Suborder Notothenioidei

Suborder Notothenioidei

The notothenioids are commonly referred to as the icefishes ( see Fig. 18.9). The suborder is restricted primarily to high latitudes of the southern hemisphere,with greatest diversity in benthic habitats of Antarctica.These cold water fishes show numerous physiological and behavioral adaptations to prevent their tissues from freezing, including the production of a variety of glycoprotein antifreezes (see  Coping with temperature extremes). The bovichtids of Australia, New Zealand, and southern South America are considered the stem group for the rest of the suborder. Nototheniid cod icefishes are predominantly benthic, with some secondarily pelagic species that achieve neutral buoyancy by depositing lipids in their muscles and by reduction of skeletal material, two adaptations to water column existence that occur convergently in other families derived from benthic ancestors (e.g., cottoid Baikal oilfishes, andmany deepsea forms). The best known nototheniid is the Patagonian Toothfish (or Chilean seabass), Dissostichuseleginoides, a large (to 2.4 m, 130 kg), long-lived (to 50 years), slow reproducing, and grossly overfished benthopelagicpredator (Fig. 15.21). The channichthyidcrocodileicefishes are well studied because they lack red blood cells,hemoglobin, and myoglobin, making their blood and fleshcolorless. These traits probably reflect the high amount of dissolved oxygen in cold Antarctic waters.