EFFECTS OF SUBZERO TEMPERATURES AND TRAWLING STRESS ON SERUM OSMOLALITY TN THE WINTER FLOUNDER PSEUDOPLEURONECTES AMERICANUS

¹ Department of Biology, Yale University, New Haven, Connecticut

1. The average serum osmolality of winter flounder, Pseudopleuronectes americanus, acclimated in the laboratory to -1° C (386 mOsm/liter) was not significantly different from the serum osmolality of fish at 15° C (389 mOsm/liter).

2. Winter flounder survived temperatures as low as -1.5° C in a supercooled state. When ice crystals were present in the sea water at -1.8° C, the fish froze and died due to nucleation of the supercooled blood.

3. The serum osmolality of freshly caught flounder increased significantly with time after capture (up to six hours) and was significantly higher than the serum osmolality of laboratory acclimated fish at the same temperature.

4. A previous account of "antifreeze" formation in the winter flounder at low temperatures was probably due to an increased serum osmolality produced by trawling stress during capture.