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Fishery and Sea Resources& Aguado Giménez [20].In the literature the better growth resultsand the higher food intake were obtainedfor crab-fed octopuses [19, 29]. GarcíaGarcía & Cerezo Valverde [30] obtaineda comparable growth with a monospecificdiet based on crabs and with a mixeddiet (crab and bogue), although this latterdiet type showed the better feed efficiency.Smale & Buchan [31] and Cagnetta & Sublimi[19] stated that a mixed diet, based oncrustaceans and fish, may better meet thenutritional requirements of octopuses for ahigh growth rate.In this study, unexpectedly the octopusesfed on mixed diet showed a lower weightincrease than those fed exclusively onbogues. It was observed that the maximumgrowth and the best FCR do not coincidewith the highest AFR. The lowest FCR occursat AFR below those at which maximumgrowth occurs such as what is reportedin literature for fish [32, 33]. However,regarding growth, the statistical analysisdid not show significant differencesamongst all diet groups.The low AFR value observed in O.vulgarisfed mussels may indicate that this food hada low palatability, associated with a possiblelower nutritional value, even if the FEvalue was the highest.Nutrition is one of the most important factorsinfluencing the ability of cultured marineorganisms to exhibit its potential forgrowth and reproduction. Food quantityand food quality are the critical factors affectingthe juveniles growth under laboratoryconditions [34, 35, 3, 36]. Despite theincrease in the knowledge on nutritional requirementsof the fast-growing young octopuses[4, 7] there is lack of informationon these requirements for sub-adult growth[37]. García García & Aguado Giménez[20] in a study on the influence of diet ongrowth and nutrient utilization, showed alow growth in O. vulgaris fed diets withhigh lipids and low protein contents. Thismay be due to the fact that lipid digestibilityis low in cephalopods [38, 37] fortheir limited capacity to metabolize lipid[39, 40].In our case, all experimental dietary groupsshowed a low lipid content, with relativelylarge phospholipid and cholesterol fractionsand triacylglycerols as minor components,similar to the observations reportedin previous findings [41, 4, 27, 28]. Thisconfirms that lipid digestion is low, probablydue to the scarcity of an emulsifier inthe digestive tract [20].Diet had a clear influence on the octopuse’snutritional state. In a study on ongrowingof O. vulgaris, García García & CerezoValverde [30] analysed the furnished foodcomposition, and they reported a lipid contentof 0.79%, in the case of crabs (Carcinusmediterraneus), while for bogue a lipidcontent of 6.11%. At the end of the experiment,octopuses fed with bogues only,showed a lipid content of 0.34 ± 0.02%.This may be due to the fact that, evenif O. vulgaris requires a low quantity ofthe lipids, this species stores significantquantities of lipids in order to guaranteehigh growth rates [30]. Probably their useis mainly involved in the cell membranestructure [37]. In cephalopods, lipids arestored in the digestive gland and then transportedto the muscle to be used as an energysource [42]. The cephalopods are able tosynthesize sterols, although Voogt [43] reportedthat mollusks, can carry out slowlythis biosynthesis. For this reason, the mainlipids source comes from food, even duringreproduction [44].The results indicate that O. vulgaris is agood protein source according to Ozogul etal. [45]. Although crabs offer a source of2036