Effect of including a seaweed meal in the diet on slaughter yield and major quality traits of rainbow trout (Oncorhynchus mykiss Walbaum, 1792)

Seaweeds are promising ingredients for aquafeed for improving fish growth and as source of n3 fatty acids. The present study aimed at assessing the effects on marketable and qualitative traits of rainbow trout (Oncorhynchus mykiss Walbaum, 1792) fillets of a low-level inclusion (5%) of a commercial mix of seaweed formulation in a soybean-rich diet. The fish were fed for 12 weeks and sampled immediately after the acclimation period (T0), after 6 weeks (T1) and 12 weeks (end of the trial, T2). Six fish per treatment were sacrificed at each sampling, individually weighed and submitted to the sectioning to obtain the body components that, after measurements, were needed to calculate the marketable indexes (condition factor, dressed and fillet yields, hepatosomatic index and viscerosomatic index). On fillets, physical properties such as pH, texture and color were measured and the cholesterol content, the proximate and the fatty acid composition were analyzed. Results revealed that the inclusion of seaweed mixture in a soybean rich diet significantly affected fillet yield and hepatosomatic index after 12 weeks of administration. The physical parameters of muscle, such as color, pH, water holding capacity and texture were not modified in comparison to the vegetable rich diet. Slight modifications in the proximate composition emerged at the end of the trial, especially concerning the protein content, which increased in parallel to a decrease of lipid content. However, the fatty acid profile of the muscle was deeply modified by the administered diets in comparison to the first 6 weeks. The inclusion level of seaweeds utilized in the present study was not sufficient for improving PUFAn-3 level of a diet rich in vegetable protein and oil