Dr. Urzua-Osorio, Angel

In the Southeast Pacific Ocean, Xiphias gladius migrates through the Chilean coastal zone for feeding. Here, it forages for different prey items from autumn to spring, acquiring a great variety of energy and nutritional reserves. We evaluated seasonal variations in the biochemical reserves (i.e., contents of lipids, proteins, and glucose), total energy content and fatty acid profile of specimens captured during the austral autumn, winter, and spring. Our results show that higher amounts of lipids were found in the winter and spring, while protein and glucose were higher in the autumn. Thus, the energy content showed significant differences, with higher levels in winter and spring. Furthermore, the fatty acid profile was more diverse in the spring than the autumn and winter and was characterized by higher amounts of polyunsaturated fatty acids. These findings suggest that temporal changes in the biochemical reserves, total energy content and fatty acid profile support the idea of a “trophic migration” (i.e., the feeding period) established by the dynamics of fishery fleets. The high amounts of lipids and diverse fatty acid profile found in the spring could indicate the end of the trophic migration during this season. Thus, X. gladius may reach an optimum nutritional condition in the spring and make energetic adjustments to carry out its reproductive migration during the austral summer. Therefore, this species seems to meet the high energy demands of the reproductive season by foraging for a wide range of prey items from autumn to spring and storing an increased amount of lipids at the end of the feeding period. Overall, our data provides crucial baseline knowledge for future research on the ecophysiology of X. gladius, as well as for the management and conservation of this fishery resource under an ecosystem approach.

In marine invertebrates, the bioenergetic fuel available for fundamental physiological processes (growth, reproduction) may present intra-individual variability depending on the storage organ, sex and state of sexual maturity. This variability is considered relevant information for fishery management. In the squid Dosidicus gigas, an important fishery resource, we analyzed adult males (immature vs. mature) and females (immature I vs. immature II) off the coast of Chile. Their bioenergetic fuel (protein, glucose, lipid and fatty acid content-FAs) was quantified in different organs of the body (digestive gland, gonad and mantle). When comparing the organs of males at both stages of maturity, a greater amount of glucose and lipids were observed in the digestive gland than in the gonad and mantle, while a higher protein content was recorded in the gonad. In turn, the same tendency of biochemical variations among the organs was observed for the female at both stages. Regarding the FA profiles of the analyzed organs, the digestive gland had the highest mean proportion of FAs. However, no significant differences were observed related to sex and sexual maturity. According to the multivariate analyses for both sexes and maturity stages, the FA profiles of the mantle and gonad showed overlap and a high similarity, while the profile of the digestive gland was completely dissimilar. Our findings indicate that D. gigas from Chilean coastal waters showed, mainly in the digestive gland, high levels of all biochemical constituents, which are obtained through food and stored in their organs as bioenergetic fuel, and may then be used for the subsequent process of migration and reproduction in oceanic waters.