Effects of salinity, type of feed, and shelter on development, growth and survival rate for larviculture of bule swimming crab (Portunus pelagicus Linnaeus
Abstract:
Crab (Potunus pelagicus) larval stages (zoea, megalopa, and crab) were commercially cultured in 1.3 m x 3.35 m x 0.70 m concrete tank under factorial design at densities of 225 zoea/L, 20 megalop/L and 2 crab/inch, respectively. The three levels of salinity of 24 ppt, 17 ppt and 30 ppt were the main factors for larviculture. Type of feed was the co-factor for zoeal culture while shelter was co-factor for megalopa and crab bulture. Survival rate, growth and metamorphosis period were examined.The result of the study indicated that the survival rate was significantly affected by type of feed (p<.05). The highest survival (56.1+-1.8%) was found in zoea fed on rotifer (Brachionus plicatitis) + newly-hatched Artemia. This value was significantly higher than that of zoea fed on rotifer and artemia flake group (p<.05) but it was not significant different from zoea fed on rotifer + water flea (Moina macroopa). Growth was significantly effected (p<.05) by salinity, type of feed and co-factor of salinity and feed. The length gain of zoea in 24 ppt and 27 ppt showed significantly (p<.05) higher than that of 30 ppt. The significant growth in length gain was found in zoea fed on rotifer + artemia nauplii. Furthermore, interaction between salinity and feed was also significantly (p<.05) affected on growth. The results revealed that zoea fed on rotifer + artemia nauplii under 24 ppt, 27 ppt and 30 ppt and rotifer + water flea under 27 ppt were significant highest (p<.05) but it was not significant different among these groups (p<.05). The significant lowest in length gain was found in zoea fed with rotifer + artemia flake and its growth would be significantly decreased (p<.05) when the salinity increased. Metamorphosis period (from hatch to the initial period of metamorphosed megalopa) significantly decreased when salinity increased. The significant (p<.05) shortest period (8.1+-0.4) from zoea megalopa stages was found in zoea under 30 ppt. The significant (p>.05) longest period was found in zoea fed on rotifer + artermia flake. However, the metamorphosis period was not significantly influenced by the interaction of salinity and feed.For megalopa and crab culture, survival rate, growth and metamorphosis period were not significantly affected by salinity as well as salinity and shelter. Survival rate of megalopa (58.9+-1.9%) using vertical line of oyster shell was significantly higher than that of using horizontal one and vice versa for crab stage (p<.05). On the contrary, growth of megalopa using vertical shelter showed significantly lower than that of using horizontal one and vice versa for crab stage (p<.05).