Abstract
The diet of Prionotus nudigula in coastal waters off Uruguay and northern Argentina (36°–41° S) and their variation in relation to body size, region and season were determined by analysis of stomach contents. Additionally, the trophic level of this species was estimated to establish its ecological role in this marine region. A total of 352 individuals were analysed, of which 308 (87.05%), ranging from 78 to 285 mm in total length (Lt), contained food. P. nudigula based its diet mainly on amphipods, followed by brachyuran crabs, shrimps and polychaetes. Cumaceans and isopods were also relevant prey but with a smaller contribution. Diet composition was strongly affected by body size and also by regions and seasons. Small individuals of P. nudigula consumed amphipods and small benthic fauna, whereas large individuals fed on brachyuran crabs, shrimps, cumaceans, hard benthic fauna and swimming prey. Furthermore, this species was able to consume larger brachyuran crabs and shrimps as it grew. P. nudigula exhibited regional and seasonal variations in its diet, showing changes in the consumption of its more important prey. Trophic level was 3.41, indicating that P. nudigula is a secondary consumer. This thorough investigation provides updated information on the trophic role of P. nudigula , representing a baseline for future investigations in the southwestern Atlantic Ocean.