INFLUENCE OF COOLING OF MUD CRAB JUVENILES IN ICE BATH ON SURVIVAL AND PHYSIOLOGICAL CHANGES DURING STORAGE  

Considering that mud crab aquaculture is primarily dependent on the limited supply of wild seeds, mortalities associated with capture, handling and storage is serious concern for the industry. In lieu of the practice of cooling crabs in a chamber, crabs (S. olivacea, 27-44g) were directly immersed in seawater of different temperatures (4^oC, 7^oC, 15^oC and 29^oC/ambient) prior to tying and storage. Crabs that were immersed at 15^oC for 3 min obtained ~90% survival which was significantly higher than the rest of the treatments after 48h and 72h of storage (P<0.05) (Fig.1).

Based on vigour index, crabs cooled at 15^oC obtained the highest percentage of crabs that were classified as lively (~53%) after 48 h and 72 h storage (Table 1). Among the crabs that survived the 48 and 72 h storage, those cooled at 15^oC also obtained the highest survival in the recovery tanks after 12 and 24 h.  

The survival and vitality results may be explained by the lower glucose and lactic acid levels detected in the haemolymph of crabs that were cooled at 15^oC and 7^oC (<1 mmol L^-1) compared to 29^oC/ ambient and 4^oC (Table 2).  Glucose and lactic acid levels below 1 mmol L^-1 were reported to indicate that the crabs were not stressed.

This study therefore showed that cooling of crabs by immersion can be a technique for improving survival of harvested crabs.