Marine by-products tested as feed for almaco jack Seriola rivoliana and their effect on fatty acids and sterols in different tissues.

Marine by-products can compose up to 70% of the total weight of produce from fisheries; most of these by-products are discarded. However, these by-products are rich in highly unsaturated fatty acids that are not synthetized by most marine animals that are produced by aquaculture. Here, we used three marine by-products (shrimp head, Catarina scallop viscera, and Pen shell viscera) to produce meals without the step used to separate lipids as is traditionally done; this separation can promote hydrolysis of lipids and ultimately, oxidation of fatty acids and sterols. Lipid-rich meals were used to partially substitute commercial fishmeal on feeds that were used to grow almaco jack (Seriola rivoliana) juveniles for 10 weeks. The content of 20:5n-3 and 22:6n-3 in tissues of fish fed shrimp and Pen shell presented values similar to controls, but the former had had a better effect on growth, lipid, and phytosterols levels. However, Catarina meal had lower concentration of 20:4n-6 and 22:6n-3 but higher proportion of 20:4n-6 in muscle and 22:6n-3 in liver, indicating a selective conservation in relation to other fatty acids. Catarina meal contained traces of 18:5n-3 (0.02 g/kg) indicating that these scallops, albeit their healthy aspect, were in contact with toxins (okadaic acid) produced by dinoflagellates, a setback that needs to be addressed previous to meal manufacturing. In conclusion, marine by-products processed to maintain lipid composition can be used to reduce the use of fishmeal in the diet, and their use improve the lipid content and growth compared to control diet with fishmeal.