Abstract
To determine the factors that may contribute to the poor survival of triploid (3n) rainbow trout (Oncorhynchus mykiss) in lake stocking programs, we compared the physiology and responses to environmental challenges of four wild strains and one domestic strain of diploid (2n) and 3n juvenile rainbow trout. Over four successive years, wild trout were caught from nature, spawned, and progeny were reared in a hatchery along with hatchery-bred domestic trout. Offspring of each strain were raised for up to 12 months as both 2n and 3n, and growth rate, critical swimming speed, routine oxygen consumption rate, critical oxygen tensions, thermal tolerance, and hypoxia tolerance were assessed in a laboratory setting. Cohorts of the 2008, 2009, and 2010 wild strains were also stocked into two experimental lakes and recaptured as adults using traps and fyke nets in 2011 for laboratory analysis. In the juvenile trout, the only measure of performance to show a consistent difference between 2n and 3n individuals across all strains was hypoxia tolerance, where 3n trout had a shorter time to loss of equilibrium (LOE) at 16 Torr than their 2n counterparts, but this effect was not seen in adult, lake-reared trout. Strain had a significant effect on specific growth rate, critical swimming speed (Ucrit), and time to LOE in hypoxia, although the effects of strain on these variables was not consistent from year to year. Overall, this study suggests that poorer hypoxia tolerance in 3n trout compared with 2n trout may be a contributing factor to the higher lake stocking mortalities in 3n trout. Resume : Afin de cerner les facteurs qui pourraient expliquer la faible survie des truites arc-en-ciel (Oncorhynchus mykiss) triploides (3n) dans le cadre de programmes d’empoissonnement de lacs, nous avons compare la physiologie et les reactions a des defis ambiants de quatre lignees sauvages et d’une lignee domestique de truites arc-en-ciel diploides (2n) et 3n juveniles. Durant quatre annees consecutives, des truites sauvages ont ete capturees en milieu naturel et reproduites, et leur progeniture a ete elevee en aleviniere avec des truites domestiques issues d’aleviniere. La progeniture de chaque lignee a ete elevee pendant une periode allant jusqu’a 12 mois sous forme tant de 2n que de 3n, et le taux de croissance, la vitesse critique de nage (Ucrit), le taux de consommation d’oxygene courant, les tensions d’oxygene critiques, la tolerance a la chaleur et la tolerance a l’hypoxie ont ete evalues en laboratoire. Des cohortes des lignees sauvages de 2008, 2009 et 2010 ont egalement ete empoissonnees dans deux lacs experimentaux et recapturees une fois adultes a l’aide de pieges et de verveux en 2011, pour analyse en laboratoire. Chez les truites juveniles, la seulemesure de la performance quimontre une difference coherente entre les individus 2n et 3n pour toutes les lignees est la tolerance a l’hypoxie, les truites 3n etant caracterisees par une plus courte periode avant la perte d’equilibre a 16 torr que leurs homologues 2n. Cet effet n’est toutefois pas observe chez les truites adultes elevees en lac. La lignee avait une incidence significative sur le taux de croissance specifique, l’Ucrit et la periode avant la perte d’equilibre en hypoxie, bien que les effets de la lignee sur ces variables ne fussent pas uniformes d’une annee a l’autre. Globalement, l’etude indiquerait que la plus faible tolerance a l’hypoxie des truites 3n comparativement aux truites 2n pourrait etre un facteur qui participe aux taux de mortalite plus eleves des truites 3n empoissonnees dans des lacs. [Traduit par la Redaction]
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More From: Canadian Journal of Fisheries and Aquatic Sciences
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