Milt production response of the seabass Lates calcarifer (Bloch) to luteinizing hormone releasing hormone analogue and 17 a-methyltestosterone
1994
Garcia, G.H. (Philippines Univ. in the Visayas, Leganes, Iloilo (Philippines). Coll. of Fisheries)
Two measures of sperm density, sperm count, and spermatocrit were highly correlated (r + 0.85). Compared to control, milt volume and the number of spermatozoa collected increased, but sperm count decreased (24 percent at 24 h) after an LHRHa (20/kg body weight) treatment, suggesting a stimulation of spermatozoa production and not merely milt dilution. Further milt dilution (44 percent) was induced by 80 micro g/kg LHRHa (LHRHa80) at 12 h post-treatment but not by 200 micro g/kg MT (MT200) alone. A milt dilution of only 27 percent at 12 h after simultaneous injections of LHRHa80 and MT200 may indicate an inhibitory effect of a high MT dose on the efficacy of LHRHa. Early in the breeding season, a high fertilization capacity (857,800 eggs/kg) of LHRHa80-treated male was obtained only when spawning occurred in less than 12 h after hormone treatment, but no fertilization occurred in 30-36 h post-treatment. During the peak season and when spawning occurred in 30-36 h post-treatment, a low fertilization capacity (79,000 eggs/kg) was observed in one of two LHRHa (40 micro g/kg)-treated male, but none in three LHRHa80-treated males. However, higher fertilization capacities (224,000-410,000 eggs/kg) in two of three males injected 100 micro g/kg MT (MT 100) were obtained. Towards the end of the breeding season, spontaneous milt release, as indicated by fertilization of eggs, occurred only after multiple injections of MT 100. Together, these results indicate that spermatozoa production, milt dilution, and spontaneous milt release can be stimulated by LHRHa or a lot MT dose. The low incidence of fertilization and variability in fertilization capacity of hormone treated seabass may be due to a possible lack of synchrony in the release of gametes
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