Evidence of Successful Natural Reproduction between Brown Trout and Mature Male Atlantic Salmon Parr

Abstract

Hybridization between Atlantic salmon Salmo salar and brown trout S. trutta is frequently reported, and the role of mature male Atlantic salmon parr has been suspected but never proven. Salmon fry were stocked into a headwater tributary stream of the Connecticut River, where no adult salmon are present. The stream has a self‐sustaining population of brown trout. Enzyme electrophoresis revealed the presence of one hybrid (0.81% of the sampled population). The maternal species was identified as brown trout; therefore, the only possibility for the male parent was that it was a mature male Atlantic salmon parr. This is the first direct evidence of parr producing hybrid offspring in a totally natural setting and in the absence of any sea‐return salmon.

Interspecific barriers between salmonids when hybridisation is due to sneak mating

“…Hybrids were obtained from brown trout females and sneaking mature male parr. This confirms by first time that alternative male mating behaviour allows interspecific hybridisation in salmonids, as suggested by Elo et al (1995), Jansson and Ost (1997) and Gephard et al (2000) from field observations, and by Olsén et al (2000) from the potency of heterospecific stimuli in endocrine responses in male parr. Similar results were obtained in other taxa: insects (Nomakuchi and Higashi, 1996), anuran (Gergus et al, 1999) and also other fish (Neat, 2001).…”

“…However, they should exist because mature parr are very abundant in these rivers (Héland and Dumas, 1994;Nicieza and Brañ a, 1995;Utrilla and Lobon-Cervia, 1999). The existence of this type of hybrids in the wild has been proved unambiguously in North American rivers (Gephard et al, 2000). Our results show that, although in a very small proportion (around 1%), these hybrids can survive until dispersion from nest.…”

“…In hybrids from European rivers the mother was Atlantic salmon in some cases (Youngson et al, 1992(Youngson et al, , 1993Garcia-Vazquez et al, 2001) and brown trout in others (Hartley, 1996;Jansson and Ost, 1997). American wild hybrids were reported to be the product of a cross between female brown trout and male Atlantic salmon (McGowan and Davidson, 1992a;Gephard et al, 2000).…”

“…Between species male parasitic spawning has been described in Axoclinus triplefin blenny fish (Neat, 2001). Hybrids issued from brown trout mother were sampled in river areas where sneaker Atlantic salmon males are present (Elo et al, 1995;Jansson and Ost, 1997;Gephard et al, 2000). This suggests that the sneaking behaviour of small Atlantic salmon males is responsible for interspecific hybridisation between Atlantic salmon and brown trout.…”

Brown Trout-Salmon Hybrids in Bulgarian Rivers are not a Red Herring

“…Control over stocking and restocking, however, is somewhat relaxed and the specificities of different types of sites used for stocking are often underestimated, thus the presence of interspecies hybrids cannot be ruled out. Existence of viable post-F1 salmonid hybrids has been demonstrated before (1,5). The current policy of stocking Bulgarian waters with salmonids might have to be reviewed and revised if and when needed, to the benefit of preserving the genetic diversity of free-living populations and avoiding introgression between species.…”