EFFECTS OF AROMATASE INHIBITORS ON REPRODUCTION IN MALE 3-SPINED STICKLEBACKS, GASTEROSTEUS-ACULEATUS, EXPOSED TO LONG AND SHORT PHOTOPERIODS

Three-spined stickleback, Gasterosteus aculeatus, males were implanted with Silastic capsules filled with different aromatase inhibitors; 1, 4,6-androstatriene-3,17-dione or the non-steroidal CGS16949 A, 4-(5,6, 7,8-tetrahydrimidazol [1,5-a]pyridin-5-yl) benzonitrile monohydrochlor ide or empty capsules. The fish were then exposed to long or short pho toperiod. Under the long photoperiod most fish in all treatments displ ayed a hypertrophied kidney (a secondary sexual character in stickleba cks) and completed, quiescent spermatogenesis, similar as in the natur al spawning period. Under the short photoperiod the controls had unsti mulated kidneys and an active spermatogenesis, whereas the males impla nted with both aromatase inhibitors had stimulated kidneys, though not to the extent as in the long photoperiod, and completed, quiescent sp ermatogenesis. These findings suggest that aromatization is of importa nce for the inhibitory effects of short photoperiod on reproduction in the stickleback.