Supportive breeding with subsequent stocking is an important long-term conservation tool for sustaining harvestable populations and genetic diversity in wild fish populations.

I understand that the Challenger Institute of Technology was successfully breeding several popular fish species for wild stock enhancement. Their activity have since ceased largely due to the argument that the genetics of the wild stock would be adversely affected. But I think that if it is carefully managed, genetic diversity can still be maintained. Check out this article for more information.

Aquaculture
Volume 357, Number 3 (August 2012)
	Interbreeding of genetically distinct native brown trout (Salmo trutta) populations designates offspring fitness
	Authors:	Jens Wollebæk, Knut H. Røed, Åge Brabrand, Jan Heggenes
	Author Affiliations:	no affiliations available
	Source:	Aquaculture, Volume 357, Number 3 (August 2012)
	Page Numbers:	158 – 168
	Available Full Text:	Full Text: Subscription Required to view full text Format: PDF Size: Unknown Location: Publisher’s Site Authentication: Publisher’s Site
	Abstract:	Supportive breeding with subsequent stocking is an important long-term conservation tool for sustaining harvestable populations and genetic diversity in wild fish populations. In salmonids, this strategy often implies, inadvertently or for logistic reasons, breeding of a mixture of local populations, which may lead to loss of local adaptation and pose risks to receiving populations. In an alpine lake system in Norway (Pålsbu-Tunhovd), we assessed long-term effects of interbreeding three brown trout (Salmo trutta) populations from separate and environmentally contrasting spawning and recruitment habitats. Using a Bayesian genetic assignment algorithm we compared numeric contributions and genetic and demographic characteristics of wild-born and lake-stocked fish within and across populations. Population contribution by the broodstock was disproportional to the number of surviving and reproductively ready stocked brown trout, indicating higher lifetime survival for brown trout descending from a large river dominated by large fish. Life history selection was further indicated by a discrepancy between observed and expected numbers of adult hybrids, i.e., fewer hybrids suggest negative fitness effects of hybridization. Hence, supportive breeding changed gene frequencies, although reduced genetic variation was not documented in mature stocked brown trout. Post stocking, these fish retained the initial length advantage relative to the fastest-growing wild-born population until the age of ten. Stocked brown trout had similar growth rates regardless of genetic origin, whereas wild-born brown trout growth rates differed among recruitment habitats. Our study in this system indicates that genetic origin determined longevity. Genetics may be a less important determinant for growth rates in lake-stocked than in wild-born brown trout.
	Citation:	Jens Wollebæk, Knut H. Røed, Åge Brabrand, Jan Heggenes . Interbreeding of genetically distinct native brown trout (Salmo trutta) populations designates offspring fitness. Aquaculture, Volume 357, Number 3 (August 2012), pp. 158-168, <http://ejournals.ebsco.com/direct.asp?ArticleID=4178B5BD05DA1236D955&gt;
	URL:	http://ejournals.ebsco.com/direct.asp?ArticleID=4178B5BD05DA1236D955