Abstract
The tolerance ofChrysichthys nigrodigitatus (19.0 ± 3.3 g) acclimated to various salinities and exposed to abrupt or gradual (stepwise) increase in salinity was determined at temperatures of 26.0–27.4 °C under laboratory conditions. No mortality occurred when fish were transferred from freshwater to 22 ppt while 30% mortality was recorded at 23 ppt. The median lethal time (LT50) decreased with increase in salinity from 2120 min at 24 ppt to 165 min at 40 ppt. The median lethal salinity (LS50) increased with increase in acclimation salinity. The LS50 forC. nigrodigitatus acclimated to freshwater, 13, 18 and 25 ppt was 24, 28, 30 and 35 ppt respectively. Likewise, the LS50 after gradual (stepwise) increase in salinity at the rate of 1 ppt per day was 44 ppt. Such findings confirm the euryhaline nature ofC. nigrodigitatus and indicate that the species can tolerate a wide range of salinities through gradual acclimation.
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