Hatchery Steelhead Trout Research Articles

Offspring of first-generation hatchery steelhead trout (Oncorhynchus mykiss) grow faster in the hatchery than offspring of wild fish, but survive worse in the wild: Possible mechanisms for inadvertent domestication and fitness loss in hatchery salmon.

Salmonid fish raised in hatcheries often have lower fitness (number of returning adult offspring) than wild fish when both spawn in the wild. Body size at release from hatcheries is positively correlated with survival at sea. So one explanation for reduced fitness is that hatcheries inadvertently select for trait values that enhance growth rate under the unnatural environment of a hatchery, but that are maladaptive in the wild environment. A simple prediction of this hypothesis is that juveniles of hatchery origin should grow more quickly than fish of wild origin under hatchery conditions, but should have lower survival under wild conditions. We tested that hypothesis using multiple full sibling families of steelhead (Oncorhynchus mykiss) that were spawned using either two wild parents (WxW) or two first-generation hatchery (HxH) parents. Offspring from all the families were grown together under hatchery conditions and under semi-natural conditions in artificial streams. HxH families grew significantly faster in the hatchery, but had significantly lower survival in the streams. That we see this tradeoff after only a single generation of selection suggests that the traits involved are under very strong selection. We also considered one possible alteration to the hatchery environment that might reduce the intensity of selection among families in size at release. Here we tested whether reducing the fat content of hatchery feed would reduce the variance among families in body size. Although fish raised under a low-fat diet were slightly smaller, the variation among families in final size was unchanged. Thus, there is no evidence that reducing the fat content of hatchery feed would reduce the opportunity for selection among families on size at release.

Growth, survivorship, and juvenile physiology of triploid steelhead (Oncorhynchus mykiss)

Induced triploidy typically causes sterility in teleost fishes, and has therefore been proposed as a tool to manage genetic risks that farmed and hatchery-produced salmon pose to wild populations. Application of this technology for aquaculture has been challenged by inferior growth, survivorship and, in the case of free-ranging anadromous salmonids, relatively low numbers of adult returns. There is little information on whether or not triploidy affects the physiological development of juvenile salmonids in ways that impair their ability to grow, imprint on natal waters, survive, and return from the ocean as adults. In this study we pressure treated fertilized eggs to produce two cohorts of triploid hatchery steelhead trout (i.e., anadromous Oncorhynchus mykiss). We calculated survivorship through early life stages, and measured gill ATPase and plasma thyroxine (T4) for yearling triploids and their full-sibling diploid controls. We found no clear pattern of difference between diploid and triploid steelhead for the biomarkers of smoltification T4 or ATPase. After a year of freshwater rearing, we transferred 448 tagged treatment and control fish to a saltwater tank, and tracked their growth and survivorship for over 15 months. Diploids outperformed triploids in growth and, by the end of our study, survivorship of diploids (72%) was more than twice that of triploids (35%). Our findings suggest that inferior growth and survivorship of triploids in saltwater seriously challenge the application of this technology for free-ranging steelhead and, by extension, Pacific salmon. Additional research is needed to identify and offset the causal mechanisms underpinning triploid attrition during saltwater rearing.

Rapid discovery of SNPs that differentiate hatchery steelhead trout from ESA-listed natural-origin steelhead trout using a 57K SNP array

Natural-origin steelhead trout (Oncorhynchus mykiss (Walbaum, 1792)) in the Pacific Northwest, USA, are threatened by a number of factors including habitat destruction, disease, decline in marine survival, and a potential erosion of genetic viability due to introgression from hatchery strains. Our major goal was to use a recently developed SNP array containing ∼57 000 SNPs to identify a subset of SNPs that differentiate hatchery and natural-origin populations. We analyzed 35 765 polymorphic SNPs in nine populations of steelhead trout sampled from Puget Sound, Washington, USA. We then conducted two outlier tests and found 360 loci that were candidates for divergent selection between hatchery and natural-origin populations (mean FCT = 0.29, maximum = 0.65) and 595 SNPs that were candidates for selection among natural-origin populations (mean FST = 0.25, maximum = 0.51). Comparisons with a linkage map revealed that two chromosomes (Omy05 and Omy25) contained significantly more outliers than other chromosomes, suggesting that regions on Omy05 and Omy25 may be of adaptive significance. Our results highlight several advantages of the 57 000 SNP array as a tool for population and conservation genomics studies.

