Sperm trait differences between wild and farmed Chinook salmon (Oncorhynchus tshawytscha)
The expansion of salmon aquaculture, coupled with fish escaping from those sites, has raised concerns about the possible impacts of escaped farmed fish on wild fish populations. The potential for hybridization through reproductive interactions between escaped farmed and wild salmon can have significant impacts on the fitness and genetic composition of the natural population. Reproductive success of farmed male salmon in the wild will depend on their ability to compete for mates; however, it will also depend on their relative sperm performance, given that sperm competition is known to contribute to salmonid reproductive success. Farming practices, including the hormonal sex-reversal of females to create homogametic (XX) males, may have effects on sperm traits in salmon. We therefore analyzed sperm traits of XX farmed, XY farmed and wild Chinook salmon males during the spawning season. No significant difference was found between XX and XY farmed males for all sperm traits, except sperm density, which was significantly higher in XY males than XX males. XX and XY farmed males had significantly higher sperm motility and sperm velocity compared to wild males. In addition, wild males had lower sperm longevity and sperm density compared to farmed males. Our results indicate that farming practices may lead to increased sperm performance in Chinook salmon males. While we did not evaluate reproductive success resulting from spawning interactions in the wild, our results do highlight the potential for substantial introgression resulting from male-male competition between farmed and wild Chinook salmon in the wild. (c) 2012 Elsevier B.V. All rights reserved.
Lehnert, Sarah J.; Heath, Daniel D.; and Pitcher, Trevor E.. (2012). Sperm trait differences between wild and farmed Chinook salmon (Oncorhynchus tshawytscha). Aquaculture, 344, 242-247.