Effect of water temperature on the survival rate of swimming crab, Portunus trituberculatus, larvae reared at pH 9.25

摘要

In order to prevent fungal infection caused by Halocrusticida okinawaensis in swimming crab, Portunus trituberculatus, larvae are reared at pH 9.25 in hatcheries based on our previous report. In the present study effect of water temperature on the survival rate of swimming crab larvae reared at pH 9.25 was investigated. Acute toxicities of pH 9.25 to swimming crab zoea-I were not observed at ammonia-N concentrations lower than 1 mu g/ml at 20-30 deg C, but a lower survival rate of larvae was observed at 3(TC when ammonia-N concentration was 8 mu g/ml. In the experiment on long-term effect of pH 9.25 where larvae from zoea-I through zoea-IV were reared for 12-14 days at around 20 deg C or for 7-8 days at 25, 27 and 30 deg C, survival rates of swimming crab larvae reared at pH 9.2 were reduced at temperatures higher than 27 deg C. These results indicate that the pH 9.25 rearing method as a prophylactic measure against fungal infection can be applied when water temperature is lower than 27 deg C.