Freeze susceptibility in haddock (Melanogrammus aeglefinus)

Haddock (Melanogrammus aeglefinus) is a promising new species for aquaculture in Eastern Canada. Because haddock aquaculture could involve overwintering of fish in sea cages in icy near-short: areas, haddock freeze resistance was studied. Measurements were done on the blood of wild haddock collected during the winter from Georges and St. Pierre Banks as well as from cultured haddock originating from Northeast Bank in the Bay of Fundy. Freezing points were within the normal range for teleost blood, suggesting no freeze resistance adaptations. Glycerol in blood samples from Georges Bank and from most cultured haddock was not above normal physiological levels whereas St. Pierre Bank and Sandy Cove fish showed elevated glycerol levels. However, glycerol in the latter group was far lower than amounts required to depress the blood freezing point to a safe level in icy seawater. Thermal hysteresis measurements revealed no antifreeze protein (AFP) activity in any of the samples. However, ice crystal morphology revealed small amounts of AFP in a haddock sample collected in sub-zero seawater. The haddock antifreeze differed from the antifreeze glycoproteins (AFGPs) of other gadids in that it was active in the presence of peanut lectin and inactivated by EDTA. Neither the glycerol levels nor the trace level of AFP shown here would be sufficient to protect this species from freezing in icy seawater during winter. (C) 2000 Elsevier Science B.V. All rights reserved.