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Relative growth and survival of offspring from matings of hatchery and wild Deschutes River (Oregon) summer steelhead trout, Salmo gairdneri, were measured to determine if hatchery fish differ genetically from wild fish in traits that can affect the stock–recruitment relationship of wild populations. Sections of four natural streams and a hatchery pond were each stocked with genetically marked (lactate dehydrogenase genotypes) eyed eggs or unfed swim-up fry from each of three matings: hatchery × hatchery (HH), hatchery × wild (HW), and wild × wild (WW). In streams, WW fish had the highest survival and HW fish the highest growth rates when significant differences were found; in the hatchery pond, HH fish had the highest survival and growth rates. The hatchery fish were genetically different from wild fish and when they interbreed with wild fish may reduce the number of smolts produced. Hatchery procedures can be modified to reduce the genetic differences between hatchery and wild fish.

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Sockeye salmon (Oncorhynchus nerka) introduced into Lake Washington in the 1930s and 1940s now spawn at several different sites and over a period of more than 3 months. To test for evolutionary divergence within this derived lineage, embryos that would have incubated in different habitats (Cedar River or Pleasure Point Beach) or at different times (October, November, or December in the Cedar River) were reared in the laboratory at 5, 9, and 12.5°C. Some developmental variation mirrored predictions of adaptive divergence: (i) survival at 12.5°C was highest for embryos most likely to experience such temperatures in the wild (Early Cedar), (ii) development rate was fastest for progeny of late spawners (Late Cedar), and (iii) yolk conversion efficiency was matched to natural incubation temperatures. These patterns likely had a genetic basis because they were observed in a common environment and could not be attributed to differences in egg size. The absolute magnitude of divergence in development rates was moderate (Late Cedar embryos emerged only 6 days earlier at 9°C) and some predictions regarding development rates were not supported. Nonetheless our results provide evidence of adaptive divergence in only 9-14 generations.Résumé : Le saumon rouge (Oncorhynchus nerka) introduit dans le lac Washington dans les années 30 et 40 fraye maintenant à plusieurs endroits différents et sur une période de plus de 3 mois. Pour établir s'il y a eu divergence évolutionnaire chez cette lignée dérivée, des embryons qui auraient été incubés dans des habitats différents (rivière Cedar ou plage Pleasure Point) et à des périodes différentes (octobre, novembre ou décembre dans la rivière Cedar) ont été élevés en laboratoire à 5, 9 et 12,5°C. Certaines variations dans le développement correspondaient aux prédictions de divergence adaptative, notamment : (i) la survie à 12,5°C était plus élevée chez les embryons les plus susceptibles d'être exposés à une telle température dans le milieu d'origine (ponte hâtive, rivière Cedar), (ii) le taux de développement était plus élevé chez la progéniture des géniteurs tardifs (ponte tardive, rivière Cedar) et (iii) l'efficacité de conversion du vitellus concordait avec les températures d'incubation dans le milieu. Ces tendances sont probablement d'origine génétique parce qu'elles ont été observées dans un environnement commun et ne pouvaient être attribuées à des différences dans la taille des oeufs. L'ampleur absolue de la divergence au plan des taux de développement était modérée (les embryons tardifs de la rivière Cedar ne sont sortis de l'oeuf que 6 jours plus tôt à 9°C) et certaines prédictions concernant le taux de développement n'ont pas été confirmées. Néanmoins nos résultats fournissent l'évidence de la divergence adaptive dans seulement les neuf à quatorze générations. [Traduit par la Rédaction]Can.

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Strontium isotope and Sr/Ca ratios measured in situ by ion microprobe along radial transects of otoliths of juvenile chinook salmon (Oncorhynchus tshawytscha) vary between watersheds with contrasting geology. Otoliths from ocean-type chinook from Skagit River estuary, Washington, had prehatch regions with 87Sr/86Sr ratios of ~0.709, suggesting a maternally inherited marine signature, extensive fresh water growth zones with 87Sr/86Sr ratios similar to those of the Skagit River at ~0.705, and marine-like 87Sr/86Sr ratios near their edges. Otoliths from stream-type chinook from central Idaho had prehatch 87Sr/86Sr ratios ≥0.711, indicating that a maternal marine Sr isotopic signature is not preserved after the ~1000- to 1400-km migration from the Pacific Ocean. 87Sr/86Sr ratios in the outer portions of otoliths from these Idaho juveniles were similar to those of their respective streams (~0.708–0.722). For Skagit juveniles, fresh water growth was marked by small decreases in otolith Sr/Ca, with increases in Sr/Ca corresponding to increases in 87Sr/86Sr with migration into salt water. Otoliths of Idaho fish had Sr/Ca radial variation patterns that record seasonal fluctuation in ambient water Sr/Ca ratios. The ion microprobe's ability to measure both 87Sr/86Sr and Sr/Ca ratios of otoliths at high spatial resolution in situ provides a new tool for studies of fish rearing and migration.

Distance transferred from the natal stream was negatively related to recovery rate (recruits per gram of juveniles released) for hatchery-reared coho salmon Oncorhynchus kisutch. This relation, which reflects the important influence of genetic adaptation and genetic differences among stocks on recovery rates and survival, should be useful in deciding whether or not to transfer fish.

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