The Israeli Journal of Aquaculture - Bamidgeh 54(4), 2002, 173-182

MILT PRODUCTION OF SEA BASS LATES CALCARIFER BLOCH
ADMINISTERED AN ANALOGUE OF
LUTEINIZING HORMONE-RELEASING HORMONE
AND 17α-METHYLTESTOSTERONE


G.V. Hilomen-Garcia¹* , R.B. Baldevarona² and F.Lacanilao¹
1 Aquaculture Department, Southeast Asian Fisheries Development Center, 5021 Tigbauan, Iloilo, Philippines
2 Institute of Aquaculture, University of the Philippines in the Visayas, 5023 Miagao, Iloilo, Philippines

(Received 4.3.02, Accepted 10.4.02)

Key words: hormone, LHRHa, methyltestosterone, milt, sea bass

Abstract

The milt production responses of sexually mature sea bass Lates calcarifer to (D-Ala6, Pro9-Nethylamide) luteinizing hormone-releasing hormone (LHRHa) and 17
α-methyltestosterone injections were examined.

At 24 h after injection of a low dose of LHRHa (20 g/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, spermatocrit, 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 production, 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 g/kg BW). A methyltestosterone injection combined with the LHRHa injection also resulted in a significantly lower sperm count, but the spermatocrit remained comparable to the control group, suggesting 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.

*Corresponding author. E-mail: ghgarcia@aqd.seafdec.org.ph ,fax: +63-33-3351008
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