Physiological Characterization of Hatchery-Origin Juvenile SteelheadOncorhynchus mykissAdopting Divergent Life-History Strategies

Abstract

Smoltification by juvenile Pacific salmonids has been described as a developmental conflict whereby individuals face several life-history decisions. Smoltification occurs as a result of interactions between organismal condition and environmental cues, although some fish may forgo ocean migration and remain in freshwater streams for some time (residualize). We compared the physiological profiles of steelhead that were actively migrating to the ocean (migratory fish) and those that remained in fresh water (residuals) for at least a period of between 2 wk and 3 mo after release from a hatchery facility. In addition, we investigated the physiological characterization of residuals that further differentiated into precocial freshwater residents or parr that will either precocially mature in fresh water or migrate to the ocean in the future. Residuals had higher condition factors and gonadosomatic index than migratory fish and were characterized as less prepared for saltwater due to low levels of gill Na+,K+-ATPase activity and Na+,K+-ATPase α1b-subunit expression. Residuals tended to be males with the highest condition factors. Sex-specific differences are probably reflective of male fish adopting an alternative life-history strategy foregoing outmigration as a result of condition at the time of release. Collection of residuals throughout the fall suggested that residual hatchery fish further diversify into precocially mature fish that will presumably attempt to spawn without ever migrating to the ocean or into parr that will precocially mature or migrate in a future year.

Estimating Abundance and Life History Characteristics of Threatened Wild Snake River Steelhead Stocks by Using Genetic Stock Identification

“…This is not surprising because anadromy should benefit females more than males (Hendry et al 2004). Sex ratios skewed toward females have been observed in adult steelhead populations throughout the species' range, including California, Alaska, the Columbia River basin, and the Kamchatka Peninsula in Russia (Savvaitova et al 1997;Hendry et al 2004;Christie et al 2011;Hanson et al 2011). Female-biased sex ratios in steelhead have been attributed to two separate life history behaviors: the predominance of residualization among males and the tendency of anadromous females to spawn more than once (Savvaitova et al 1997;McMillan et al 2007).…”

Divergent immunity and energetic programs in the gills of migratory and resident Oncorhynchus mykiss

“…The majority of migratory fish from this location leave the system within 13 days after release from the facility (Hanson et al . ).…”

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

“…This has also been shown for O. mykiss. Hanson et al (2011) found that steelhead smolts released from a hatchery that did not migrate had higher condition factors but were shorter than smolts at the time of release (Table 2). This is relevant because Beakes et al (2010) found in 1 of 2 years that future O. mykiss smolts had higher condition factors than future non-smolts almost a year prior to smolting, but that by NovemberDecember non-smolts had greater condition factors (Table 2), perhaps because smolts became more fusiform in shape as time of smolting approached (Jonsson 1985).…”

“…Washington; Hanson et al 2011 Early male maturation in fresh water positively correlated with size and lipid content 9 months prior to the spawning season Oregon; McMillan et al 2012 Females with faster growth and higher lipids matured as residents, while males with faster growth matured as residents; residents had lower metabolic costs.…”