Cryopreservation of Arctic charr, Salvelinus alpinus (L.), semen in various extenders and in three sizes of straw

Cryopreservation of Arctic charr semen was investigated using 3 diluents (0.3 M glucose, 0.3 M glucose with 0.011 M KCl and 0.137 M NaCl, 0.011 M KCl, 0.004 M Na2HPO4 with 7.5 g/litre L- alpha -lecithin adjusted to pH 7.5) 3 cryoprotectants [10% dimethyl sulphoxide (DMSO), 10% dimethylacetamide (DMA) or 20% glycerol] and 3 sizes of straw. The 3 diluents and 3 cryoprotectants were combined, resulting in 9 extenders. One part semen was added to 3 parts extender, and motility was evaluated to assess the toxicity of 6 of the extenders. Semen in 9 extenders was frozen in 0.5-ml straws using liquid nitrogen vapour. Semen extended in 0.3 M glucose and each of the cryoprotectants was frozen in 0.5-ml, 1.7-ml (flat) or 2.5-ml straws. The freezing rate in each size of straw was measured. Fertility trials were conducted to determine the post-thaw viability of the frozen semen. The motility of activated spermatozoa was higher in the DMA and DMSO extenders than in the glycerol extender. For the trial using 0.5-ml straws, post-thaw fertility results were higher for all extenders containing DMSO, or 0.3 M glucose and DMA, than for all other combinations of diluent and cryoprotectant. For the straw size comparison, the highest fertility was obtained with 1.7-ml straws using either DMSO or DMA and with 2.5-ml straws using DMSO. For all cryopreservation trials, fertility was low for extenders containing glycerol..