NATURAL SELECTION AFTER RELEASE FROM A HATCHERY
LEADS TO DOMESTICATION IN STEELHEAD
Reg Reisenbichler, Steve Rubin, Lisa Wetzel
and Steve Phelps. 2004. Natural selection
after release from a hatchery leads to domestication in steelhead, Oncorhynchus
mykiss. Pages 371-383 In K.M. Leber, H.L. Blankenship, S. Kitada, and T.
Svåsand [editors] Stock Enhancement and Sea Ranching: developments, pitfalls,
and opportunities. 2nd edition. Blackwell Science Ltd, Oxford.
Abstract: Genetic theory and data suggest that sea ranching of
anadromous salmonids (Oncorhynchus spp. And Salmo spp.) results in domestication
(increased fitness in the hatchery program) accompanied by a loss of fitness
for natural propagation. We tested for
genetic differences in growth, survival, and downstream migration of hatchery
and wild steelhead (O. mykiss) reared
together in a hatchery. We found little
or no difference in survival during rearing but substantial differences in
growth and subsequent downstream migration.
Intense natural selection after release from the hatchery favored fish
that had performed well (e.g. grew fast) in the hatchery. This selection in the natural environment
genetically changes (domesticates) the population because at least some of the
performance traits are heritable.
Domestication should improve the economic efficiency for producing adult
hatchery fish but compromise conservation of wild populations when hatchery
fish interbreed with wild fish.
Quotes from the text: “In this chapter we focus on
domestication because it may limit effective supplementation where the goal is
to increase the numbers of fish spawning naturally and thereby increase the
number of naturally produced adults in the subsequent generation. Supplementation with hatchery fish has been
identified as an important tool for increasing wild populations of anadromous
salmonids in North America’s Pacific Northwest.
“Hatchery environments for Pacific salmonids differ
radically from natural environments in the kinds and amounts of food, habitat structure
and complexity, population density, predators, and community structure. Population genetics theory predicts that, if
additive genetic variation exists for traits with different fitness in the two
environments, a population will change genetically as it adapts to the novel
environment of the hatchery.