Lipid content of liver and muscle tissue of juvenile turbot (Scophthalmus maximus) fed with emerging protein sources

This study examined the growth response of juvenile turbot (Scophthalmus maximus) to diets with graded fishmeal (FM) replacement with plant, animal, and emerging protein sources (PLANT, PAP, and MIX) in comparison to a commercial-like diet (CTRL). The feeding experiment was carried out from April to July 2019 in the Centre for Aquaculture Research (ZAF) at the Alfred Wegener Institute for Polar and Marine research in Bremerhaven, Germany. The juvenile turbot (Scophthalmus maximus) were purchased from France Turbot (L'Épine, France) and acclimated to the recirculating aquaculture system (RAS) for 2 weeks prior to starting the 16 weeks experimental trial. To elucidate the effects of the protein sources and the level of FM replacement on the nutritional status of the fish lipid content of liver and muscle tissue were determined at the end of the experiment (t4). Muscle and liver samples (3 individual fish per tank; 15 fish per diet in total) were grinded under liquid nitrogen. Due to small volume, the individual samples of liver and muscle were pooled (n=5 tanks per diet) for the crude lipid content. Following the method of Folch et al. (1957) and Postel et al. (2000), the lipids in the muscle and liver tissue were extracted with 2:1 dichloromethanemethanol (v/v) and an aqueous solution of 0.88% potassium chloride (KCl) (w:v). Crude lipid content was determined gravimetrically to the nearest 0.001 g and calculated as the percentage of lipids of tissue wet weight.