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 À1 (A0, 138 g kg À1 lipids DW; N = 4), 100 g kg À1 (A100, 286 g kg À1 lipids DW; N = 6) and 200 g kg À1 (A200, 388 g kg À1 lipids DW; N = 6). The rest of the ingredients were constant in the three diets: 200 g kg À1 gelatin, 100 g kg À1 egg yolk powder, 150 g kg À1 freeze-dried Todarodes sagittatus and 50 g kg À1 freeze-dried Sardinella aurita). Survival was 100% with the three diets. The highest absolute feeding (15.8 AE 1.2 g day À1 ), growth (9.6 AE 1.4 g day À1 ; 0.91% BW day À1 ) 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 À1 and a suitable lipid content on 130-140 g kg À1 DW in formulated diets for O. vulgaris.
In this work, we study the variations in concentration (mg 100 g−1 dry weight) and total content (mg individual−1) of different lipid classes in muscle and the digestive gland of Octopus vulgaris during an 8‐day starvation period. In all the samples analysed, polar lipids (PL) predominated in muscle (267.3–337.2 mg 100 g−1) compared with neutral lipids (66.9–104.7 mg 100 g−1). A significant positive tendency was observed in muscle for the content and concentration of monoglycerides as a consequence of starvation (P < 0.05). Furthermore, a higher cholesterol (CHO) content was detected in this tissue after the fourth day of starvation compared with the fed animals (P < 0.05). Neutral lipids predominated in the digestive gland (12 958–14 151 mg 100 g−1) compared with PL (3157–6517 mg 100 g−1), with triglycerides, free fatty acids and monoglycerides being the major lipid classes. The concentration of PL and monoglycerides showed a positive trend with starvation, while the triacylglycerol showed a negative tendency (P < 0.05). The results suggest that triglycerides and CHO are transported simultaneously from the digestive gland to the muscular tissues during starvation and the preferential use of PL and CHO during growth phases. It was estimated that lipids contributed 26% of the energy costs of the animals during starvation, mainly in the form of triglycerides from the digestive gland.
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