Abstract
Gradual transfer experiments were conducted to see whether Japanese dace Tribolodon hakonensis (freshwater species) and Japanese black porgy Acanthopagrus schlegelii (marine species) could acclimate to high and low temperatures in natal and non-natal osmotic environments. Two groups of each species, one acclimated to their natal osmotic environment and the other to a non-natal osmotic environment, were exposed to gradual temperature changes. Under high temperature conditions, the plasma osmolality (Posm) of both species approached the osmolality of ambient water, and high mortality was observed in the non-natal osmotic environments but not in the natal osmotic environments. In contrast, there was no clear evidence that the osmoregulatory capacity of either species had declined under low temperature conditions in the natal and non-natal osmotic environments. Limited adaptation of these fishes to non-natal osmotic environments at high temperature suggests that global warming may impair their entry to non-natal habitats.
Highlights
Euryhaline wanderer fishes in the temperate zone are known to exhibit seasonal habitat changes (Day et al 1989; Able and Fahay 1998; Ishitobi et al 2000; Able and Fahay 2010)
In SW, which is a non-natal osmotic environment for this species, the Posm showed a significant increase in association with the increase in ambient water temperature, and the estimated plasma osmolality at 31 °C was 13% higher than that at 20 °C (Fig. 1b)
These results clearly show that the Posm of both species approached the osmolality of ambient water under high temperature conditions in the non-natal osmotic environments
Summary
Euryhaline wanderer fishes in the temperate zone are known to exhibit seasonal habitat changes (Day et al 1989; Able and Fahay 1998; Ishitobi et al 2000; Able and Fahay 2010) These species typically enter nonnatal osmotic environments (hypertonic environments for freshwater species and hypotonic environments for marine species) in estuaries during spring to summer and migrate back to their natal osmotic environments during fall and winter (Nakamura et al 2016). Since these species typically enter estuaries in warm seasons, coastal warming, which is occurring across broad areas of the world’s coastlines (Lima and Wethey 2012), may force them to tolerate higher temperatures in non-natal osmotic environments This may be problematic because the osmoregulatory capacities of euryhaline fishes can be affected by water temperature (Sardella et al.2008; Nakamura et al 2016; Masroor et al 2018; Vargas-Chacoff et al 2018). In order to estimate the potential effect of global warming on the migratory ecology of euryhaline wanderers, the capacity to acclimate to high and low temperatures needs to be validated under gradual temperature changes
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