Milt Production Of Sea Bass Lates Calcarifer Bloch Administered An Analogue Of Luteinizing Hormone-Releasing Hormone And 17α-Methyltestosterone

Abstract

The milt production responses of sexually mature sea bass Lates calcarifer to (D-Ala6, Pro9-N- ethylamide) luteinizing hormone-releasing hormone (LHRHa) and 17α-methyltestosterone injec- tions were examined. At 24 h after injection of a low dose of LHRHa (20 μg/kg BW), the sperm count decreased significantly compared to saline-treated fish, but it returned to pre-treatment levels 48 h after injection, suggesting a possible hydration of the milt. Other milt parameters (milt volume, sper- matocrit, sperm production) in LHRHa-treated fish did not vary from their controls at 24 or 48 h after injection but the overall pattern suggested a reduction in milt viscosity. Total expressible milt and spermatozoa collected over the 48-h experiment was approximately three-fold higher in LHRHa-injected fish than in saline-injected fish, indicating a stimulation of spermatozoa produc- tion, not merely milt dilution due to hydration. In a second experiment, sperm count and spermatocrit were significantly lower than those of saline-injected fish at 17 and 48 h after a single injection of a high dose of LHRHa (80 μg/kg BW). A methyltestosterone injection combined with the LHRHa injection also resulted in a significant- ly lower sperm count, but the spermatocrit remained comparable to the control group, suggest- ing a suppression of the LHRHa-induced milt hydration response. Results demonstrate that LHRHa stimulates milt hydration and spermatozoa production in milting sea bass and that a simultaneous methyltestosterone injection partially suppresses this response.