REPEAT SEXUAL-MATURATION OF PRECOCIOUS MALE CHINOOK SALMON (ONCORHYNCHUS-TSHAWYTSCHA) TRANSFERRED TO SEAWATER

Precocious sexual maturation in salmonid parr occurs under both wild a nd culture conditions. We investigated the possibility of repeat matur ation in precocious chinook salmon parr from the Nicola River, British Columbia. Precocious and immature (control) yearling parr were reared in fresh water from March 1990 to mid-June, and then transferred to s alt water (29-30 ppt) until September 1990. The precocious parr were s ignificantly larger than the controls from March to July and there wer e no differences in relative growth rate between the groups throughout the study. Total mortalities were 45.7 and 5.9% for precocious and co ntrol fish, respectively. All of the precocious, but none of the contr ol fish, produced milt in March in fresh water. None of the fish produ ced milt soon after the transfer to salt water in June, but all precoc ious fish and 18.8% of the controls produced milt in September. There were no significant differences in the average plasma concentrations o f Na+, Cl-, and cortisol between groups in September, suggesting that both precocious parr and control groups were salt-water competent. The se data demonstrate that male precocious chinook salmon parr have the physiological capability to mature more than once in seawater.