Life history traits of a poorly known pelagic fish, Aethotaxis mitopteryx (Perciformes, Notothenioidei) from the Weddell Sea

Amongst the nototheniid subfamily Pleuragramminae, Aethotaxis mitopteryx is an infrequently collected high Antarctic species with an array of morphological and physiological adaptations supporting an evolutionarily derived benthopelagic lifestyle. The present study deals with some poorly known life history traits of this species, counting on 79 specimens collected in the Weddell Sea during 2014 and 2015 austral summer. Annulation pattern in sagittal otoliths were used to assess population age structure and growth rate, while macroscopic and histological analyses of gonads were performed to estimate reproductive status and features of gametogenesis. The sex ratio of the sampled population was close to parity, with females significantly larger than males. Based on the von Bertalanffy growth model, females attained a larger maximum size (40 vs. 27 cm) at a lower rate (0.05 vs. 0.12 years−1) than males. Individual longevity was remarkable in both sexes, females and males attaining 62 and 32 years of age, respectively. Females showed group synchronous oocyte development and presumed high reproductive effort, as indicated by the large size of residual hydrated oocytes in regressing individuals (4.6–4.8 mm). Body sizes at sexual maturity were 33 and 19 cm in females and males, corresponding to 32 and 11 years of age, respectively. All specimens were caught far from the reproductive season. From an evolutionary perspective, it appears that the process of pelagization similarly influenced the life strategies of the species within the clade Pleuragramminae, which shared high reproductive effort linked to early sexual maturity, slow somatic growth and long life span.