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The trophic ecology of the emerald notothenTrematomus bernacchiiwas investigated using a sample of 284 specimens collected in the coastal waters of Terra Nova Bay (Ross Sea) during the summer season 1990-1991. The stomach-content analysis provided data on feeding habits and trophic niche breadth. Overall, 72 taxa of food items were identified; the most important as prey were infaunal and epifaunal polychaetes, amphipods and molluscs. Food of secondary importance comprised isopods, pycnogonids, fish and fish eggs. Several other taxa, such as euphausiids, mysids, decapods, echinoids, holothurians, priapulids and thaliaceans constituted food eaten in very small amounts and only occasionally. On the basis of their diet,T. bernacchiican be considered generalized feeders, with a wide niche breadth composed almost exclusively of benthic organisms. A cluster analysis was conducted to compare stomach-content data of subsamples selected on the basis of fish size and sampling depth, aiming to determine diet diversity and niche breadth, as well as factors involved in reducing intraspecific competition for food resources. Diet was different for fish sampled in shallow (=90 m depth) and deeper waters (>90 m depth): while the first group fed mostly on bivalves (Adamussium colbecki) and amphipods, the latter preferred infaunal-epifaunal polychaetes. Conversely, fish size did not contribute significantly to diet diversification. According to our data and published data on feeding behaviour and sensory ecology, we conclude that in this species the intraspecific competition for food is reduced, either through habitat heterogeneity or different foraging strategies. [ABSTRACT FROM AUTHOR]

A study of feeding ecology in Trematomus hansoni Boulenger 1902 and Trematomus loennbergii Regan 1913 was carried out from samples collected in the austral summer 1990-1991 off Terra Nova Bay, Ross Sea. T. hansoni was caught between 35 and 566 m and T loennbergii between 311 and 543 m. Stomach contents analysis shows that T. loennbergii relies on a wider range of prey than T. hansoni. Fish and decapods are the main food resources of T. loennbergii, which feeds also on epifaunal and tube-dwelling polychaetes. T. hansoni mostly relies on fish resources that are made up of juvenile stages of fish and eggs. Despite the common area occupied by the two species, the interspecific competition is mostly mitigated due either to taking different prey or to taking different amounts of the same prey. [ABSTRACT FROM AUTHOR]