Combined effects of temperature and body weight on growth and protein utilization of the common octopus, Octopus vulgaris

Octopus vulgaris is considered a serious candidate for rearing, in terms of its biological and market potential: easy adaptation to captivity conditions, high growth rate and high market price. The aim of this study was to examine the combined effects of temperature and body weight on specific growth rate (SGR, % day− 1), absolute growth rate (AGR, g day− 1), absolute feeding rate (AFR, g day− 1), feed efficiency (FE, %), protein retention efficiency (PRE: [g protein gain g protein ingested− 1] × 100), energy retention efficiency (ERE: [kJ gain kJ ingested− 1] × 100), proximate composition and P/E ratio (protein/energy) of the common octopus. The experiments were performed in a closed system with controlled temperature (15, 20 and 25 °C). The octopuses were fed on squids (Loligo vulgaris). In the multiple regression equations estimated for SGR, AGR, AFR, FE, PRE and ERE, the linear and quadratic effects of temperature, as well as the linear effects of body weight were significant. In addition, the interaction effects of temperature and body weight were significant for SGR, AGR, FE, PRE and ERE; the temperature for maximum response decreased with increasing size, being 25 °C for octopuses of 50-150 g and 15 °C for animals of 200-600 g. The weight exponent in the relationships of these indices vs. body weight decreased with increasing temperature. The levels of SGR, FE, PRE and ERE varied slightly with temperature in individuals of 150-200 g, and the respective response surfaces showed a plateau within this range of body sizes independently of temperature. The temperature for maximum AFR was estimated to be 21.88 °C independently of body weight. Proximate composition and P/E ratio of octopuses were not affected by temperature or body weight. It is concluded that temperature should be adjusted according to the body weight of O. vulgaris for optimizing the economic viability of rearing. Temperature should be high for small individuals (50-150 g) and should be reduced gradually in order for animals larger than 200 g to be reared at low temperature. Therefore, O. vulgaris should be reared in closed systems with temperature control.