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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.

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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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Four ongrowing cycles of common octopus (Octopus vulgaris), each with two stocking densities, were carried out in an offshore area in order to evaluate the effect of the following variables on growth (G, % body weight day−1) and mortality (M, % day−1): weight (W, 0.5–3.0 kg), temperature (T, 14–26 °C), stocking density (SD, 6–46 kg m−3), size dispersion, expressed as coefficient of variation (CV, 13–42%) and significant wave height (SWH: 0.4–1.2 m). The assays were performed in an 8 m3 stainless‐steel floating cage divided into two compartments of 4 m3 each. For the range of temperatures considered (14–26 °C), G depended significantly on T and SWH, with maximum G values being obtained at 18.5 °C and with an important negative effect of SWH. M depended significantly on T, W and CV, mortality being minimal at 18 °C. The two other variables had an antagonistic effect, mortality increasing with greater size dispersion – suggesting that animals should be graded throughout the process – although the effect diminished as the sizes increased. The results point towards two alternatives for the commercial ongrowing of octopus under the particular conditions of the present study: (A) two ongrowing cycles of 3.5 months to reach a final weight of 2.5 kg or (B) one 5‐month cycle to reach a final weight of 3.5 kg.

The aim of the present work was to test the capacity of Octopus vulgaris to use carbohydrates supplied in three diets: a diet without added carbohydrates (diet C0: 500 g kg À1 water, 200 g kg À1 gelatine, 100 g kg À1 egg yolk powder, 50 g kg À1 freeze-dried Sardinella aurita and 150 g kg À1 freeze-dried Todarodes sagittatus) and two obtained by substituting 50 g kg À1 of T. sagittatus by glucose (diet GLU50) or by starch (diet STA50). The most stable and best-accepted diet was STA50 (SFR 1.26%BW day À1 ) although there were no significant differences in the growth rates obtained with the three diets: 10.12 g day À1 , 9.37 g day À1 and 11.22 g day À1 for C0, GLU50 and STA50, respectively (P > 0.05). The feed efficiency indices were better for GLU50, of particular note being the protein productive value of 71.88% and a feed conversion ratio lower than 1. Protein and lipid digestibility were similar in all the three diets (96-98% for proteins and 85-94% for lipids), whereas carbohydrate digestibility was higher in GLU50 (98%) than in C0 (84%) and STA50 (0.33%). The content of carbohydrates increased in muscle and the digestive gland as a consequence of the increased carbohydrates intake.