Methanol and Egg Yolk as Cryoprotectants for Atlantic Salmon Spermatozoa

Abstract

The effects of four extenders on the fertilization rates of eggs fertilized with cryopreserved sperm of Atlantic salmon Salmo salar were tested. We used (1) glucose extender (54.04 g glucose/L and 1.7 g KCl/L) with 5% DMSO, (2) glucose extender with 5% DMSO supplemented with 13.3% egg yolk, (3) glucose extender with 10% methanol, and (4) glucose extender with 10% methanol supplemented with 13.3% egg yolk. Fertilization rates, expressed as the percentage of eyed embryos, ranged from 52.7% to 83.5%. Sperm cryopreserved with the glucose extender and 10% methanol supplemented with 13.3% egg yolk yielded significantly higher fertilization rates (83.5%) than did sperm cryopreserved with the other three extenders. Our fertilization rates compare favorably with those observed for eggs from the same year-class fertilized with fresh milt (81.4%) and reared at the White River National Fish Hatchery. The presence of egg yolk in extenders incorporating 10% methanol provided additional protection to salmonid sperm during the freezing and thawing processes and resulted in an increase in survival from 72.9% to 83.5%. However, the cryoprotective effect of egg yolk may be specific to the individual formulation of extenders. In our trials, glucose and 5% DMSO without egg yolk yielded a 66.9% fertilization rate, while glucose and 5% DMSO supplemented with 13.3% egg yolk produced only 52.7% fertilization after cryopreservation.