Histology and morphometrics of testes of the white-sided dolphin (Lagenorhynchus acutus) in bycatch samples from the northeastern Atlantic

The testes of 31 Atlantic white-sided dolphins, Lagenorhynchus acutus bycaught in the northeastern Atlantic were studied by histological and morphometric techniques. Twenty specimens were classified as mature, nine as immature and two as pubescent. Between immature and mature specimens there were overlappings in body length and body weight, but clear differences in the diameter of seminiferous tubules (<80 and >80 μm) and the proportion of seminiferous tubules to interstitial tissue (ST:INT-ratio). Also relative testes weight differed clearly. The pubescent specimens showed intermediate characteristics. Spermatogenetic activity of mature dolphins ranged from quiescent to different degrees of activity and varied even in animals from the same site and capture date. The fact that we found mature males with quiescent testes suggests a seasonal rather than a continuous spermatogenesis. We assume that sexual activity in L. acutus begins at an age of 7–8 GLGs and that the reproductive season of this species in the northeastern Atlantic starts in February. Further, the ultrastructure of the spermatozoon is similar to that of the related Lagenorhynchus obliquidens.