Abstract
The slender scalyhead Trematomus lepidorhinus and the scaly rockcod T. loennbergii are closely related species with similar streamlined body morphology, epibenthic lifestyle and ecological niche. They are distributed in relatively deep waters on the continental shelf and slope of the Weddell Sea, although with some differences in preferential depth of occurrence. As previously reported, the peak of abundance of T. loennbergii (600–800 m) is generally deeper than that of T. lepidorhinus (200–500 m). In the present study, we investigated the role of depth as environmental factor in shaping key life history traits of these species, such as longevity and fecundity. Based on age estimates through otolith readings, males and females of T. loennbergii attained 15 and 20 years, whereas males and females of T. lepidorhinus attained 11 and 12 years, respectively. In both species, growth trajectories differed between sexes, although the growth performance was similar. Matching our and previous data on total and relative fecundities, T. loennbergii spawned a lower number of larger eggs per female and mass unit than T. lepidorhinus . Moreover, they adopted different reproductive strategies, as T. loennbergii likely spawned and hatched in autumn and early spring whereas T. lepidorhinus spawned and hatched in winter and early summer, respectively. In agreement with more general trends reported elsewhere in other fish communities, species living in deeper waters are characterized by longer life span and reduced fecundities.