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Characterizing the stage of maturity most receptive to an acute LHRH-analogue therapy for inducing milkfish (Chanos chanos) to spawn

1988; Elsevier BV; Volume: 74; Issue: 1-2 Linguagem: Inglês

10.1016/0044-8486(88)90094-4

1873-5622

Clyde S. Tamaru, C.-S. Lee, C.D. Kelley, J.E. Banno, Phyllis Y. Ha, Katsumi Aida, Isao Hanyu,

Fish Ecology and Management Studies

This paper discusses two factors critical to the effective use of acute LHRH-a therapy in the induced spawning of milkfish: (1) the stage of maturity at which female milkfish respond to a single injection of LHRH-a, and (2) the minimum effective dosage of LHRH-a. In terms of maturation stage, serial ovarian biopsies were obtained from individuals undergoing chronic LHRH-a plus 17α-methyltestosterone therapy. In vivo changes in the growth rate and size frequency distribution of oocytes were monitored as were profiles of testosterone and estradiol-17β that accompany egg growth, using radioimmunoassay procedures. The stage of maturity most receptive to an acute LHRH-a therapy was characterized by possession of oocytes averaging 750 μm or more and a unimodal size distribution. If there was a bimodal distribution, the average diameter of the smaller eggs should not exceed 400 μm. The in vivo pattern of oocyte growth was found to be consistent between and within individuals. A predictive model of egg growth, i.e. egg size = 359.077 + 28.796 (days) − 0.475 (days2), was formulated from the current data and validated with growth rates from a 1985 study. Changes in serum levels of estradiol-17β and testosterone were highly correlated with egg growth. The endocrine profile that occurs at the stage of maturity most receptive to inducing milkfish to spawn is discussed. The minimum effective dosage of LHRH-a ranged between 1 and 5 μg/kg body weight. Within the range of dosages tested (1–65 μg/kg body weight), there was no significant effect on fecundity, fertilization rate, spawned egg diameter, or number of spawns in which fertilization was obtained. Dosages administered to the male milkfish (20–65 μg/kg body weight) were not correlated with the occurrence of fertilized spawns.