Gonad maturation in Octopus vulgaris during ongrowing, under different conditions of sex ratio

Abstract

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.