A single generation of domestication heritably alters the expression of hundreds of genes.

The genetic underpinnings associated with the earliest stages of plant and animal domestication have remained elusive. Because a genome-wide response to selection can take many generations, the earliest detectable changes associated with domestication may first manifest as heritable changes to global patterns of gene expression. Here, to test this hypothesis, we measured differential gene expression in the offspring of wild and first-generation hatchery steelhead trout (Oncorhynchus mykiss) reared in a common environment. Remarkably, we find that there were 723 genes differentially expressed between the two groups of offspring. Reciprocal crosses reveal that the differentially expressed genes could not be explained by maternal effects or by chance differences in the background levels of gene expression among unrelated families. Gene-enrichment analyses reveal that adaptation to the novel hatchery environment involved responses in wound healing, immunity and metabolism. These findings suggest that the earliest stages of domestication may involve adaptation to highly crowded conditions.

Grandfathering in a new era of parentage analysis

The advent of DNA fingerprinting and microsatellite techniques has revolutionized the way in which we investigate genetic pedigrees in the wild (Pemberton 2008). With large and often incomplete data sets consisting of hundreds to thousands of individuals over multiple generations becoming commonplace, new methods in parentage analysis are being developed to rise to the next generation of questions and challenges. In this issue, Christie et al. (2011) provide a simple yet elegant solution to the problem of identifying missing parents and assessing hybrid fitness in a mixed population of wild and hatchery steelhead trout (Oncorhynchus mykiss) where not all individuals can be sampled effectively. They develop a new method of grandparent analysis where parental genotypes can be reconstructed using data from candidate grandparent crosses and F2 offspring genotypes, allowing for new explorations of hybridization, migration and gene flow in wild populations.

Comparisons between hatchery and wild steelhead trout (Oncorhynchus mykiss) smolts: physiology and habitat use

Hatchery steelhead trout (Oncorhynchus mykiss) smolts, progeny of a newly founded native origin broodstock, were released into Abernathy Creek, Washington, in 2003 and 2004. After release, saltwater tolerance, gill Na+,K+-ATPase activity, and habitat use were compared. A subsample of hatchery and wild steelhead trout were implanted with 23 mm passive integrated transponder (PIT) tags each year. PIT-tagged migrants were used for physiological comparisons. Hatchery fish were significantly larger than wild fish. Hatchery migrants expressed significantly lower levels of gill Na+,K+-ATPase activity than wild migrants. After a 24 h seawater challenge, hatchery migrants had significantly higher plasma osmolality and [Na+] than wild migrants. Microhabitat use of PIT-tagged hatchery and wild individuals in a control (wild fish only) and effect (hatchery and wild fish) site were compared before and after the introduction of hatchery fish. No difference was detected in hatchery and wild smolt habitat use. Wild fish did not change their habitat use after the introduction of hatchery fish. Although hatchery and wild fish differed in smolt physiology, differences in short-term use of freshwater habitat were not detected, and hatchery fish did not appear to displace wild fish.

Comparisons of Run Timing, Spatial Distribution, and Length of Wild and Newly Established Hatchery Populations of Steelhead in Forks Creek, Washington

In Washington State, the approach to management of wild and hatchery steelhead trout Oncorhynchus mykiss has been to separate the timing of return and spawning by the two groups through selective breeding for early timing in hatchery fish. However, overlap in timing and spatial distribution could permit genetic and ecological interactions. To evaluate this management approach, we compared the timing, spatial distribution, and size of adult steelhead in the wild and newly established hatchery populations of Forks Creek, Washington. Hatchery fish tended to return and spawn about 3 months before wild fish but there was some temporal overlap. Radio-tracking indicated that the spatial distributions of the populations overlapped considerably, permitting interbreeding and ecological interactions. However, the hatchery fish tended to stay closer to the hatchery, consistent with olfactory imprinting on the hatchery's water supply. Wild females were larger than hatchery females (median fork lengths were 670 and 644 mm, respectively), and wild males and females varied more in length than did hatchery fish of the same sex. In the first year in which naturally spawned offspring of hatchery fish might have returned, we observed a marked increase in early-returning unmarked (i.e., naturally spawned) adults, suggesting that some hatchery fish spawned successfully in the creek.