Biodiversity for the protein sources utilized in feeds for intensive fish culture.

The reduction of dependence on fishmeal (FM) in is compulsory for a sustainable growth of aquaculture. Concerning the protein component, feed companies turned towards the use of alternative protein sources, as vegetable meal (VM), that today vary in the range 48-68% in commercial aquafeeds. Nevertheless, elevate VM in the diet may not always be tolerated by fish, resulting in gut inflammations and histological damages, with reduced digestive functionalities and integrity. Microbiota composition is influenced by the diet. The digestive apparatus adjusts to changing of diet composition, with the mucosal defence system providing the gastro intestinal tract (GIT) with mucopolysaccarides that protect the intestine walls from injurious agents; moreover, a damaged fish gut may become an important infection route for microbial pathogens in fish. The GIT contributes to body health in many ways: of particular interest in this context is the emerging concept of "gut health". It covers multiple positive aspects of the gastrointestinal tract, such as the absence of gastrointestinal illness, normal and stable intestinal microbiota, and effective immune status, that are also able to determine a state of well-being. Among protective nutraceuticals that are produced with anaerobic bacteria fermentation and may be add to feed as well, the short chain fatty acids play a relevant role. Among them, butyrate could have a pivotal role in the context of "nutritional welfare”: in particular, acting as an anti-inflammatory agent, providing an enterocytes trophic action, acting as promoter of oligopeptides transport, promoting production of antinflammatory cytokines, thus positively acting on fish growth. Also the molecular biomarkers, that may early describe the progression of any intestine damages, could be useful tools to tune an appropriate nutritional strategy. In feeding challenges, a scoring system has been set up to assess the diet-related histological changes in different gut tracts; such system showed that histological changes occur early, within the first 10 days after the new diet administration. The intestine conditions shown a sort of adaptation trend after 40-50 days trial, after which the score trends tend to recover toward the initial level. We speculate that, as long as such changes are reversible, healthy fish is able to respond quickly at diet variation returning toward the initial condition within 1-2 months. However, we have to take in account several parameters (growth performances, histological changes, molecular biomarker levels, gut microflora biodiversity, rearing condition etc.) to compose a comprehensive picture on the animal nutritional welfare. The present work has enabled to evaluate the zootechnical performances of four diets at different level fishmeal substitution with protein vegetable sources. The result showed that seabass may be fed with aquafeed containing around 20% of fishmeal without relevant difference in growth performance from feed richer in FM. The great importance of biodiversity concept, in fishing resources for feed as well as in maintaining the fish gut microbiota in good condition, is evident with this study.