Polar Biol (1985) 4:45-52 © Springer-Verlag 1985 Adaptations for Cryopelagic Life in the Antarctic Notothenioid Fish

fish Pagothenia borchgrevinki lives near the undersur-face of the sea ice in McMurdo Sound, Antarctica. When compared to closely related benthic species (especially Trematomus bernacchii), Pagothenia exhibited substantial morphological differences in a variety of organ systems. The values of the fineness ratio and the indices of trunk shape and flatness suggested streamlin-ing and drag reduction, adaptations to life in the water column. Pagothenia also lacked substrate contact adaptations in the pelvic and anal fins. Silvery reflective layers (strata argentea) beneath the skin and in the iris and choroid of the eye provided camouflage when Pago-thenia were viewed against a background of platelet ice. The retina had many cones indicating the eye was adapted to both diurnal and nocturnal vision. During the austral spring Pagothenia fed exclusively on nektonic or-ganisms near the ice-water interface. Dietary diversity was low; copepods and amphipods were the most fre-quently occurring taxa. In conclusion, Pagothenia p-pear specialized for life in the water column