The reproductive biology of two epibenthic species of Antarctic nototheniid fish of the genus Trematomus

Trematomus eulepidotus and T. loennbergii are two of the most common epibenthic fish in the waters of the High Antarctic continental shelf. We provide a macroscopic and histological analysis of the reproductive effort and gonadal development in both sexes. Samples were collected during benthic trawl surveys in the south-western Ross Sea in the 1996 and 1997 summer seasons. The aim was to define the reproductive characteristics of these two sympatric species and to examine the hypothesis that different reproductive strategies mitigate interspecific competition. We found that both species possess similar reproductive strategies including delayed sexual maturity, prolonged gametogenesis, group-synchronous oocyte maturation, a single spawning event per year and iteroparity. Both show a comparable reproductive effort in terms of potential fecundity with between 2000 and 20 000 eggs per female per season. Nevertheless, the two species exhibited a considerable difference in the timing of the breeding season, spawning in summer (T. eulepidotus) and in autumn (T. loennbergii). This gives rise to a mismatch in the time of appearance of larvae in the environment and probably leads to reduced