Journal
<p>To understand the ecology and environmental tolerances of newly hatched larvae of the amphidromous fish</p>
<p>Sicyopterus japonicus during their downstream migration, the salinity tolerance of eggs, 0–15 day old larvae,</p>
<p>and adults, and the temperature tolerance, specific gravity and phototaxis of hatched larvae were examined.</p>
<p>Tolerances of adults were measured as survival after a 24 h challenge in freshwater (FW), brackish water (1/</p>
<p>3 SW) and seawater (SW). The survival rate of adult S. japonicus was 100% in FW and 1/3 SW, while none</p>
<p>survived in SW. Hatching success of eggs (30 eggs each) was significantly higher in FW (mean: 73%) and 1/3</p>
<p>SW (73%) than in SW (19%). Tolerance of newly hatched larvae to salinity and temperature was investigated</p>
<p>in different combinations of salinities (FW, 1/3 SW and SW) and temperatures (18, 23 and 28 °C). Larval</p>
<p>survival was significantly different in each salinity and temperature. Survival rate was significantly higher in</p>
<p>1/3 SW than in FW and higher in SW than in FW at 23 °C and 28 °C. At the latter part of the experiment, there</p>
<p>was no survival in FW and at 28 °C. Survival was higher in lower temperatures, but larval development did</p>
<p>not occur in FW. Specific gravity of newly hatched larvae was 1.036 at 28 °C and 1.034 at 23 °C. When</p>
<p>exposed to a light source on one side of an aquarium, larval distribution was not affected. Our results</p>
<p>indicated larval S. japonicus are more adapted to brackish water and seawater than freshwater, while the</p>
<p>adults and eggs are more adapted to freshwater and brackish water than seawater. This is consistent with</p>
<p>their amphidromous life history with growth and spawning occurring in freshwater and the larval stage</p>
<p>utilizing marine habitats.</p>
