Some characteristics of freezing avoidance in two osmerids, rainbow smelt and capelin

• Published in: Journal of Fish Biology
• Main Authors: Raymond, J. A., Hassel, A.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2000
• Subjects: Barents Sea
• Online Access: http://dx.doi.org/10.1111/j.1095-8649.2000.tb02240.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1095-8649.2000.tb02240.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1095-8649.2000.tb02240.x

Winter‐acclimatised rainbow smelt Osmerus mordax have elevated levels of glycerol and trimethylamine oxide (TMAO), and a protein antifreeze, all of which are lost in summer. No seasonal differences were found in glycerol‐3‐P‐dehydrogenase, glycerol‐3‐phosphatase and glutamate dehydrogenase, which are involved in the synthesis of glycerol or its precursors. Although glycerol production requires NADH, no large seasonal differences were found in the activities of glucose‐6‐P‐dehydrogenase and 6‐phosphogluconate dehydrogenase (pentose phosphate pathway), malate dehydrogenase and aspartate aminotransferase (malate‐aspartate shuttle) or in the NAD : NADH ratio. Thus, other regulatory mechanisms must be involved. Capelin Mallotus villosus collected from mid water in the Barents Sea in September (water temperatures +0·4 to −1·6°C) had only negligible amounts of glycerol, and no protein antifreeze, although serum TMAO levels (44 mm) were unusually high for a teleost. Capelin appear to avoid freezing largely by avoiding water layers with temperatures below their body freezing point, and by occasional supercooling.