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Marine Ecology Progress Series

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MEPS 375:219-228 (2009)  -  DOI:

Sperm characteristics and competitive ability in farmed and wild cod

Jon E. Skjæraasen1,*, Ian Mayer1,5, Justin J. Meager1, Geir Rudolfsen2, Ørjan Karlsen3, Thomas Haugland2, Oddmund Kleven4

1Department of Biology, University of Bergen, 5020 Bergen, Norway
2Department of Evolution and Ecology, University of Tromsø, 9037 Tromsø, Norway
3Institute of Marine Research, Austevoll Research Station, 5392 Storebø, Norway
4National Centre for Biosystematics, Natural History Museum, University of Oslo, 0318 Oslo, Norway
5Present address: Norwegian School of Veterinary Science, 0033 Oslo, Norway

ABSTRACT: The development of cod aquaculture has raised concerns about its effect on wild stocks. One risk is hybridisation between escapees and wild cod, causing genetic introgression, and, potentially, fitness depressions in wild populations. The potential for hybridisation depends on escapee success in mating competition with wild fish. Cod have a complex mating system, with males likely to adopt either dominant or sub-dominant roles, the latter typically achieving reproductive success through sperm competition. Studies on salmonids indicate that domesticated males predominantly adopt sub-dominant roles. We therefore analysed sperm characteristics of wild and farmed cod Gadus morhua L. around the onset and end of the natural spawning season. Wild and farmed males were also paired in in vitro crosses to assess reproductive success in sperm competition. In the early spawning season, wild males had higher sperm velocity, percentages of motile and progressive cells, and spermatocrit. Sperm velocity was the main determinant of fertilisation success in in vitro sperm competition and, accordingly, wild males had higher reproductive success. At the end of spawning, the percentages of motile or progressive cells and spermatocrit were similar between wild and farmed males, but wild males maintained higher sperm velocity. Our results indicate that farmed males have limited reproductive success in sperm competition with wild male cod. This presumably reduces the risk of genetic introgression from escapees. We hypothesise that impaired sperm quality and lower reproductive fitness of farmed cod are due to inhibition of the full behavioural repertoire, lack of social structure under culture conditions, and/or nutritional deficiencies.

KEY WORDS: Gadus morhua · Escapees · Sperm competition · Mating system · Reproductive roles

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Cite this article as: Skjæraasen JE, Mayer I, Meager JJ, Rudolfsen G, Karlsen Ø, Haugland T, Kleven O (2009) Sperm characteristics and competitive ability in farmed and wild cod. Mar Ecol Prog Ser 375:219-228.

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