The spermiation period in the rainbow trout ( Salmo gairdneri ) . Plasma gonadotropin and androgen levels , sperm production and biochemical changes in the seminal fluid

Plasma immunoreactive t-GTH and androgens, sperm production and biochemical changes in seminal fluid were studied during the spermiation period in rainbow trout. The volume of sperm collected by hand-stripping was very low (< 0.1 ml) at the onset of spermiation, increased slowly during the next 4 weeks and sharply thereafter. Plasma t-GTH was high (6 ng/mi) at the onset and then decreased ; the sharp rise in sperm production started when circulating androgens had reached maximum values. In a second phase (b-12 weeks), the elevation in sperm production was strongly correlated wth plasma t-GTH, while plasma androgens fluctuated. Spermatocrit did not vary significantly during the period studied so that increased sperm production corresponded to an elevation in spermatozoal production. During spermiation Na + ionic concentration in the seminal fluid increased sharply and that of K+ only slightly. Total protein in the seminal fluid decreased significantly after 8 weeks.