Larval condition of Merluccius hubbsi (Marini, 1933): preliminary results from field Studies

Abstract

Argentinean hake, Merluccius hubbsi, is one of the most important fishery resources of the South-western Atlantic Ocean. It inhabits waters from Cabo Frío in Brazil (22°S) to southern Argentina (55°S) at depths ranging from 50 to 500 meters. There are two fishing stocks, north and south of 41°S. Southern or Patagonian stock, which will be the subject of this study, is the most important fishing stock, accounting for 85% of the total estimated biomass for this species. During the last years of the 90´s decade the spawning biomass of both stocks dramatically decreased, which was mainly attributed to the increased fishing pressure on this resource which was developed during previous years. It is widely accepted that to understand recruitment variability is necessary to study the factors that determine the survival of the early stages of development. Nutritional condition indexes have been widely used to determine starvation in larvae caught in the ocean. Many studies suggest that RNA/DNA index is one of the best indicators of the nutritional status of various marine organisms and is currently the most widely used biochemical indicator of nutritional condition of fish larvae. Condition of M. hubbsi larvae was estimated employing field collected material; RNA/DNA index was calculated along larval development for the first time for this species. It has been observed that larval condition differs between developmental stages. Larval condition index increases during pre-flexion and flexion stages, stayed stable during post-flexion stage and showed an important decrease at the end of the latter stage and the beginning of transformation larvae stage. This finding indicates that the transition from post-flexion to transformation larvae stage represents a critical period with a significant reduction in larval abundance and condition. The study of nutritional condition represents a useful tool for identifying favourable nursery areas, provides valuable information for a comprehensive management of a population subject to overfishing, and could be taken into account in order to establish restricted areas and appropriate closure periods