Icefish belong to the Family Channichthyidae, which is one of eight families in the single perciform suborder Notothenioidei (Sidell and O’Brien, 2006). This particular family has come to dominate the coldest and most thermally stable marine environment on the planet (Mintenbeck et al., 2012). Temperatures are commonly around 1.86ºC, with little seasonal variation (range of +1ºC to -1.86ºC) (Clarke and Crame, 1989; Mintenbeck et al., 2012) (Figure 1). Despite the extreme temperatures, there is a high availability and stable content of oxygen in the water column as a result of vertical mixing. Oxygen saturation is also inversely related to temperature. Consequently, the Antarctic oceanic environment is exceptionally oxygen-rich (Sidell and O’Brien, 2006) (Figure 2). As a result of the extreme environmental conditions, endemic Antarctic fish are highly specialised and stenothermic (only present within a narrow temperature range), which has therefore restricted biogeographic distribution (Garofalo et al., 2009).
Figure 1. The annual oceanic surface temperatures (deg. C) for 2005. Isotherms mark bands of equal temperature. The lowest temperatures are commonly found around the Antarctic land mass and the Arctic Ocean (Source: National Oceanic and Atmospheric Administration (NOAA)).
Figure 2. The annual levels of oxygen in the oceans at 10m depth (ml/l) for 2009. Isotherms mark bands of equal oxygen concentration. Oxygen concentrations are highest in the polar regions (Source: National Oceanic and Atmospheric Administration (NOAA)).
This blog will explore the evolutionary history of icefish in accordance with the separation of the Gondwana land mass, the formation of the Antarctic land mass and the establishment of the Antarctic Circumpolar Oceanic Current. The subsequent environmental conditions were then conducive for adaptive radiation and the exploitation of a variety of oceanic ecosystem niches, due in part to a lack of competing taxa. Particular focus will then be given to the physiological mechanisms in icefish, such as the use of Antifreeze glycoproteins and the loss of haemoglobin, which have evolved to cope with low temperatures. Icefish are specifically adapted for life in an environment where there is little variation in physical conditions. Consequently, this fascinating family of fish will be highly vulnerable to any changes in oceanic conditions as a result of climate change.