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Age of maturation in many salmonid species is phenotypically plastic and dependent on exceeding a genetically set threshold in growth, often described as a probabilistic maturation reaction norm (PMRN). Hatchery supplementation programs for Chinook salmon (Oncorhynchus tshawytscha) in the Pacific Northwest US have been developed to minimize differences between hatchery and wild fish by integrating natural-origin adults into broodstock, potentially affecting PMRNs. We raised fish from 10 Chinook salmon stocks with variable levels of natural-origin integration in a common garden environment to explore potential genetic variation in PMRNs for precocious male maturation as age 2 minijacks. Proportion minijacks varied [approximately equal to] 10-fold (0.043 to 0.443) and the PMRN [W.sub.P50] (predicted weight at 50% maturation) varied by [approximately equal to] 18 g (24.1 to 41.7 g). The propensity for minijack maturation was generally higher in stocks with higher levels of natural-origin integration. These findings demonstrate the effect of genotype by environment interactions on life history of salmonids and the need for stock-specific tailoring of rearing regimes to regulate differences between hatchery and wild fish, when wild fish are used in broodstocks. L'age a la maturation chez de nombreuses especes de salmonides est un caractere plastique sur le plan phenotypique et depend du depassement d'un seuil de croissance fixe par la genetique, souvent decrit comme une norme de reaction de maturation probabiliste (NRMP). Des programmes de supplementation avec des individus issus d'ecloseries visant le saumon chinook (Oncorhynchus tshawytscha) dans la region du Pacific Northwest des Etats-Unis ont ete conqus pour minimiser les differences entre poissons sauvages et d'ecloseries, en incorporant des adultes d'origine naturelle au stock de geniteurs, ce qui peut avoir une incidence sur les NRMP. Nous avons eleve des poissons issus de 10 stocks de saumons chinooks caracterises par differents degres d'integration d'individus d'origine naturelle dans un milieu de type jardin commun afin d'examiner les variations genetiques potentielles des NRMP pour la maturation de petits males precoces de 2 ans. La proportion de petits males precoces varie sur environ un ordre de grandeur (de 0,043 a 0,443) et la fourchette de valeurs de la NRMP [W.sub.P50] (masse predite a 50 % de la maturation) est de [approximately equal to] 18 g (de 24,1 a 41,7 g). La propension a la maturation precoce de petits males est generalement plus grande dans les stocks caracterises par une plus grande incorporation d'individus d'origine naturelle. Ces constatations font ressortir l'effet des interactions du genotype et du milieu sur le cycle biologique des salmonides et la necessite d'adapter les regimes d'elevage aux stocks pour reguler les differences entre les poissons sauvages et d'ecloseries dans les cas ou des poissons sauvages sont utilises dans des stocks de geniteurs. [Traduit par la Redaction], Introduction Managing gene flow between cultured and naturally rearing salmon stocks is an important issue facing fisheries managers in many regions. Cultured salmon have been directly or haphazardly selected for [...]

Abstract--We evaluated 4 potential indices obtained by nonlethal sampling for use in determining nutritional state and short-term growth rate in postsmolt Atlantic salmon (Salmo salary, the ratio of RNA to [...]

We examined postprandial changes in circulating growth hormone (GH), insulin, insulin-like growth factor (IGF)-I, and IGF-binding proteins (IGFBPs) in yearling coho salmon under different feeding regimes. Fish were initially fasted for 1 day, 1 wk, or 3 wk. Fasted fish were then fed, and blood was collected at 4-h intervals over 26 h. After the various periods of fasting, basal levels of insulin were relatively constant, whereas those of IGF-I, IGFBPs and GH changed in proportion to the duration of the fast. A single meal caused a rapid, large increase in the circulating insulin levels, but the degree of the increase was influenced by the fasting period. IGF-I showed a moderate increase 2 h after the meal but only in the regularly fed fish. Plasma levels of 41-kDa IGFBP were increased in all groups within 6 h after the single meal. The fasting period did not influence the response of 41-kDa IGFBP to the meal. IGFBP-1 and GH decreased after the meal to the same extent among groups regardless of the fasting period. The present study shows that insulin and IGF-I respond differently to long (weeks)- and short (hours)-term nutritional changes in salmon; insulin maintains its basal level but changes acutely in response to food intake, whereas IGF-I adjusts its basal levels to the long-term nutritional status and is less responsive to acute nutritional input. IGFBPs maintain their sensitivity to food intake, even after prolonged fasting, suggesting their critical role in the nutritional regulation of salmon growth. fasting; refeeding; growth; metabolism

Abstract: An experiment was performed to determine the relative effects of photoperiod at emergence and growth rate on smolting pattern and early male maturation rate in Sacramento River (California, USA) [...]

Water temperature can have a profound influence on development and distribution of aquatic species. Salmon are particularly vulnerable to temperature changes because their reproductive and early development life phases are spent in freshwater river systems where temperature fluctuates widely both daily and seasonally. Flow regulation downstream of dams can also cause temperature regime changes, which in turn may spur local adaptation of early life-history traits. In a common garden laboratory incubation experiment, we exposed spring Chinook salmon ( Oncorhynchus tshawytscha) embryos to four temperature regimes: warm stable, cold stable, daily variation and below dam. We found that fry from warmer thermal regimes emerged earlier than those from colder regimes both in terms of calendar date and temperature units and that warmer temperatures caused fry to emerge less developed. There was also a significant effect of family on both emergence timing and development level at emergence. By combining measurements of physiological and behavioural traits at emergence and interpreting them within a reaction norm framework, we can better understand which populations might be more vulnerable to altered thermal regimes. [ABSTRACT FROM AUTHOR]