Individual condition, standard metabolic rate, and rearing temperature influence steelhead and rainbow trout (Oncorhynchus mykiss) life histories

Abstract

We reared juvenile Oncorhychus mykiss with low and high standard metabolic rates (SMR) under alternative thermal regimes to determine how these proximate factors influence life histories in a partially migratory salmonid fish. High SMR significantly decreased rates of freshwater maturation and increased rates of smoltification in females, but not males, after 1 year of rearing. Warmer water temperatures significantly decreased rates of freshwater maturation and increased rates of smoltification in both sexes. Variation in individual growth influenced the probability of adopting anadromy or freshwater residency as life histories, but produced paradoxical results. Individuals with the highest growth performance within their respective temperature treatments had a higher probability of freshwater maturation, but warmer temperatures decreased freshwater maturation despite significantly increasing somatic growth. Whole-body lipid content was significantly lower for fish reared in the warm temperature treatment, which may explain the decreased probability of freshwater maturation for individuals exposed to warmer temperatures. Our results indicate that changes in somatic growth induced by altered thermal regimes can influence the relationship between body size and the probability of maturation. Accordingly, somatic growth may not be a robust predictor of shifts in the prevalence of anadromy and residency in partially migratory salmonids when compared across thermal regimes.Résumé : Nous avons élevé des truites arc-en-ciel (Oncorhynchus mykiss) juvéniles caractérisées par des taux métaboliques standards (TMS) faibles et élevés dans différents régimes thermiques afin de déterminer l'influence de ces facteurs sur les cycles biologiques d'un salmonidé partiellement migrateur. Des TMS élevés se sont traduits par une réduction significative des taux de maturation en eau douce et une augmentation des taux de smoltification des femelles, mais non des mâles, après un an d'élevage. Des températures d'eau plus chaudes entraînaient une réduction significative des taux de maturation en eau douce et une augmentation des taux de smoltification des deux sexes. Les variations de la croissance individuelle ont eu une influence sur la probabilité d'adoption de l'anadromie ou de la résidence en eau douce comme types de cycle biologique, produisant toutefois des résultats paradoxaux. Une probabilité accrue de maturation en eau douce était associée aux individus présentant les plus fortes performances de croissance pour un traitement thermique donné, mais les températures plus chaudes, tout en accélérant de manière significative la croissance somatique, entraînaient une réduction de la maturation en eau douce. Le contenu lipidique corporel était significativement plus faible chez les poissons élevés à plus haute température, ce qui pourrait expliquer la plus faible probabilité de maturation en eau douce pour les individus exposés à des températures plus élevées. Nos résultats indiquent que les modifications de la croissance somatique provoq...

Anadromy and residency in steelhead and rainbow trout (Oncorhynchus mykiss): a review of the processes and patterns

“…Offspring from the above-waterfall resident population described earlier also produced significant numbers of smolts and returning anadromous adults despite over 70 years of complete selection against migration (see also Hayes et al 2012;. Likewise, freshwater maturation persists in many, if not all, hatchery steelhead trout stocks after decades of selectively breeding only anadromous adults (Christie et al 2011;Sharpe et al 2007;Sloat and Reeves 2014). Otolith microchemistry revealed that anadromous kelts in the Yakima River basin, Washington, had resident mothers 7% and 20% of the time in each of 2 years of study (Courter et al 2013).…”

“…"Steelhead" and "rainbow trout" are the common North American names for anadromous and freshwater resident life history forms of O. mykiss, respectively, whereas both forms are known as "mykizha" in Russia. Anadromous and resident forms are often sympatric, commonly interbreed, and their offspring may adopt either form (Christie et al 2011;Courter et al 2013;Sloat and Reeves 2014). The balance of life histories can vary, with some populations supporting more residents and others more anadromous individuals (e.g., .…”

“…For example, greater life history diversity in O. mykiss spreads mortality risk over space and time, thereby dampening population fluctuations and increasing resiliency to environmental variability (Moore et al 2014). Further, resident males mating with anadromous females (McMillan et al 2007) and the contribution of anadromous offspring from residents and vice-versa (Christie et al 2011;Courter et al 2013;Sloat and Reeves 2014) offer important avenues for buffering genetic and demographic stochasticity that are much less available to other Pacific salmonines . Declines in the anadromous component of O. mykiss populations in the United States, Canada, and Russia have motivated an increased interest in exploring the factors shaping anadromy and residency, especially as changing climate conditions and anthropogenic activities alter the fitness of these different forms (Benjamin et al 2013;Satterthwaite et al 2010).…”

“…First, because most studies on anadromy and residency in O. mykiss are recent, there is an opportunity to summarize the most influential processes and identify knowledge gaps to help guide future research and monitoring. Second, O. mykiss inhabit the broadest latitudinal range of environments of any salmonine (Behnke 2002), and the environmental variation may provide clues about which habitat factors affect anadromy and residency (Benjamin et al 2013;McMillan et al 2012;Sloat and Reeves 2014), which is especially relevant given the need for understanding the implications of climate change. Third, though genetics (e.g., Nichols et al 2008) and individual condition early in life (e.g., McMillan et al 2012) influence anadromy and residency in O. mykiss as they do with other salmonines (e.g., Simpson 1992), O. mykiss are arguably the most complex of the partially anadromous salmonines.…”

“…Third, though genetics (e.g., Nichols et al 2008) and individual condition early in life (e.g., McMillan et al 2012) influence anadromy and residency in O. mykiss as they do with other salmonines (e.g., Simpson 1992), O. mykiss are arguably the most complex of the partially anadromous salmonines. Thus, they may provide additional insights into life history expression that are observed rarely in Atlantic salmon, such as resident maturation by relatively small, young females (Sloat 2013;Sloat and Reeves 2014). Fourth, correlations between individual condition and life history patterns are not always consistent, and the reasons for such differences have not been fully explored.…”