The Effect of Water Depth on Efficiency of Freshwater Prawn (Macrobrachium rosenbergii, de Man) Culture in the Brackish Area

Investigating the effect of water depth on the efficiency of the giant freshwater prawn, Macbrobrachium rosenbergii, cultured in the rice field was conducted in a brackish water area with salinity level of 0 – 6g L^-1. The experiment was designed in triplicate with two water depths on the platform; depths varied between 0.3– 0.4 and 0.5– 0.6m for low and high water depths, respectively. Postlarvae (PL) 15 were stocked in the rice field at a density of 30,000 PL ha^-1 for 180 days. The results showed that water quality parameters in both water depths were in the suitable ranges for prawn growth. However, temperature, dissolved oxygen, N-NH₄⁺ and N-NO₂^- recorded better values in the high water depth compared to the low one. Furthermore, prawns cultured in low water depth had smaller final weight and lower survival and yield (39.6 g, 25.4%, and 292 kg/ha, respectively) than those cultured in high water depth (46.9 g, 30.5%, and 358 kg/ha). Significant differences (P <0.05) were detected between the two water depth treatments. A similar result was observed for net income, profit and cost-benefit ratio. These findings suggest that prawn culture in the rice fields in brackish water areas with high water depth (0.5– 0.6m) provided an optimal environment for prawns, improving the financial efficiency of the culture system. Whereas, low water depth (0.3– 0.4m) could be an alternative in times of water shortage in the prawn production cycle.