Absence of seasonal changes in reproductive function of cultured Atlantic salmon migrating into a Canadian river

Abstract

Cultured Atlantic salmon (Salvo s&r) that escaped from sea cages and migrated into the Magaguadavic River, New Brunswick, often showed no external signs of sexual maturation over the period 1992-1996. The sequential changes in plasma testosterone (T), 1 I-ketotestosterone (1 I-KT), and 17l.Gestradiol (E2) were determined in escaped cultured salmon in 19941996 and in wild Atlantic salmon in 1996 to evaluate reproductive status before, during, and after the spawning period. T in males and females, 1 I-KT in males, and E2 in females increased from basal levels in summer to peak values just before spawning in late autumn in all wild salmon. In contrast, there was an absence of change in gonadal steroids from basal levels either during or after the spawning period in the majority (85%) of escaped cultured salmon, indicating that these fish would not spawn later during the year of entry into fresh water. However, 11% of cultured fish were males with steroid profiles that showed a maturation synchronous with that of wild females, indicating that some interbreeding could occur. In 1996, almost half of these cultured males were precociously mature post-smelts. 0 1997 International Council for the Exploration of the Sea