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A specific chronology for puberty and changes at the brain–pituitary–gonad axis for sea bass are reviewed. Recent findings demonstrate that the Kisspeptin system, gonadotropin releasing hormones, follicle stimulating hormone, 11-ketotestosterone, and leptin are potential candidates for the onset of puberty of this fish species, stressing the importance of the daily and annual rhythms of some of these hormones. Environmental control of puberty is also reviewed, specifically the manipulations of constant photoperiods for altering or even suppressing the onset of puberty in sea bass. Recently, a possible narrow sensitive period for suppressing gonadogenesis in sea bass has been identified. [ABSTRACT FROM AUTHOR]

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; 100 μg kg−1), slow release implants (EVSL; 100 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 17,20β-dihydroxy-4-pregnen-3-one (17,20β-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. [Copyright &y& Elsevier]