GAMETE RIPENING AND HORMONAL CORRELATES IN 3 STRAINS OF LAKE TROUT

In our 2-year laboratory study of hatchery-reared adult lake trout Sal velinus namaycush of the Seneca Lake, Marquette (Lake Superior Lean), and Jenny Lake strains, we compared gamete ripening times and changes in plasma concentrations of seven hormones. If interstrain differences in these traits were found, such differences might help explain the a pparent failure of stocked fish of these strains to develop large, nat urally reproducing populations in the Great Lakes. The complex tempora l changes in plasma hormone levels that occur during sexual maturation in lake trout have not been previously described. We detected little evidence of temporal isolation that would prevent interbreeding among the three strains. Strain had no effect on ovulation date (OD) in eith er year. Strain did not affect spermiation onset date (SOD) in year 1 but did in year 2, when the mean SOD of Jenny Lake males was earlier t han that of Seneca Lake males but not different from that of Marquette males. Hormonal data were normalized around ODs for individual female s and SODs for individual males. In females, estradiol-17beta (E2) was highest 8 weeks before the OD; the highest testosterone (T) level occ urred 6 weeks before the OD, and the next highest level occurred simul taneously with the highest level of 11-ketotestosterone (11-KT) 2 week s before the OD. Plasma levels of 17alpha-hydroxy-20beta-dihydroproges terone (DHP) peaked 1 week before the OD, then abruptly declined immed iately after. Cortisol (F), triiodothyronine (T3), and thyroxine (T4) were highly variable, but F was the only hormone that showed no trend with week in either year. In males, plasma E2 levels were highest 3 we eks before the SOD, highest levels of T and of 11-KT occurred simultan eously 2 weeks after the SOD, and DHP peaked 5 weeks after the SOD and 3 weeks after the highest levels of T and 11-KT. As in females, plasm a levels of F, T3, and T4 were highly variable, and F was the only hor mone that showed no trend with week in either year. Strain had no effe ct on any hormones in females and only on T and F in males. The lack o f pronounced interstrain differences in gamete ripening dates and repr oductive endocrinology and the similarity of the temporal patterns and relative concentrations of hormones to those reported for other salmo nids suggest nothing unusual or dysfunctional about these reproductive traits that would impede lake trout rehabilitation in the Great Lakes .