Description of larval development stages of mud crab (Scylla Tranquebarica) and the effectiveness of antimicrobial agents against bacterial isolates.

This study described the larval development of mud crab, Scylla tranquebarica under hatchery conditions from first zoea to first crab stage. The crabs were fed daily with mussel (Meretrix meretrix) at 20 % of body weight and water quality was maintained by flow-through system of seawater. Newly hatched zoea were stocked at density of 50 ind/ml and fed with rotifer, Brachionus sp. (50 ind/ml), copepod, Acantia sp. (60 ind/ml) and brine shrimp, Artemia sp. nauplii (1 to 5 ind/ml) as the larvae developed to megalopa. Green water, Chlorella sp. was maintained in the rearing tank (100, 000 cells/ml) as food for the rotifers. The rearing water was siphoned prior to feeding at daily rate of 30 to 50 % starting on third day and increasing to 80 % as larvae grow bigger. The larvae were reared at temperature of 28.7 ± 0.2oC, salinity of 33.1 ± 0.4 ppt, dissolve oxygen above 6.7 ± 0.5 ppm and pH of 8.4 ± 0.1. The results showed that the fecundity estimated range from 1.46 to 4.68 million eggs per female per batch. The colour of the egg was initially yellowish and it gradually changed orange, brown, grey and dark grey before hatching. The diameter of the freshly laid egg was 308.29 ± 0.80 μm and 381.57 ± 8.46 μm just prior to hatch. Hatching rate was 17.47 to 47.26 %. The duration mean of each zoea stage was 3.6 ± 0.9 d and 3.4 ± 0.5 d for first and second zoea, respectively, while both third and fourth zoea was 3.2 ± 0.4 d and 2.4 ± 0.5 d for fifth zoea. However, megalopa took 7.0 ± 0.7 d while crab instar took 3.4 ± 0.5 d, and reached the first crab stage in 27 to 28 d from hatching. A total of 32 bacteria isolate have been successfully isolated from carapace part of adult and larval stage namely Aeromonas spp. (n = 7), Edwardsiella tarda (n = 5), Klebsiella spp. (n = 7), Salmonella spp. (n = 7), Vibrio alginolyticus (n = 4) and Vibrio parahaemolyticus (n = 2). Antibiogram of bacteria isolate were tested with 16 types of antibiotics using disk diffusion method. Nalidixic acid, flumequine and oxytetracycline found to be effective in inhibiting the growth of bacteria isolate with all were sensitive to these antibiotics. Approximately 67.5 to 88.3 % bacteria were resistance with heavy metal tested using agar dilution method. Antimicrobial property of 30 local plants of methanolic extract using hole plate diffusion method revealed that Artabotrys uncinatus (Lam.) has strong antimicrobial effect against the all the bacteria. Therefore, this study provided information on larval development and bacteria associated with mud crab and it is important to develop hatchery seed production technology to reduce the mortality during larval culture.