The presence and quantification of splenic ice in the McMurdo Sound Notothenioid fish, Pagothenia borchgrevinki (Boulenger, 1902)

Survival of some polar fishes is associated with high levels of circulating antifreeze glycoproteins (AFGPs). AFGP prevent ice growth giving rise to thermal hysteresis. The inhibiting action of AFGPs implies that polar fish contain ice to which AFGPs adsorb. Cryopelagic Pagothenia borchgrevinki, inhabiting the ice-laden waters of McMurdo Sound, Antarctica, were assayed for ice and ice was found on skin, gills, in the intestine, and in the spleen. Two methods used to assess the number of ice crystals in spleens gave comparable results (12.1 +/- 1.9 and 22 +/- 3.8 per spleen). Attempts were made to measure the rate of uptake of ice by P. borchgrevinki held in cages immediately beneath the sub-ice platelet layer in McMurdo Sound; uptake was sporadic. Introduction of ice into fish by spray freezing a small patch of the integument resulted in detection of splenic ice after 1 h, illustrating that a mechanism exists for ice transport from the periphery to the spleen. Splenic ice did not seem to be eliminated from fish held in ice-free water at - 1.6 °C for approximately two months. The relatively small number of splenic ice crystals and the slow rate of ice uptake suggest efficient ice barriers exist in P. borchgrevinki.