Adults of the marine-originated amphidromous goby (Gymnogobius petschiliensis) inhabit both freshwater and brackish-water areas, unlike many other amphidromous species, which spend their entire lives, except the larval stage, in freshwater. Furthermore, adult G. petschiliensis individuals incur higher osmoregulatory costs in freshwater than those in hypertonic brackish water under laboratory conditions, suggesting that the ecology of the species is largely dependent on high-salinity (ancestral) environments. Therefore, a detailed information on the ecology of G. petschiliensis will help elucidate the diversity and evolution of amphidromy. Here, this study assessed the habitat use and freshwater dependency of G. petschiliensis in two streams in central Japan. Year-round surveys showed that adult density was higher in freshwater than in brackish water during the non-spawning season. This implies that adults chose salinity habitats according to ecological conditions (e.g. inter- and intraspecific competition, and predation risk) without being bound by physiological preferences. Conversely, most egg clutches were found in brackish water. Furthermore, adult density in brackish water increased with the increase in spawning events, suggesting that the adults migrated downstream for spawning. This preference for spawning in brackish water rather than in freshwater may be attributed to the constraints of their reproductive physiology.

海洋起源的两栖虾虎鱼 ( Gymnogobius petschiliensis ) 的成鱼生活在淡水和咸水区，这与许多其他两栖虾虎鱼不同，它们的一生（幼虫阶段除外）都在淡水中度过。此外，在实验室条件下，成年G. petschiliensis个体在淡水中比在高渗微咸水中产生更高的渗透调节成本，这表明该物种的生态在很大程度上依赖于高盐度（祖先）环境。因此，有关G. petschiliensis生态学的详细信息将有助于阐明两栖动物的多样性和进化。在这里，本研究评估了G. petschiliensis的栖息地利用和淡水依赖性在日本中部的两条河流中。全年调查表明，在非产卵季节，淡水中的成虫密度高于咸水中。这意味着成年人根据生态条件（例如种间和种内竞争以及捕食风险）选择盐度栖息地，而不受生理偏好的约束。相反，大多数鸡蛋离合器是在微咸水中发现的。此外，咸水中的成虫密度随着产卵事件的增加而增加，表明成虫向下游迁移产卵。这种在咸水中而不是淡水中产卵的偏好可能归因于它们生殖生理的限制。