The innate immune system of fish is considered to be the first line of defence against a broad spectrum of pathogens and is more important for fish as compared with mammals. Lysozyme level or activity is an important index of innate immunity of fish and is ubiquitous in its distribution among living organisms. It is well documented that fish lysozyme possess lytic activity against both Gram-positive bacteria and Gram-negative bacteria. It is also known to be opsonic in nature and activates the complement system and phagocytes. It is present in mucus, lymphoid tissue, plasma and other body fluids of freshwater and marine fish. It is also expressed in a wide variety of tissues. Lysozyme activity has been shown to vary depending on the sex, age and size, season, water temperature, pH, toxicants, infections and degree of stressors. Here, we review our current understanding of different types of lysozyme and their expression and its role in fish innate immune system.

Lysozyme: an important defence molecule of fish innate immune system

Current research status of fish immunostimulants

Microalgae (including the cyanobacteria) are established commercial sources of high-value chemicals such as β-carotene, astaxanthin, docosahexaenoic acid, eicosahexaenoic acid, phycobilin pigments and algal extracts for use in cosmetics. Microalgae are also increasingly playing a role in cosmaceuticals, nutraceuticals and functional foods. In the last few years, there has been renewed interest in microalgae as commercial sources of these and other high-value compounds, driven in part by the attempts to develop commercially viable biofuels from microalgae. This paper briefly reviews the main existing and potential high-value products which can be derived from microalgae and considers their commercial development with a particular focus on the various aspects which need to be considered on the path to commercialisation, using the experience gained in the commercialisation of existing algae products. These considerations include the existing and potential market size and market characteristics of the product, competition by chemically synthesised products or by ‘natural’ compounds from other organisms such as fungi, bacteria, higher plants, etc., product quality requirements and assurance, and the legal and regulatory environment.

High-value products from microalgae—their development and commercialisation

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

During osteogenesis, osteoblasts lay down osteoid and transform into osteocytes embedded in mineralized bone matrix. Despite the fact that osteocytes are the most abundant cellular component of bone, little is known about the process of osteoblast-to-osteocyte transformation. What is known is that osteoblasts undergo a number of changes during this transformation, yet retain their connections to preosteoblasts and osteocytes. This review explores the osteoblast-to-osteocyte transformation during intramembranous ossification from both morphological and molecular perspectives. We investigate how these data support five schemes that describe how an osteoblast could become entrapped in the bone matrix (in mammals) and suggest one of the five scenarios that best fits as a model. Those osteoblasts on the bone surface that are destined for burial and destined to become osteocytes slow down matrix production compared to neighbouring osteoblasts, which continue to produce bone matrix. That is, cells that continue to produce matrix actively bury cells producing less or no new bone matrix (passive burial). We summarize which morphological and molecular changes could be used as characters (or markers) to follow the transformation process.

http://www.homepages.ucl.ac.uk/~ucgatma/Anat3048/PAPERS%20etc/Franz-Odenaal%20et%20al%202006.pdf

Buried alive: how osteoblasts become osteocytes.

There is an increasing drive to replace fish oil (FO) in finfish aquaculture diets with vegetable oils (VO), driven by the short supply of FO derived from wild fish stocks However, little is known of the consequences for fish health after such substitution The effect of dietary VO on hepatic gene expression, lipid composition and growth was determined in Atlantic salmon (Salmo salar), using a combination of cDNA microarray, lipid, and biochemical analysis FO was replaced with VO, added to diets as rapeseed (RO), soybean (SO) or linseed (LO) oils Dietary VO had no major effect on growth of the fish, but increased the whole fish protein contents and tended to decrease whole fish lipid content, thus increasing the protein:lipid ratio Expression levels of genes of the highly unsaturated fatty acid (HUFA) and cholesterol biosynthetic pathways were increased in all vegetable oil diets as was SREBP2, a master transcriptional regulator of these pathways Other genes whose expression was increased by feeding VO included those of NADPH generation, lipid transport, peroxisomal fatty acid oxidation, a marker of intracellular lipid accumulation, and protein and RNA processing Consistent with these results, HUFA biosynthesis, hepatic β-oxidation activity and enzymic NADPH production were changed by VO, and there was a trend for increased hepatic lipid in LO and SO diets Tissue cholesterol levels in VO fed fish were the same as animals fed FO, whereas fatty acid composition of the tissues largely reflected those of the diets and was marked by enrichment of 18 carbon fatty acids and reductions in 20 and 22 carbon HUFA This combined gene expression, compositional and metabolic study demonstrates that major lipid metabolic effects occur after replacing FO with VO in salmon diets These effects are most likely mediated by SREBP2, which responds to reductions in dietary cholesterol These changes are sufficient to maintain whole body cholesterol levels but not HUFA levels

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Functional genomics reveals increases in cholesterol biosynthetic genes and highly unsaturated fatty acid biosynthesis after dietary substitution of fish oil with vegetable oils in Atlantic salmon (Salmo salar)

Alex Obach

Papers

Functional genomics reveals increases in cholesterol biosynthetic genes and highly unsaturated fatty acid biosynthesis after dietary substitution of fish oil with vegetable oils in Atlantic salmon (Salmo salar)

Immunomodulation by dietary vitamin C and glucan in rainbow trout (Oncorhynchus mykiss)

Influence of dietary glucan and vitamin C on non-specific and specific immune responses of rainbow trout (Oncorhynchus mykiss)

Vertebrae fusion in Atlantic salmon (Salmo salar) : Development, aggravation and pathways of containment

Growth, digestibility and fatty acid utilization in large Atlantic salmon (Salmo salar) fed varying levels of n-3 and saturated fatty acids