Age, Growth and Maximum Size of Antarctic Notothenioid Fish — Revisited

Abstract

The temperature of the Southern Ocean has undergone an overall reduction from about 20 degree C to -1.8 degree C over the last 55-60 million years. To date, the Southern Ocean is characterized by low temperatures ranging from +3 degree C close to the South Polar Frontal Zone to -1.86 degree C in the vicinity of the Antarctic continent and a strong seasonality and patchiness of primary productivity. The Antarctic coastal fish fauna consists of about 140 species of 18 families [1]. This fauna is dominated both in terms of species and biomass by a single endemic perciform suborder, the Notothenioidei. Notothenioidei comprise a variety of ecomorphological types ranging from small sculpin-like to large hake-like forms [1-3]. Two coarse groups of coastal species can be distinguished according to their geographical distribution: lesser-Antarctic/subAntarctic species and high-Antarctic species [4]. Although low temperature has most likely played a dominant role in the evolution of the present fish fauna, other factors, such as climatic cycles, isolation, habitat loss, and seasonality in food availability have probably also been important [2]. Antarctic notothenioid fish show a variety of adaptations at the molecular level, such as freezing resistance, tubulins, which polymerize at -2 degree C, the conductivity of neurones and high turnover rates of enzymes, in order to maintain function in their extreme thermal environment [2,5]. The rates of complex physiological systems are frequently slower in Antarctic species than in temperate species. Growth is a complex process that is subject to a number of controls and limitations at a variety of levels, which makes it difficult to determine which particular factor is the strongest in controlling growth rate [6]. Temperature and other environmental variables, such as light levels, food availability and quality, reproduction and activity are all likely to affect growth [6-9].