This study investigated whether culturing age-0 steelhead (Oncorhynchus mykiss) in habitat-enriched rearing tanks, containing a combination of in-water structure, underwater feeders, and overhead cover, affected competitive ability and habitat use compared with juveniles cultured in more conventional vessels. In laboratory tests, steelhead juveniles grown in the enriched tanks socially dominated size-matched competitors grown in conventional tanks. When both treatments were introduced into separate sections of a quasi-natural stream, no differences in growth were found between them. However, when intermixed, fish reared in the enriched tanks grew at a higher rate than conventionally reared competitors, suggesting greater competitive ability of juveniles grown in the enriched tanks. Visual isolation and defensible food resources in combination in the enriched tanks were considered as the primary factors causing the observed competitive asymmetries. Steelhead juveniles from the two rearing environments exhibited very similar use of woody structure in the quasi-natural stream, both in the presence and in the absence of mutual competition. Rearing steelhead in more naturalistic environments could result in hatchery fish that behave and integrate into the postrelease (natural) environment in a manner more similar to wild fish.

The use of captive broodstocks is becoming more frequently employed as the number of species facing endangerment or extinction throughout the world increases. Efforts to rebuild the endangered Snake River sockeye salmon, Oncorhynchus nerka, population have been ongoing for over a decade, but the use of microsatellite data to develop inbreeding avoidance matrices is a more recent component to the program. This study used known genealogical relationships among sockeye salmon offspring to test four different pairwise relatedness estimators and a maximum-likelihood (M-L) relatedness estimator. The goal of this study was to develop a breeding strategy with these estimators that would minimize the loss of genetic diversity, minimize inbreeding, and determine how returning anadromous adults are incorporated into the broodstock along with full-term hatchery adults. Results of this study indicated that both the M xy and R QG estimators had the lowest Type II error rates and the M-L and R R estimators had the lowest Type I error rates. An approach that utilizes a combination of estimators may provide the most valuable information for managers. We recommend that the M-L and R R methods be used to rank the genetic importance of returning adults and the M xy or R QG estimators be used to determine which fish to pair for spawning. This approach provides for the best genetic management of this captive, endangered population and should be generally applicable to the genetic management of other endangered stocks with no pedigree.

We investigated competition among newly emerged fry from captive-reared and wild female coho salmon Oncorhynchus kisutch by conducting dominance challenges and growth and survival experiments in laboratory stream channels. Newly emerged fry from captive-reared females won a significant majority (72.7%) of dyadic dominance challenges against fry from wild females. In a growth and survival experiment conducted from emergence to 30 d postemergence, fewer captive brood fry died of apparent starvation when food was limited than wild fry, further suggesting a competitive advantage for the captive brood fry. All fry used in the study were paternal half-sibs, so observed differences between captive brood and wild fry were attributed to the maternal parent. We hypothesize that fry coloration resulting from differences in egg color between wild and captive-reared females may have influenced the observed competitive asymmetries. If so, such differences might be ameliorated by changes in husbandry practices such as providing more natural diets.

The use of diets supplemented with live food lo increase the postrelease foraging ability of hatchery-reared fall chinook salmon Oncorhynchus tshawytscha was investigated. Replicate groups of fry were reared in six 2.4-m-diarneter circular tanks and fed one of two diets. Fish in three tanks received a commercially available pelletized diet; fish in the other three tanks were given the opportunity to forage on natural live prey (mysids, mosquito larvae, chironomid larvae, and daphnia) prior lo their daily ration of pellets. Foraging by individual lish was observed in special 200-L tanks, and fish conditioned to live food fed on twice as many familiar prey (chironomids) and novel prey (mayfly larvae) as unconditioned fish fed on. This suggests that diets supplemented with live food can be used to increase the postrelease foraging effectiveness of hatchery-reared chinook salmon.