The influence of temperature on sex determination in sockeye salmon Oncorhynchus nerka

Thermolability in phenotypic expression of sex was examined in hime salmon, a land-locked type of sockeye salmon Oncorhynchus nerka, which is a commercially valuable species in cold-water lakes of Japan and is expected to have good potential for aquaculture. Eyed-eggs or alevins of genetically all-female fish were subjected to high temperature. Water temperature was raised from 9 to 18 degreesC (1) in the middle of the eyed-egg stage, 42 days post-fertilization (dpf); (2) just before starting of hatch, 57 dpf, (3) just after completion of hatch, 78 dpf, or (4) 20 days thereafter, 98 dpf, and kept constant at 18 degreesC until 63 days after emergence of alevins. Fewer survivals were observed when the temperature was raised early in development. The survival rate in the earliest treatment decreased below 5% at 105 dpf Observation of gonads at 335 to 456 dpf and 733 dpf revealed that 12 of 14 fish (85.7%) exposed to high temperature on and after 57 dpf exhibited a sex change to phenotypic males. Proportions of sex reversal from the genetical female to the phenotypic male decreased contrary to the survival rates as the temperature treatment started later. Sockeye salmon proved to exhibit thermolability in phenotypic expression of sex, and the temperature-sensitive window was demonstrated to exist in the early life stages on and after 57 dpf, which appears to conform with the exogenous androgen-sensitive window. The new technique through temperature control shown in the present study should contribute to producing all-female populations of this species in a safe, simple, environmental friendly, and acceptable manner. (C) 2004 Elsevier B.V. All rights reserved.