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Marine Ecology Progress Series

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MEPS 412:247-258 (2010)  -  DOI:

Mating competition between farmed and wild cod Gadus morhua

J. E. Skjæraasen1,*, J. J. Meager1, Ø. Karlsen2, I. Mayer1,3, G. Dahle2, G. Rudolfsen4, A. Fernö1

1Department of Biology, University of Bergen, 5020 Bergen, Norway
2Institute of Marine Research, 5817 Bergen, Norway
3Norwegian School of Veterinary Science, 0033 Oslo, Norway
4Department of Evolution and Ecology, University of Tromsø, 9037 Tromsø, Norway

ABSTRACT: Increasing numbers of hatchery-produced fish entering marine environments has caused concern over potential fitness depressions in wild populations, yet no study has addressed the likelihood of hybridisation between farmed and wild marine fish. Escape rates of Atlantic cod Gadus morhua L. from commercial net pens have been substantial and there is a risk of interbreeding between depleted local coastal populations and escapees. We studied mating competition between farmed and wild cod in 2 mixed spawning groups. In addition to detailed behavioural analysis, we examined a suite of individual male characteristics thought to be associated with male reproductive success, including, for the first time in any ‘naturally’ spawning teleost, sperm motility traits. We found that the expression of reproductive behaviours was similar for both male types (farmed and wild). Males ‘courted’ both sexes, but courtships lasted longer with a female recipient. Both farmed and wild males also directed most female courtships towards farmed females. The frequency of male displays was linked to their steroid levels. Wild males sired 75% of eggs spawned by wild females, but only 48 to 67% of eggs spawned by farmed females. It is likely that wild females rejected farmed males and chose among the wild males based primarily on behavioural cues. Female choice thus appears to be an integral part of the cod mating system. Sperm traits were not associated with overall reproductive success. Our results suggest that hybridisation between farmed escapees and wild cod is likely and that farmed cod may interfere with the natural spawning behaviour of cod.

KEY WORDS: Genetic introgression · Leks · Female choice · Sperm traits · Gadus morhua

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Cite this article as: Skjæraasen JE, Meager JJ, Karlsen Ø, Mayer I, Dahle G, Rudolfsen G, Fernö A (2010) Mating competition between farmed and wild cod Gadus morhua. Mar Ecol Prog Ser 412:247-258.

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