Hormonal changes in male white bass (Morone chrysops) and evaluation of milt quality after treatment with a sustained-release GnRHa delivery system

TitleHormonal changes in male white bass (Morone chrysops) and evaluation of milt quality after treatment with a sustained-release GnRHa delivery system
Publication TypeJournal Article
Year of Publication1997
AuthorsMylonas, CC, Gissis A, Magnus Y, Zohar Y
JournalAquaculture
Volume153
Issue3-4
Pages301 - 311
KeywordsGnRH, GtH, Morone, Sex steroids, Sperm quality, Spermiation, White bass
Abstract

Captive white bass, (Morone chrysops) were exposed to an increase in temperature and treated with a gonadotropin-releasing hormone agonist (GnRHa) delivery system during the spermiation period. Circulating levels of various reproductive hormones, and milt production and quality were examined before and after GnRHa treatment. Circulating levels of gonadotropin II (GtH II) prior to GnRHa treatment were below the assay detection limit (0.4 ng ml -1), while mean (±SEM) plasma levels of 17α,20β-dihydroxy-4-pregnen-3-one (17,20β-P) were 0.09 ± 0.03 ng ml -1 testosterone (T) levels were 0,79 ± 0.11 ng ml -1 and 11-ketotestosterone (11-KT) levels were 1.7 ± 0.3 ng ml -1. Treatment with the GnRHa delivery system induced significant increases in plasma GtH 11 and 17,20β-P after 7 days, whereas T and 11-KT were unaffected. Plasma 17α,20β,21-trihydroxy-4-pregnen-3-one (17,20β,21-P) remained unchanged during the experiment with a mean of 0.55 ± 0.05 ng ml -1. Mean total expressible milt increased significantly after treatment with the GnRHa delivery system, from 2.0 ± 0.1 ml kg -1 body weight on day 0 to 3.6 ± 0.5 ml kg -1 on day 7. Milt production remained constant in saline-injected control fish and averaged 2.1 ± 0.2 ml kg -1. Sperm density, motility and fertilization percentage of total inseminated eggs did not differ between milt from GnRHa- and saline-injected fish, and averaged 52 ± 2 x 10 9 spermatozoa ml -1, 50 ± 4% motile spermatozoa and 60 ± 5% fertilized eggs, respectively. These results demonstrate the effectiveness of sustained GnRHa treatment in enhancing mill production in white bass, without negatively affecting mill quality. It is assumed that enhancement of milt production is caused by high circulating GtH II levels, via the action of 17.20β-P.

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