Comparison of locally available diets on S. paramamosain crablet survival and growth

Previous experiments have found that highest survival and growth was obtained with a diet of peeled shrimp, however, this is expensive. During the dry season Artemia biomass is a cheap and readily available alternative.

Net cages were stocked with 15 stage 1 crabs/m² and provide with shelters and fed with either live or frozen Artemia biomass or peeled shrimp. Initially growth and survival were significantly higher in the treatments fed Artemia. However, after one month there was no difference in final weights (~1.5g) or carapace widths (~1.8cm) between treatments. However survival rates of 53% were significantly lower than those fed Artemia. 

The use of either frozen or live Artemia biomass may help reduce cost, increase survival and subsequently increase economic effectiveness in crab production.


Comparison of lined nursery pond and nets cage rearing systems on the performance of juvenile S. paramamosain

In order to compare the efficiency of different rearing systems to produce crabs on growing (>1.5cm CW), net cages (4×5×1.8 m) were stocked with 10, 15 & 30 crab 1/m² while ponds lined with plastic (6×5×0.8) were stocked with 66 crab 1/m². Both were provide with shelters in the form of bundles of twigs and suspended net bags of oyster shells. 

Depressed survival and growth due to higher (33ppt) than optimal salinity (15-20ppt), was observed after 40 days. There were no significant differences in survival between treatments; however the weight of crabs grown in ponds was significantly heavier.

Fitness of hatchery-raised (HR) and wild S. paramamosain

Prior experiments had suggested that HR juveniles from central Vietnam could not compete with wild crabs when co-stocked, therefore improved HR juveniles raised in ponds as supposed to individually. Crabs raised individually have no experience of predator evasion or experienced cannibalistic pressure on the weakest animals. 

Nine ponds were stocked with individually micro-wire tagged crabs (50:50 wild:HR crabs, HR crabs and wild crabs). After 3.5 months HR crabs displayed significantly higher growth rate for both carapace width (F=51.9, p<0.0001) and weight (F=42.8, p<0.0001) than that of wild crabs in separate ponds. However in mixed ponds while final carapace width was significantly larger in HR crabs, there was no difference in weight and survival was greater amongst wild crabs. In separate ponds, there was no difference in survival between HR and wild crabs. 

Larval rearing tanks at Cantho University

Mud crab broodstock facility at Cantho University

Trial ponds at the research station in Vinh Chau

References

Keenan, C. P., Davie, P. J. F. and Mann, D. L. (1998). A revision of the genus Scylla de Haan, 1833 (Crustacea : Decapoda : Brachyura : Portunidae). Raffles Bulletin of Zoology 46, 217-245.

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