A study of substrate addition for Macrobrachium rosenbergii in intensive, closed systems

The freshwater prawn, Macrobrachium rosenbergii, is an important aquacultural species because of its large size and freshwater culture. Currently all ventures producing this prawn are using extensive, pond culture. The nursery stage 0.1-3.0 g, has successfully controlled in intensive, closed systems, and most producers use this method for gaining larger individuals to stock into their ponds. The grow-out phase, 3.0-30.0 g, has little research to show successful growth under intensive, closed conditions. This study describes the design of a culture system that provided up to 36 tanks with an equivalent environment for growth experimentation. This culture system was used to evaluate a substrate and stocking density experiment for the grow-out phase of the freshwater prawn. A central water recycling system was designed with a rotating biological contactor, for nitrogenous waste removal; an inclined plane filter, for major debris removal; an air stone system and mechanical vane aerator, for aeration of the feed water; and a small pump with a plenum chamber, to split the feed water flow to the tanks. The water returned to the recycling system by gravitational flow. The water quality was found to be acceptable for prawn growth at a loading factor of 810 g/m$\sp3$. Specifically, dissolved oxygen content stabilized to 4.0 mg/l, ammonia and nitrites were kept below 0.1 mg/l, nitrates averaged 5.9 mg/l, and BOD\u27s averaged 1.3 mg/l in the return water. The effect of substrate on survival and growth rates at three stocking densities was studied in comparison to controls without substrate. Two types of substrate, a tube and a level (tiered) structure, were introduced to the treatment tanks. Three densities of prawns, 10.8, 21.5, and 32.4 ind/m$\sp2$, were grown with three replications for each substrate/density combination. The prawn experiment was analyzed statistically using a survival and growth model. It was found that differences in survival between substrates were statistically insignificant. The substrates did improve growth by increasing total biomass in the treatment tanks with a final stocking recommendation of 158.5 ind/m$\sp3$ using a tube structure