Lack of species-specific primer effects of odours from female Atlantic salmon, Salmo salar, and brown trout, Salmo trutta

We exposed, in two successive spawning seasons, individually placed precoci ous male Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) parr to odour stimuli (ovarian fluid and urine mix) from ovulated conspecific or heterospecific anadromous females. Atlantic salmon parr had significantly higher plasma concentrations of the hormones 17 alpha,20 beta-dihydroxy-4-p regnen-3-one (17,20 beta-P), 11-ketotestosterone (11-KT) and testosterone ( T) after exposure to odours from conspecific females or from brown trout fe males compared to parr exposed to a control solution (0.9% NaCl). We did no t observe any significant differences between the hormone levels in salmon parr exposed to the two female odours. The salmon parr exposed to conspecif ic odours had significantly higher volumes of strippable milt compared to t he controls, but we did not find any significant differences when comparing the effect of the two female odours. Brown trout parr had significantly hi gher plasma 17,20 beta-P levels following exposure to heterospecific female odours compared to control males, but there was no significant difference between males exposed to the different female odours. We did not observe an y significant differences in plasma levels of T and 11-KT and in milt volum es between exposed and control trout. Taken together, the results from both tested species indicate that the potency of heterospecific stimuli in stim ulating increased plasma sex steroid hormone levels in male parr was as str ong as stimuli from conspecific females. The results are discussed in conne ction to observed hybridisation between the two sympatric species.