The floating goby Gymnogobius petschiliensis Rendahl is an amphidromous fish, which migrates upstream from the sea in the juvenile period and then inhabits not only freshwater areas but also brackish water. Most of the species that have such migratory polymorphism switch their osmoregulatory mechanism in synchrony with the timing of migration, but in G. petschiliensis it is known that even individuals living in freshwater areas behaviourally prefer brackish water to freshwater conditions in a laboratory. To clarify whether this species lives in freshwater areas with high osmoregulatory cost, the relationship between physiological cost and salinity was investigated using adult fish of the species captured in a freshwater area. Adults were kept individually in 13 L tanks with various salinity levels under fasted conditions. Their loss of body weight in freshwater conditions was more rapid than in 2/3 seawater, whereas the frequencies of horizontal and vertical movement in 13 L tanks did not differ significantly between freshwater and 2/3 seawater conditions. This suggests that the weight loss reflects not behavioural performance but physiological cost. In addition, no adults died even when transferred from freshwater to seawater conditions, indicating that they have high tolerance to salinity change in estuarine areas even after migrating to freshwater areas. These results support the hypothesis that G. petschiliensis migrates to freshwater areas while maintaining high hypo-osmoregulatory ability and paying a high physiological cost. Because G. petschiliensis phylogenetically originates from the coastal species, this example of migration without completely switching the osmoregulatory mechanism may help us to understand the diverse processes of upstream migration in marine fish.
|ジャーナル||Journal of Experimental Marine Biology and Ecology|
|出版ステータス||出版済み - 5 1 2019|
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