CONSEQUENCES OF FISH INTRODUCTION IN THE ABSENCE OF REPRODUCTIVE ISOLATION - INTEREST AND LIMITS OF THE EXPERIMENTAL APPROACH

Stocking generally results in artificial secondary contact and introgr ession between differentiated conspecific populations. The consequence of such introgressions on the genetic and phenotypic variation in wil d stocks is Bn important concern of population genetics and fisheries management. Introgression can be studied directly on natural populatio ns, but the comparison of the fitness of artificial crosses under expe rimental conditions offers an interesting alternative approach. In thi s paper, we report data on growth performance and reproductive success of first and second generation crosses between a domesticated stock a nd a wild Mediterranean population of brown trout (Nei's standard gene tic distance between the two taxa = 0.10). Our results did not reveal any genomic incompatibility between the two taxa. They support the ide a that selective effects are weak or non-existent in introgressed Medi terranean populations. In such conditions, low and temporary gene flow between distinct geographic entities could be beneficial to natural p opulations, and might be artificially established provided that it is compatible with the conservation of the genetic resources of the speci es. These recommendations hold for other species under similar circums tances.