SPAWNING OF ESCAPED FARMED ATLANTIC SALMON (SALMO-SALAR) - HYBRIDIZATION OF FEMALES WITH BROWN TROUT (SALMO-TRUTTA)

Atlantic salmon (Salmo salar) and F1 hybrids between Atlantic salmon a nd brown trout (Salmo trutta) were distinguished among juvenile salmon ids sampled at emergence from rivers in western and northern Scotland. Hybrids were present in samples obtained from seven of the 16 rivers examined. Salmon fry and hybrid fry that were demonstrably the progeny of female salmon that had escaped from fish farms were identified by detecting the presence of maternal canthaxanthin, a synthetic flesh co lorant, in the juveniles' pigment load. Canthaxanthin was detected in 101 (4%) of the 2350 salmon and eight (35%) of the 23 hybrids examined . The difference in the frequencies of salmon and hybrids carrying can thaxanthin was significant. Escaped female salmon hybridized with trou t more frequently than did wild females.