Spermatozoa of Sharpsnout sea bream ( Diplodus puntazzo) and European sea bass ( Dicentrarchus labrax) express opioid receptors

Abstract

Endogenous opioid peptides (EOP) are molecules affecting many biological functions influencing productive and reproductive performance. They increase in stress conditions and interact with specific opioidergic receptors (OR): delta, kappa and mu. Several studies in other animal species suggest that they can also affect sperm cell motility. In fish the ionic external environment modulates the increase of intracellular calcium ion that is required to activate sperm motility after spawning. In mammals OR are functionally associated to calcium channels and in fishes calcium is highly required for fish sperm activation. In this study the presence of OR on spermatozoa of two Perciform fish, the sharpsnout seabream ( Diplodus puntazzo, family Sparidae) and the European sea bass ( Dicentrarchus labrax, family Moronidae) was investigated; the two species were chosen for their importance in Mediterranean aquaculture. The analysis by indirect immunofluorescence evidenced the presence of OR on sperm cells of these fishes. Delta, kappa and mu opioid receptors appeared differently localized on the surface of the sperm cells of sharpsnout seabream and European sea bass. Opioidergic receptors on fish spermatozoa could be a new target for reducing stress associated to captivity reproduction in fish farms by EOP antagonists.