TESTOSTERONE AND 17-BETA-ESTRADIOL PLASMA FLUCTUATIONS THROUGHOUT SPAWNING PERIOD IN MALE AND FEMALE RAINBOW-TROUT, ONCORHYNCHUS-MYKISS (WALBAUM), KEPT UNDER SEVERAL PHOTOPERIOD REGIMES

Plasma levels of testosterone (T) and 17 beta-estradiol (E2) were meas ured in rainbow trout during the course of their first and second spaw ning period. Trout were exposed to normal photoperiod (Group C) and tw o static, artificial light regimes (Group A, 20L:4D from January to 15 May, then 4L:20D; Group B, 4L:20D from March to August, then 20L:4D). Identical patterns of E2 fluctuations were observed in all groups; E2 levels rose from 54 days prior to spawning and kept rising to reach a peak at 18 days prior to spawning, then decreased steadily reaching b asal levels at ovulation. T levels rose from 54 days prior to spawning and peaked 6-8 days prior to spawning and then declined sharply befor e ovulation, reaching basal levels 6-12 days post spawning. T in male trout peaked 12-0 days prior to milt production. No correlation was fo und between the steroids levels and percentage of ovulated and spermia ted fish. No difference was observed in plasma E2 levels carrying ripe or overripe eggs. T and E2 fluctuations were also observed at the pop ulation level (both mature and non-mature fish). These findings suppor t the use of plasma T and E2 levels as an ancilliary predictor index/t ool for the initiation of the spawning period and for the determinatio n of the timing for human intervention (stripping).