Utilization of diets with different fish oil content in common octopus ( O ctopus vulgaris Cuvier, 1797) and resulting changes in its biochemical composition

The aim of the present work was to obtain the lipid utilization of O ctopus vulgaris supplying formulated semi‐moist diets with different contents in cod oil (reduced from water content): 0 g kg −1 (A0, 138 g kg −1 lipids DW ; N  = 4), 100 g kg −1 (A100, 286 g kg −1 lipids DW ; N  = 6) and 200 g kg −1 (A200, 388 g kg −1 lipids DW ; N  = 6). The rest of the ingredients were constant in the three diets: 200 g kg −1 gelatin, 100 g kg −1 egg yolk powder, 150 g kg −1 freeze‐dried T odarodes sagittatus and 50 g kg −1 freeze‐dried S ardinella aurita ). Survival was 100% with the three diets. The highest absolute feeding (15.8 ± 1.2 g day −1 ), growth (9.6 ± 1.4 g day −1 ; 0.91% BW  day −1 ) and feed efficiency rates (60.3%) were obtained with diet A0. This diet also showed greater retention of lipid and protein than A100 and A200. Protein digestibility was above 95% in all of the diets. Only diet A0 led to a high lipid digestibility coefficient (81.25%), which fell drastically to 12.3% in A200. It was notable the high polar lipid digestibility rates (83–89%) respect to neutral lipids (2–87%) in all diets. The best results were obtained with lipid feeding rates of around 1 g day −1 and a suitable lipid content on 130–140 g kg −1 DW in formulated diets for O. vulgaris .