COMPARISON, USING MINISATELLITE DNA PROFILING, OF SECONDARY MALE CONTRIBUTION IN THE FERTILIZATION OF WILD AND RANCHED ATLANTIC SALMON (SALMO-SALAR) OVA

Secondary males, either subdominant adults or, more usually, parr whic h mature in freshwater, are known to successfully fertilise Atlantic s almon (Salmo salar) ova. This study has estimated the reproductive suc cess of such secondary males in redds formed by pairs of wild and sea- ranched adults. Eight wild and 11 ranched redds were sampled from the Burrishoole system, western Ireland, in two consecutive years. Represe ntative samples of fertilised ova were screened at three minisatellite loci to reconstruct the genotypes of putative anadromous parents and to estimate the proportion of eggs fertilised by secondary males. Mult iple paternal genotypes were detected in 18 of the 19 samples, and of the 1484 progeny examined, 593 could not have been derived from the pr imary adult male genotype. The level of secondary male contribution de tected among wild redds from Burrishoole (mean 28.9%) was similar to t hat found in previous published studies. The level among ranched redds was significantly higher (mean 48.2%) (P = 0.042). The difference was greater when data from 1995 were considered done, with the average le vel of secondary male contribution in ranched redds being almost twice that in wild redds. Minimum numbers of secondary males were not signi ficantly different between wild (mean 2.6) and ranched (mean 2.7) redd s.