Effect of Salinity on Mating, Hatching and Survival Rate of the Zoea Larvae of Sundaic Paddler Crab (Varuna yui Hwang & Takeda, 1984)

Abstract

Sundaic paddler crab (Varuna yui) is one of economic grapsid crabs in Thailand. Over the past ten years, the crab population has decreased dramatically, because they are caught for consuming during their breeding season. Increasing the Sundaic paddler crab numbers from the hatchery is necessary. The aim of this study was to determine the optimal water conditions for increasing the population of Sundaic paddler crab from hatcheries. An investigation was conducted to determine salinity effects on the mating and hatching rate and survival of zoea 1 stage. The results showed that seven salinity levels (0, 5, 10, 15, 20, 25 and 30 ppt) had a significant (p<0.05) effect on mating success, hatching and zoea survival of Sundaic paddler crab. Mating and hatching were not found in salinity 0 to 15 ppt. The mating success was 100 percentages for salinity of 20 and 25 ppt. Number of zoea 1, hatched at salinity of 20 and 25 ppt were not significant different (p>0.05). When hatched zoea 1 stage were stocked in seven salinity levels, it was found that they could not survive in salinity of 0 to 5 ppt and the survival of zoea 1 in salinity 20 were significant highest (p<0.05). This study suggests the optimal salinity level for breeding V. yui, to release into the nature is 20 to 25 ppt.