Does Dominant Fish Sperm Guarantee Reproductive Success?

The saying all is fair in love and war may not necessarily apply in the case of the Arctic char. A cold-water fish that populates alpine lakes, the Arctic char's sperm swims at different speeds in different fluids. Sperm speed is determined by whether the fish is submissive or dominant.

Norwegian researchers published the study in Frontiers in Ecology and Evolution showed that while numerous species of fish congregate at mating grounds to release eggs and sperm, conditions are hardly equal. Dominant males guard and court female fish, making sure subordinate males won't be able to come close.

This behavior allows dominant male fish to release their sperm closer to the females and time their release at the exact moment females release a mix of eggs and ovarian fluid into the water. Since fertilization is an external process, the sperm from subordinate males still has a chance to fertilize the released eggs but only if they are able to actually get close enough.

Torvald B. Egeland of Nord University led the research, working with colleagues from both Nord University and the University of Tromsø. Based on formerly published studies, reproductive competition is conducted at a cellular level. Egeland's recent study shows that the sperm of dominant and subordinate Arctic char swim at different speeds in different fluids. To be specific, dominant Arctic char produce sperm that swim faster in diluted ovarian fluid. Subordinate males, on the other hand, produce sperm that swim faster in water.

Given the position of dominant fish that are usually closer to the burst of eggs and ovarian fluid released by the female, their sperm will be able to swim faster and gain significant reproductive advantage. The subordinate males release sperm that moves faster in water and this significantly makes up for how far they are from the female fish. Egeland and his team are still in the process of determining whether these adaptations result in reproductive success of either dominant or submissive male Arctic chars.

"The challenge is to conduct an experiment that closely mimics the situation under spawning. In order to thoroughly study these adaptations, we need a setup where we can control the distance between where the sperm is released and the ovarian fluid surrounding the eggs, and at the same time we also need to be able to control the effects of water dilution," explained Egeland.