Seasonal changes in the biochemical composition of Octopus vulgaris Cuvier, 1797, from three areas of the Portuguese coast

The aim of this work was to investigate biochemical changes during the reproductive cycle of the common octopus, Octopus vulgaris, Cuvier, 1797. Proximate composition, fatty acids, cholesterol and amino acids were determined monthly in the mantle of O. vulgaris caught off in three different areas of the Portuguese coast. The moisture content exhibited significant seasonal and spatial variations, with a maximum value in Viana do Castelo in April (81.4%) and a minimum value in Tavira in October (76.5%); the mineral content tended to be similar to the results of other studies (1.4-1.9%). Nitrogen compounds were the major organic compounds (16.1-20.7%) and seem to be the most important energetic fuel in sexual maturation, spawning and brooding. In fact, the maturation of gonads and periods of feed deprivation (during brooding) can result in tissue depletion with marked decreases in the content of protein in muscle. With the profiles of SDSPAGE it can be speculated that the exhaustion of these energetic sources, at the end of the reproductive cycle, might be explained by the decrease of the major myofibrillar proteins content (paramyosin, myosin and actin), due to the enhancement of the protease activity in the muscle. Glutamic acid (2.1-2.7 g 100 g(-1)), aspartic acid (1.4-1.9 g 100 g(-1) wet weight) and leucine (1.3-1.8 g 100 g(-1) wet weight) were found to be the major components within muscle proteins. The total lipid content (0.1-0.6%) and the major polyunsaturated fatty acids DHA (C22:6w3) and EPA (C20:5w3) showed variations which could be related to oogenesis and spermatogenesis. The cholesterol content can be correlated with the rapid maturation process, because the production of sexual hormones are related with the cholesterol metabolism. Some data of metabolic state, sexual maturation and reproduction, related with the biochemical composition of Octopus vulgaris, are certainly important to a better knowledge of octopus life-cycle.