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Luteinizing hormone and sexual steroid plasma levels after treatment of European sea bass with sustained‐release delivery systems for gonadotropin‐releasing hormone analogue
Author(s) -
Mañanós E.,
Carrillo M.,
Sorbera L. A.,
Mylonas C. C.,
Asturiano J. F.,
Bayarri M. J.,
Zohar Y.,
Zanuy S.
Publication year - 2002
Publication title -
journal of fish biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.672
H-Index - 115
eISSN - 1095-8649
pISSN - 0022-1112
DOI - 10.1111/j.1095-8649.2002.tb00283.x
Subject(s) - milt , dicentrarchus , endocrinology , medicine , luteinizing hormone , sea bass , biology , hormone , testosterone (patch) , gonadotropin , stimulation , fish <actinopterygii> , fishery
Spermiating male European sea bass Dicentrarchus labrax were treated with gonadotropin‐releasing hormone agonists (GnRHa), either a GnRHa injection (IN; 25 μg kg −1 body mass) or one of three types of controlled‐release GnRHa‐delivery systems: fast release implants (EVAc; 1OO μg kg −1 ), slow release implants (EVSL; lOO μg kg −1 ) and slow release microspheres (MC; 50 μg kg −1 ). Luteinizing hormone (LH) release was highly stimulated by all GnRHa treatments, with elevated plasma levels lasting for 2 days in injected fish (IN) and 2, 4 and 6 weeks in controlled‐release‐treated fish (EVAc, MC and EVSL, respectively), correlating with a 1, 3, 5 and 5 week period of stimulation of milt production, respectively. Plasma levels of the androgens testosterone (T) and 11‐ketotestosterone (11‐KT), were not significantly affected by the GnRHa treatments. Plasma T was high at early spermiation and declined sharply near the end of this period. Plasma 11‐KT levels declined continuously throughout the experiment. Levels of 17,20 β ‐dihydroxy‐4‐pregnen‐3‐one (17,20 β ‐P), a proposed maturation‐inducing steroid (MIS) in European sea bass, fluctuated around 0.2–1 ng ml −1 and were not greatly affected by the treatments. These results indicated a close correlation between sustained stimulation of LH release, achieved by GnRHa‐delivery systems, and long‐term enhancement of milt production. They also show an absence of changes in the common sex steroids, associated with elevated LH and enhanced spermiation.