Fatty acid composition of the common octopus, Octopus vulgaris, in relation to rearing temperature and body weight

Octopus vulgaris is considered a candidate for aquaculture and its growth performance is dependent upon temperature and body weight. The aim of this study was to investigate the effects of temperature on the fatty acid composition of O. vulgaris in relation to body weight (60-663 g). The experiments were performed in a closed seawater system with controlled temperature (15, 20 and 25 °C). The octopuses were fed on squid (Loligo vulgaris). O. vulgaris showed a high content of polyunsaturated fatty acids (51.32-57.62% total fatty acids), particularly n - 3 highly unsaturated acids (38.01-52.73% total fatty acids). At each temperature, the proportion of some fatty acids was highly (P < 0.0001) related to body weight. Specifically, 18:1n - 9, 18:1n - 7, 18:2n - 6, 20:4n - 6, 22:4n - 6 and 22:5n - 6 decreased, while 20:5n - 3 (EPA) and 22:6n - 3 (DHA) increased, with increasing body weight at 20 and 25 °C. The opposite was observed at 15 °C. Total polyunsaturated and n - 3 highly unsaturated fatty acids (HUFA) decreased in larger octopuses at 15 °C, as well as in smaller octopuses at 25 °C, whereas total saturated, monounsaturated and n - 6 HUFA increased. Thus, total unsaturated fatty acids showed a relatively small variation (60.53-63.96% total fatty acids) and the mean unsaturation index was similar at 15 and 25 °C. Arachidonic acid (2.4-9.6% total fatty acids) was inversely related to EPA and DHA, and positively to 18:2n - 6, 22:4n - 6 and 22:5n - 6. It is noted that arachidonic acid is not an essential fatty acid for the common octopus. It is concluded that the fatty acid composition of O. vulgaris was influenced by temperature and body weight, but with an n - 3/n - 6 ratio of more than 3 and a DHA/EPA ratio of more than 1.5. The common octopus could be an excellent source of arachidonic acid, containing sufficient n - 3 HUFA levels, in low temperatures for large individuals and in warm temperatures for small ones.