Innate immunity of fish (overview).

The integumental defenses provide a physical and chemical barrier to the attachment and penetration of microbes. Besides the entrapping and sloughing of microbes in the mucus, the latter contains many antibacterial substances including anti-bacterial peptides, lysozyme, lectins and proteases. The gastro-intestinal tract is a hostile environment of acids, bile salts and enzymes able to inactivate and digest many viruses and bacteria. In most cases the integumental defenses are sufficient to protect against even quite virulent organisms which often only produce disease when the integument has been physically damaged. If a microbe gains access to the tissues of the fish, it is met with an array of soluble and cellular defenses. The complement system, present in the blood plasma, plays a central role in recognising bacteria and its activated products may lyse the bacterial cells, initiate inflammation, induce the influx of phagocytes and enhance their phagocytic activity. Complement can be activated directly by bacterial products and constituents and also indirectly by other factors, principally C-reactive protein and lectins, which can also bind to the bacterial surface. Plasma also contains a number of factors which inhibit bacterial growth(e.g. transferrin and anti-proteases) or which are bactericidal e.g. lysozyme. Following the infection of fish with virus pathogens, infected cells produce interferon. This induces antiviral defenses in neighbouring cells which are then protected from becoming infected. Anti-viral cytotoxic cells are able to lyse virally infected cells and thus reduce the rate of multiplication of virus within them. Innate defenses thus provide a pre-existing and fast-acting system of protection which is non-specific and relatively temperature-independent and thus has several advantages over the slow-acting and temperature-dependent specific immune responses.

Innate host defense mechanisms of fish against viruses and bacteria

Essential fatty acid (EFA) requirements vary qualitatively and quantitatively with both species and during ontogeny of fish, with early developmental stages and broodstock being critical periods. Environment and/or trophic level are major factors, with freshwater/diadromous species generally requiring C18 polyunsaturated fatty acids (PUFA) whereas marine fish have a strict requirement for long-chain PUFA, eicosapentaenoic, docosahexaenoic and arachidonic acids. Other than marine fish larvae, defining precise quantitative or semi-quantitative EFA requirements in fish have received less attention in recent years. However, the changes to feed formulations being forced upon the aquaculture industry by the pressing need for sustainable development, namely the replacement of marine fish meal and oils with plant-derived products, have reintroduced EFA into the research agenda. It is particularly important to note that the physiological requirements of the fish to prevent deficiency pathologies and produce optimal growth may not parallel the requirements for maintaining nutritional quality. For instance, salmonids can be successfully cultured on vegetable oils devoid of long-chain n-3 PUFA but not without potentially compromising their health benefits to the human consumer. Solving this problem will require detailed knowledge of the biochemical and molecular basis of EFA requirements and metabolism.

Fatty acid requirements in ontogeny of marine and freshwater fish

The immune system of fish is very similar to vertebrates, although there are some important dif - ferences. Fish are free-living organisms from the embryonic stage of life in their aquatic environment. They have mechanisms to protect themselves from a wide variety of microorganisms. Consequently, fish rely on their innate immune system for an extended period of time, beginning at the early stages of embryogenesis. The components of the innate immune response are divided into physical, cellular and humoral factors and include humoral and cellular receptor molecules that are soluble in plasma and other body fluids. The lymphoid organs found in fish include the thymus, spleen and kidney. Immunoglobulins are the principal components of the immune response against pathogenic organisms. Immunomodulatory products, including nucleotides, glucans and probiotics, are increasingly used in aquaculture production. The use of these products reduces the need for therapeutic treatments, enhances the effects of vaccines and, in turn, improves the indicators of production. The aim of this review is to provide a review of the immune system in fish, including the ontogeny, mechanisms of unspecific and acquired immunity and the action of some immunomodulators.

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Innate and adaptive immunity in teleost fish: a review.

The innate immune response of finfish--a review of current knowledge.

Can Atlantic salmon (Salmo salar) grow on diets devoid of fish meal

Assessment of lysine requirement for maximal protein accretion in Atlantic salmon using plant protein diets

Methionine intake affect hepatic sulphur metabolism in Atlantic salmon, Salmo salar

Effect of stachyose, raffinose and soya-saponins supplementation on nutrient digestibility, digestive enzymes, gut morphology and growth performance in Atlantic salmon (Salmo salar, L)

Triplicate groups of triploid and diploid Atlantic salmon were fed diets with a low (LP, total P: 71 g kg−1), medium (MP, total P: 94 g kg−1) or high (HP, total P: 163 g kg−1) phosphorous (P) level from first feeding (018 g) to transfer to sea water (~50 g, duration: 203 days) and subsequently fed a commercial diet in sea water for 426 days (~3 kg) This study examined the short- and long-term effects of dietary P on freshwater performance (mortality, growth), vertebral deformities (radiology), bone cell activity (ALP and TRACP enzyme activity in vertebrae and scales, and fgf23, bgp and igf-I relative gene expression in vertebrae), bone mineralization (ash content) and some parameters related to fish condition (heart and liver size) Irrespective of ploidy, at seawater transfer, fish fed the MP diet had significantly highest length and weight and those fed the LP diet significantly lowest length and weight, while those fed the HP diet had intermediate lengths and weights Increased dietary phosphorus reduced deformities in both ploidies at seawater transfer; however, triploids fed the LP and MP diets had more deformities than diploids fed the respective diets, while there was no ploidy effect observed for fish fed the HP diet The vertebral bone ash content at seawater transfer was significantly higher in diploids than in triploids when fed the MP diet only Alkaline phosphatase (ALP) and tartrate-resistant acid phosphatase (TRACP) enzyme activities and relative gene expression of bone hormones involved in metabolism of plasma phosphate (fgf23) and bone growth (bgp) were not affected by ploidy at seawater transfer, but by dietary P level; LP increased ALP activity and reduced TRACP activity and fgf23 and bgp expression levels in vertebral bone In scales, LP increased both ALP and TRACP activity At the termination of the seawater period, the group-wise pattern in occurrence of vertebral deformities was the same as at seawater transfer The present results on mortality, growth, bone mineralization and development of skeletal deformities all demonstrate that triploids have a higher P requirement than diploids in fresh water This study shows that an optimalization of P nutrition for triploid Atlantic salmon can improve health and welfare and reduce down-grading of triploid salmon

Adel El-Mowafi

Papers

Can Atlantic salmon (Salmo salar) grow on diets devoid of fish meal

Assessment of lysine requirement for maximal protein accretion in Atlantic salmon using plant protein diets

Methionine intake affect hepatic sulphur metabolism in Atlantic salmon, Salmo salar

Effect of stachyose, raffinose and soya-saponins supplementation on nutrient digestibility, digestive enzymes, gut morphology and growth performance in Atlantic salmon (Salmo salar, L)

Increased dietary phosphorous prevents vertebral deformities in triploid Atlantic salmon (Salmo salar L.)