Feeding plasticity of Trematomus newnesi (Pisces, Nototheniidae) in Terra Nova Bay, Ross Sea, in relation to environmental conditions

Forty-three and 49 specimens of the Antarctic fish Trematomas newnesi were collected in the coastal waters of Terra Nova Bay, Ross Sea, during Decembe r 1994 and February 1998, respectively. The dietary composition of the two fish samples was determined by means of stomach content analysis and then c ompared. In general, as reported in most of the previous studies, planktivo ry appeared to be the main feeding habit of T. newnesi. However, the differ ent environmental conditions occurring in the study area in the two periods investigated, such as the degree of the sea-ice coverage and the related a mount of light available below the ice, influenced the food composition of T. newnesi. In December 1994, the whole area investigated was covered by a thick layer of sea ice and the diet of T. newnesi consisted of few prey tax a. Some species that characterize the so-called "cryopelagic habitat", such as the euphausiid Euphausia crystallorophias and the copepod Metridia gerl achei, were by far the most important prey, followed by amphipods and the p teropod Limacina helicina. Conversely, the ostracod Alacia belgicae and lar val stages of fish (Pleuragramma antarcticum) were consumed occasionally. I n late summer (February 1998), the lack of sea-ice coverage and changes in the associated fauna influenced the feeding habit of T. newnesi. In this pe riod the food spectrum appeared to be more diverse, revealing an active fee ding search in the water column. The bulk of food was composed of several p rey groups, such as E. crystallorophias, hyperiid amphipods (Hyperiella dil atata), copepods, L. helicina and several species of fish larvae. Present d ata provide evidence of a marked feeding plasticity of T. newnesi, in respo nse to diverse environmental conditions that characterize the High-Antarcti c Zone.