ISOLATION OF PUTATIVE PROBIOTICS WITH CHITIN-METABOLIZING ABILITIES FROM EUROPEAN SEA BASS (Dicentrarchus labrax) GUT MICROBIOTA

In aquaculture, finding alternative ingredients to fish meal (FM) is urgently needed, since the depletion of fish wild stocks has led to a decrease in FM availability, thus increasing FM price. Plant feedstuffs (PF) may partially replace FM in aquafeeds (Tacon et al. 2011). However, PF use has its own drawbacks. In terms of resources management, PF are in direct competition with human food and have a high demand for land and water for production. Moreover, the presence of antinutritional factors, and, imbalanced amino acid profile, diminishes its effectiveness as an FM substitute in aquafeeds (Gatlin et al. 2007; Henry et al. 2015). Insect meal (IM), recently authorized for use in aquafeeds, positions itself as a promising aquafeed commodity due to its high protein content, balanced amino acid profile and high lipid contents. However, insects are also rich in chitin, a structural polysaccharide present in the insect's exoskeleton, whose non-digestibility has been linked with lower fish performance and nutrient digestibility (Henry et al. 2015; Gasco et al. 2019). To overcome the chitin impairments of IM inclusion in aquafeeds, IM can be submitted to chemical or enzymatic treatments to promote chitin breakdown before being added to diets, but these processes have high costs, low yield, residual acidity, and may result in serious environmental pollution (Harish Prashanth and Tharanathan 2007). Alternatively, probiotic (PRO) bacteria, knowing to possess chitinase activity (e.g. Bacillus subtilis, (Askarian et al. 2013)), could be a solution. As such, this proposal aims to isolate, from European sea bass gastrointestinal tract, PRO bacteria capable of producing chitinases to improve the use of high IM-containing diets, supporting cost-effective fish growth without compromising welfare and health status.