Research has indicated that salmonids raised in a hatchery and stocked into the wild have lower future survival and reproductive success than wild fish. Understanding whether hatchery rearing practices affect populations after stocking can help to maximize the quality, quantity, and economic value of fish stocked for conservation and recreational purposes. The goal of our study was to test whether and to what extent rearing density affects poststocking survival of Rainbow Trout Oncorhynchus mykiss when stocked into a put-grow-and-take fishery. Rainbow Trout were raised for 3 months in the hatchery at two different densities (high = 51,948–13,072 fish/m3, rearing index 2.0; low = 12,987–3,268 fish/m3, rearing index 0.5). A subset of the fish where PIT-tagged and stocked into Parvin Lake, Red Feather Lakes, Colorado. Recaptures of tagged fish occurred every 2 weeks for the first 2 months post stocking and at 7 and 12 months post stocking. At the time of stocking, there were no statistical differences in Fulton’s condition factor, total length, weight, or hepatosomatic index for each treatment. Recapture data indicated that there was no difference in Fulton’s condition factor and hepatosomatic index after stocking. Apparent poststocking survival was higher for fish raised at low density (mean survival = 2.3%) in the hatchery compared with those raised at high density (mean survival – 0.48%). Our study suggests that rearing density affects fingerling Rainbow Trout poststocking survival. Stocking more fish due to fish being reared at higher densities within the hatchery did not result in more total fish remaining after a year in the lake compared with the low-density treatment. Hatcheries and managers may benefit from raising fish at lower densities in the hatchery. Reduced densities in the hatcheries can lead to reduced costs and a better-quality product, while better poststocking survival could result in increased recruitment and more fish reproducing in the wild.
Dr. Brian Avila Bio
Dr. Brian Avila is an aquatic research scientist at Colorado Parks and Wildlife where his current focus is on using genetics for broodstock management. His work spans whirling disease management, bacterial coldwater disease resistance, Bayesian mark-recapture movement modeling, and genomics. He has 15 years of experience developing and evaluating the production, stocking, and reestablishment success of whirling disease resistant Rainbow Trout strains in both the hatchery and the wild. His research has spurred discussions between hatcheries and managers regarding the wider range of the effects of rearing densities in the hatchery, data collection, and how management decisions are made in the hatchery or with stocking. He is passionate about using complex biological data and bridging the gap between research and management. His current projects are Roundtail Chub genomics and population genetics of wild and hatchery Rainbow Trout broodstocks in Colorado.