The effect of sperm to egg ratio and gamete contact time on fertilization success in Atlantic cod Gadus morhua L.

Currently, Atlantic cod (Gadus morhua) is the primary finfish species being developed for aquaculture in North Atlantic waters. Despite the importance of this species, no research has been conducted to assess the effects of sperm density and gamete contact time on egg fertilization. In two separate experiments male and female gametes were crossed using nested factorial designs. For each male–female combination we tested sperm to egg ratios ranging from 1 × 103:1 to 5 × 106:1. We also tested two gamete contact times where sperm and eggs were held in contact with each other for 5 or 30 min. Mixed-model ANOVAs indicated that sperm density and gamete contact time had a significant effect on fertilization success. Below a sperm to egg ratio of 1 × 105:1 fertilization success significantly decreased. Therefore, a standard sperm to egg ratio of 1 × 105 sperm per egg is recommended for fertilization in Atlantic cod. At the 1 × 103:1, 5 × 103:1, and 1 × 104:1 sperm to egg ratios maximum fertilization occurred after 30 min sperm to egg contact time. Gamete contact time was not significant at sperm to egg ratios of 1 × 105:1 and 1 × 106:1. Both the maternal and paternal variance components were significant for fertilization success. This information has important implications for optimizing family production in selective breeding programs, conserving sperm from superior pedigree in genome banks, maximizing the use of available gametes in hatchery or research facilities, and understanding mating success in the wild.