The aim of this study was to evaluate growth, biochemical composition and dietary nutrients utilization in Octopus vulgaris fed on four diets based on bogue Boops boops, from different origin and in two presentations: fresh discarded bogue (aquaculture by‐product) (DB‐f), fresh wild bogue (low price trash species) (WB‐f), discarded bogue agglutinated moist diet (DB‐m) and wild bogue agglutinated moist diet (WB‐m). Diets based on DB showed higher lipid content (19–26% dw) than those based on WB (5–6% dw). Octopuses fed on DB‐based diets showed higher growth (1.5–1.9% day−1) and higher protein efficiency ratio (0.64–0.69) than those fed on WB‐based diet (1.1–1.5% day−1 and 0.36–0.37 respectively), which suggests good utilization of dietary lipids and also a possible protein sparing effect by lipids in O. vulgaris. Octopuses fed on diets presented fresh showed a higher growth (1.9–1.5% day−1) and a higher feed efficiency (62–65%) than those fed on agglutinated diets (1.1–1.5% and 52–60% day−1 respectively). Regarding fatty acids, the digestive gland clearly reflected dietary lipid and fatty acid profile, while muscle showed a more stable composition. Low dietary ARA content reflected in octopus tissues, especially in specimens fed on DB‐based diets, which did not seem to affect growth during the experimental period.

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Estefanell, J., Socorro, J., Roo, F. J., Fernández-Palacios, H., and Izquierdo, M. 2010. Gonad maturation in Octopus vulgaris during ongrowing, under different conditions of sex ratio. – ICES Journal of Marine Science, 67: 1487–1493. Octopus vulgaris is a suitable candidate for aquaculture, but there are problems with breeding in captivity, such as aggressive behaviour among males and the frequent death of females after the eggs hatch. To avoid these problems and further understand the sexual maturation of common octopus in captivity, males and females were reared together and separately under similar culture conditions. In all trials, the initial rearing density was 10 kg m−3. Females (n = 15, sex ratio 0:1) and males (n = 11, sex ratio 1:0) were kept in circular tanks, and a mixed group (n = 209, sex ratio 4:1) in floating cages. Trials started in November 2008 and octopuses from each treatment were examined macroscopically and histologically in December and January to assess sexual maturation. All the males matured, regardless of the sex ratio during rearing, as did all females in the mixed group. In contrast, a large proportion of the females kept isolated from males was still immature in December and January. Although maturation was successful in floating cages, there was 76% mortality there, in contrast to the zero mortality in tanks. Moreover, most of the dead octopuses from the cages were in post-reproductive condition, with a low digestive gland index, suggesting that this was natural post-reproductive mortality. Therefore, sex segregation is deemed advantageous to avoiding early mortality.

Recently most research on cephalopod culture has focused on the development of new specific enrichments for paralarvae and compound feeds for juveniles and sub‐adults. However, little research has been conducted in order to test new rearing systems, specifically designed to meet the particularities of these species. This experiment was set to compare the biological performance of Octopus vulgaris reared under traditional group conditions in floating cages (5 m3) and individually in net cages (80 L), in two successive ongrowing trials. Octopuses (1565 ± 263 g) were fed a mixed diet containing crab and fish during 60 d. In general, higher mortality was observed in octopus reared under group conditions (28.1–36.7%) rather than individually (0–12.5%), related to breeding behavior and to weight dispersion along both trials. This led to highest biomass increment in octopus reared individually. However, the group rearing system had a positive effect on growth, reflecting in higher biomass increment and food conversion rates until 40–50 d of rearing. Accordingly, in order to maximize profitability of traditional group on growing, periodic grading and selection of males during the reproductive period are recommended. In addition, no difference in proximate composition and fatty acid profile was found in muscle regardless of rearing system.

Two fresh diets were tested on the biological performance of males and females of Octopus vulgaris under industrial rearing conditions in floating cages. The presence of females could potentially release paralarvae to the natural environment (‘integrated aquaculture’). Octopuses were fed on a single diet of bogue (aquaculture by‐product), and on a mixed diet (60–40% crab‐bogue), in two trials. In Trial 1 (918 ± 125 g), growth was higher in octopuses fed on the mixed diet (1.9–2.0%d−1) than in those fed on the bogue diet (1.8–1.9%d−1) irrespective of sex, and mortality was 3% regardless of sex and diet. In Trial 2 (1483 ± 269 g), growth was higher in males fed on the mixed diet (1.8%d−1) than in males fed on the bogue diet (1.4%d−1), both higher than females (1.1–1.3%d−1), and mortality was 22–28% regardless of sex and diet. Best biological performance in trial 1 was related to the lack of functional maturation in females, evidence by the low average gonadosomatic index (2.0–3.6%) in comparison with trial 2 (8.8–11.4%), regardless of diet. No correlations between final weight and sexual maturity indices were found, so the length of the rearing period to maximize biomass increment or to release paralarvae depends on functional maturation in females.