Narrowed temperature adaptability in non-natal osmotic environments of two euryhaline wanderers, dace and black porgy: implications for seasonal habitat changes

Many euryhaline wanderer species exhibit seasonal habitat changes, and temperature is suggested to play a key role in this phenomenon. To examine this possibility, we tested the hypothesis that adaptable temperature ranges of euryhaline wanderers are narrower in a non-natal osmotic environment than in their natal osmotic environment using dace Tribolodon hakonensis , a freshwater born euryhaline fish, and black porgy Acanthopagrus schlegelii , a marine born euryhaline fish. In both species, all individuals survived for 48 h in all the tested temperatures in their natal osmotic environments. In non-natal osmotic environments, however, both low (dace: 6 °C, black porgy: 10 °C) and high temperatures (dace: 30 °C, black porgy: 33 °C) significantly reduced their survival. These results indicate that euryhaline wanderers have a narrowed adaptable temperature range in non-natal osmotic environments. The similar trend observed in these two species of freshwater and marine fishes suggests that this may be a general characteristic in euryhaline wanderers and could be one of the causes of their seasonal movements.