Antifreeze proteins in pelagic fishes from Marguerite Bay (Western Antarctica)

The Southern Ocean is home to two major types of fishes: the largely endemic suborder Notothenioidei and representatives of oceanic fish families that are widely distributed in the midwater and benthic environments elsewhere (e.g. bathylagids, myctophids, liparids, and zoarcids). In most regions of the coastal Antarctic, e.g. the Ross Sea, there is a distinct separation in the pelagic communities at the shelf break between the oceanics (off-shelf) and the endemics (on-shelf). Coincidentally, in much of the coastal Antarctic, the shelf break also marks the boundary between a water column entirely composed of the very cold (−2 °C) Ice Shelf Water and an oceanic profile that includes warmer circumpolar deep water (2 °C at 200 m) at intermediate depths. The distinct separation in pelagic communities observed in most coastal regions of the Antarctic is not seen on the western Antarctic Peninsula (WAP), where circumpolar deep water intrudes to form a warmer midwater and oceanic species are strongly represented. It was hypothesized that the cold ice-shelf water, lethal to fishes without antifreeze glycoproteins (AFGPs) in their blood, was excluding the oceanic species from most of the Antarctic continental shelf waters. To test the hypothesis, nine species of fish captured in WAP shelf waters were tested for the presence of AFGPs. The oceanic fish families analyzed: Myctophidae (Electrona and Gymnoscopelus), Zoarcidae (Melanostigma), Gempylidae (Paradiplospinus), Paralepididae (Notolepis), and Bathylagidae (Bathylagus) showed no antifreeze activity. Two endemic species captured in the same sampling program did show antifreeze activity: the important pelagic species Pleuragramma antarcticum (Nototheniidae) and the Bathydraconid species Vomeridens infuscipinnus. The absence of AFGPs in the blood of Antarctic oceanic species makes a strong case for temperature exclusion of oceanic fishes in the coastal Antarctic.