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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Settling velocity and total ammonia nitrogen leaching from commercial feed and faecal 50Several studies under laboratory conditions reported that 250-300 g kg -1 of ingested food is 51 voided as faeces (Butz and Vens-Cappell, 1982). Just as with food losses, a continuous 52 4 improvement in diet elaboration has led to a gradual reduction of faecal discharges to about 53 100-250 g kg -1 of ingested food (Cho et al., 1994; Talbot and Hole, 1994 Watling, 1994; Elberizon and Kelly, 1998; Chen et al., 1999a,b; Chen et al., 2003) MRAs for feed pellets (Table 3) showed that water temperature and pellet density had no (Table 5). Constant k was significantly higher at 25 ºC (P < 0.05) and in smaller feed pellets 215 (P < 0.05), while t a was significantly larger at 15 ºC (P < 0.05) but also for smaller pellets (P 216 < 0.05) ( 246The influence of pellet weight was also identified by other authors (Elberizon and Kelly, 247 1998; Chen et al. 1999b, Sutherland et al., 2006. In this study, we not only found that initial 248 pellet size determined settling velocity but also, unlike Chen et al. (1999b) authors state, the range of parameters studied was not so critical to the settling velocity. 270Despite this, we observed greater but non significant settling velocities at low temperature, as 271 Chen et al. (1999b) noted. These authors suggested that this could be due to the influence of 272 temperature on pellet density, although in our experiments we found that seawater 273 temperature did not affect pellet density.

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