Sperm competition and fertilization success of Atlantic halibut (Hippoglossus hippoglossus L.)

Abstract Sperm competition trials were conducted to study the fertilization ability of sperm from four Atlantic halibut ( Hippoglossus hippoglossus L.) males. Sperm from four males were mixed using equal number or equal volume of sperm from each of the males to fertilize eggs from two females. The proportions of larvae sired by the different males were quantified using DNA microsatellite analyzes. Larvae sired by Male 2 dominated the offspring in the trials; this male sired 79% and 78% of the DNA-analyzed offspring of two females. Reducing the number of sperm cells to below 10 5 did not significantly alter the relative proportion of offspring sired by the different males. Male 2 provided 25 and 27% of the total sperm in experiments with equal volumes and equal numbers of sperm, respectively. However, Male 2 provided 47% to 50% of the motile spermatozoa in the mixtures. Furthermore, Male 2 also had the highest sperm velocity (115.7 µm/s). Motility-related sperm traits may partly explain why offspring from Male 2 dominated the larvae. In both control and experimental groups, fertilization rates were high (> 90%) when sufficient numbers (10 5 –10 6 ) of spermatozoa per egg were used, and the fertilization success did not depend on whether sperm from one, or from a mixture of four males were used. Uncritical use of pooled sperm from different males during fertilization may cause unexpected results with only a few parents represented in an offspring population. Mixing sperm from different males without exact knowledge of sperm motility parameters may ultimately lead to low genetic variability, inbreeding, and strains with low fitness.