Evaluation of milt quality of Atlantic salmon

Abstract Milt was collected individually from 27 Atlantic salmon, and sperm density, sperm motility, milt colour and osmolality, and content of sodium, potassium and glucose of seminal plasma recorded. Milt from each male fertilized samples of around 200 eggs taken from the same pool of eggs. Percentage of eyed-eggs was used as a measure of fertilization rate or milt quality. Large variation among males was observed for this trait. Variation among males for the recorded parameters was medium to high in magnitude. Correlation between sperm density registered by cell counting and spermatocrit was high ( r =0.92). Repeatability was lowest for motility (0.72), and 0.92 or higher for other parameters. Of the parameters studied, sodium content in seminal plasma showed the highest correlation ( r =0.60) to fertilization rate. The remaining variation in fertilization rate could not be explained by any of the other parameters studied. However, all traits except for sperm motility and milt colour showed a significant correlation to fertilization rate. With repeated stripping within season, the sperm density gradually decreased and the sodium/potassium ratio increased, resulting in decreasing fertilization rate.