STIMULATORY AND INHIBITORY EFFECTS OF TESTOSTERONE ON TESTES IN ATLANTIC SALMON MALE PARR

Immature 1-year-old Atlantic salmon Sake salar parr were implanted wit h Silastic capsules of different sizes filled with testosterone (T). T estosterone had both positive and negative effects on testicular weigh ts, spermatogenesis and steroidogenesis. The positive effects: higher incidence of males with enlarged gonads, spermiation, and high plasma levels of 11-ketotestosterone (11-KT) and 17,20 beta-dihydroxy-4-pregn en-3-one (17,20 beta-P), were most pronounced in males treated with sm all T capsules. The negative effects: suppression of gonadal developme nt and depressed plasma levels of 11-KT and 17,20 beta-P compared with mature controls, were most evident in fish treated with large T capsu les. (C) 1995 The Fisheries society of the British Isles.