of fish oil replacement in finfish nutrition on feed quality, fish performance, feed efficiency, fish lipid metabolism, final eating quality and related economic aspects are presented and discussed.

Fish oil replacement in finfish nutrition

Probiotics and immunity: a fish perspective.

A prebiotic is a non-digestible food ingredient that beneficially affects the host by selectively stimulating the growth and/or the activity of one or a limited number of bacteria in the colon. Despite the potential benefits to health and performance as noted in various terrestrial animals, the use of prebiotics in the farming of fish and shellfish has been less investigated. The studies of prebiotics in fish and shellfish have investigated the following parameters: effect on growth, feed conversion, gut microbiota, cell damage/morphology, resistance against pathogenic bacteria and innate immune parameters such as alternative complement activity (ACH50), lysozyme activity, natural haemagglutination activity, respiratory burst, superoxide dismutase activity and phagocytic activity. This review discusses the results from these studies and the methods used. If the use of prebiotics leads to health responses becoming more clearly manifested in fish and shellfish, then prebiotics might have the potential to increase the efficiency and sustainability of aquaculture production. However, large gaps of knowledge exist. To fully conclude on the effects of adding prebiotics in fish diets, more research efforts are needed to provide the aquaculture industry, the scientific community, the regulatory bodies and the general public with the necessary information and tools.

Prebiotics in aquaculture: a review

The use of immunostimulants in fish larval aquaculture.

An efficient clearance and degradation system may be needed during microbial invasion which otherwise would lead to severe inflammation and eventually death. Non-specific defence mechanisms in fish play an important role at all stages in infection. The non-specific humoral defence including proteases, lysins and agglutinins, for example, in mucosal secretion is the first line of defence, whereas mucosal lining cells function as the second barrier against invasion. Blood cells, especially granulocytes and monocytes, may destroy microbes present in the circulation and may function as the third line of defence. Finally, endocytically active cells such as endothelial cells, macrophages and granulocytes in organs and tissues may take up and degrade microbes or microbial products. The endocytic and degradation processes strongly depend on the effectiveness of the reticuloendothelial system which consists of endothelial cells and macrophages that line small blood vessels (e.g. sinusoids and ellipsoids). Potentiation of non-specific defence mechanisms may occur during microbial invasion, leading to more efficient clearance and destruction of pathogens or other harmful substances. In microbial invasion, an inflammatory response such as elevated production of antimicrobial substances is often encountered. Central cells in the production of antimicrobial substances are macrophages and granulocytes, and microbial products in inflammation may alter the cells function to a more activated state in vivo. Activated cells may enhance their antimicrobial capacity and efficiency by producing higher amounts and more active antimicrobial agents. This review concerns the non-specific defence system and gives an introduction to some of the known non-specific humoral substances and their induction/suppression, and provides a more extensive introduction to cytokine research and immunomodulation. Cellular aspects of non-specific defence, including macrophages and their products, are discussed in the light of their function in the reticuloendothelial system in fish.

Roy A. Dalmo

Papers

Prebiotics in aquaculture: a review

The use of immunostimulants in fish larval aquaculture.

Non-specific defence mechanisms in fish, with particular reference to the reticuloendothelial system (RES)

Beta-glucans as conductors of immune symphonies.

Ontogeny of humoral immune parameters in fish.