Antarctic toothfish

Fully grown, antarctic toothfish, (like their warmer-water relatives, the Patagonian toothfish, D. eleginoides) may grow to more than 1.7 m (5 ft 7 in) in length and 135 kg in mass, twice as large as the next-largest Antarctic species of fishes. Being large, and consistent with the unstructured food webs of the ocean (i.e., big fish eating little fish regardless of identity, even eating their own offspring), the Antarctic toothfish has been characterized as a voracious predator. Furthermore, by being by far the largest midwater fish in the Southern Ocean, it is thought to fill the ecological role that sharks play in other oceans. As an adaptation to that role, the Antarctic toothfish is one of only five notothenioid species that, as adults, are neutrally buoyant. This buoyancy is attained at 100–120 cm in length and enables them to spend time above the bottom without wasting energy. Both bottom-dwelling and mid-water prey are, therefore, available to them. Most other notothenioid fish and the majority of all Antarctic fishes, including smaller toothfish, are confined to the bottom. Coloring is black to olive brown, sometimes lighter on the undersides, with a mottled pattern on body and fins. Small fish blend in very well among the benthic sponges and corals. …

Over the continental shelf, Antarctic toothfish feed on shrimp (Nauticaris spp.) and small fish, principally another neutrally buoyant nototheniid, the Antarctic silverfish (Pleuragramma antarcticum). This loosely schooling species is also a major prey of Adélie (Pygoscelis adeliae) and emperor penguins (Aptenodytes forsteri), Weddell seals (Leptonychotes weddellii) and Antarctic minke whales (Balaenoptera bonaerensis). Therefore, competition for prey among toothfish and these other mesopredators (middle trophic level predators) could be very important. The large Antarctic toothfish are eaten by sperm whales (Physeter macrocephalus), killer whales (Orcinus orca), Weddell seals, and possibly colossal squid (Mesonychoteuthis hamiltoni). Toothfish that are dwelling on the bottom, particularly those caught during the summer on the continental slope, eat mainly grenadiers (Macrouridae), but also feed on other smaller fish species and skates (Raja spp.). They also feed on the colossal squid. Antarctic toothfish have been caught to depths of 2200 m, though based on commercial fishing effort, few occur that deep.