Estuaries and coastal lagoons play a key role in the functioning of coastal ecosystems and represent important natural areas for fish communities. Species living in these habitats often show specialised ecological and life history traits. The reproductive periodicity of a northern population of the Mediterranean killifish Aphanius fasciatus was assessed using the male courtship behaviour as indicator of reproductive motivation under laboratory conditions. Timing of egg development was also checked to further support the existence of a tidal-related periodicity. Using a statistical model applied to the intensity of courtship behaviour measured over a two-month period, a semilunar periodicity was revealed, with two main peaks corresponding with full moons. Both behaviours and timing of egg development were consistent with a periodicity of 14 days, suggesting that the tidal cycle drives the reproduction of A. fasciatus in Northern Adriatic saltmarshes. The findings are assessed with a comparative approach within both European and North American transitional waters.