Hatchery trout being restocked in Pennsylvania.
It turns out that it's not just dogs, cows and chickens that suffer deficiencies when inbred. So too do fish. As Scientific American reports:
Plummeting numbers of several salmon and trout species have conservationists looking more and more to hatcheries — where fish are reared in comfortable captivity and then released into natural bodies of water. But this strategy may hurt wild populations, according to a paper published this week in Biology Letters.
Researchers at Oregon State University (O.S.U.) found that not only do hatchery-raised steelhead—a Pacific trout sharing the same genus, Oncorhynchus, as salmon—produce relatively fewer and weaker offspring once back in a natural environment, but so do their wild-born spawn....
....Araki and his colleagues looked at the Hood River steelhead supplementation program in Oregon and found that trout fry raised by two hatchery-reared parents had just 37 percent of the reproductive success of those with two wild-born parents, even though both sets of offspring were born in wild waters. If the fry had a mix of one wild and one hatchery-raised parent, then it had 87 percent of a pure-bred wild fry’s reproductive fitness.
Scientists are studying the issue, and are not certain the cause for the decline in fecundity, but inbreeding depression in hatchery stock is strongly suspected.