Repeat sexual maturation of precocious male chinook salmon (Oncorhynchus tshawytscha) transferred to seawater

Abstract

Precocious sexual maturation in salmonid parr occurs under both wild and culture conditions. We investigated the possibility of repeat maturation 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 salt water (29–30 ppt) until September 1990. The precocious parr were significantly larger than the controls from March to July and there were no differences in relative growth rate between the groups throughout the study. Total mortalities were 45.7 and 5.9% for precocious and control fish, respectively. All of the precocious, but none of the control fish, produced milt in March in fresh water. None of the fish produced milt soon after the transfer to salt water in June, but all precocious fish and 18.8% of the controls produced milt in September. There were no significant differences in the average plasma concentrations of Na+, Cl−, and cortisol between groups in September, suggesting that both precocious parr and control groups were saltwater competent. These data demonstrate that male precocious chinook salmon parr have the physiological capability to mature more than once in seawater.