EFFECTS OF ADDED SUBSTRATE ON THE PRODUCTION AND POPULATION CHARACTERISTICS OF FRESH-WATER PRAWNS MACROBRACHIUM-ROSENBERGII IN PONDS

The effects of added substrate on the growth and population characteri stics of freshwater prawns raised in ponds were evaluated. Juvenile pr awns (0.3 +/- 0.2 g) were stocked into six 0.04-ha ponds at a density of 59,280/ha. In three randomly selected ponds artificial substrate wa s added sufficient to increase available surface area approximately 20 %. Three control ponds received no added substrate. Added substrate co nsisted of PVC frames with horizontal plastic mesh and vertical suspen ded seines. Prawns were fed a commercial diet (32% protein) twice dail y according to a computer-generated feeding schedule. At harvest avera ge individual weight, daily yield, and total yield were significantly higher (P < 0.05) in ponds with added substrate (37 g, 12.0 kg/ha per day, and 1,268 kg/ha, respectively). There was no significant differen ce in survival between treatments, averaging 59% overall. In ponds wit hout substrate the number of small males (SM) was significantly higher and the number of orange claw males (OC) was significantly lower than in ponds with added substrate. Average individual weights of blue cla w males, orange claw males, reproductive females, and virgin females w ere significantly higher (P less than or equal to 0.05) in ponds with added substrate. Prawns raised in ponds containing added substrate had growth rates and population structures characteristic of prawns stock ed at lower densities. Optimum relationships between stocking rates an d amounts and types of added substrate should be evaluated as possible methods to increase production levels.