Male silver eels mature by swimming

Abstract

Background. If European silver eels are prevented from reproductive migration, they remain in a prepubertal stage by dopaminergic inhibition of pituitary activity. Because this inhibition is likely a requirement for an extended female growth stage, we tested if it is sex-specific by subjecting both sexes to stimulation by GnRHa (Gonadotropin-Releasing Hormone agonist) - injection or 3-months swimming in seawater. Results. In contrast to females, males showed a two- to three-fold higher LHβ (luteinising hormone β subunit) - expression, a three- to five-fold higher GSI (Gonadosomatic index) and induced spermatogenesis when compared with the untreated control group. Conclusion. Dopaminergic inhibition is thus not effective in males and swimming results in natural maturation, probably via GnRH-release. © 2008 Palstra et al; licensee BioMed Central Ltd.