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

The aim of the present work was to obtain the lipid utilization of Octopus 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 Todarodes sagittatus and 50 g kg−1 freeze-dried Sardinella 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.