Effects of carbohydrate source for maintaining a high C:N ratio and fish driven re-suspension on pond ecology and production in periphyton-based freshwater prawn culture systems

The present research investigated the effect of carbohydrate (CH) source for maintaining a high C:N ratio, and tilapia driven bioturbation on pond ecology, production and economical performances in C/N controlled periphyton-based (C/N-CP) freshwater prawn ponds. Two carbohydrate sources (high-cost tapioca starch and low-cost maize flour) were compared in 40 m2 ponds stocked with 80 freshwater prawn (Macrobrachium rosenbergii) juveniles (individual weight 0.81 ± 0.03 g) and 20 finfish fingerlings (Nile tilapia, Oreochromis niloticus and Indian major carp rohu, Labeo rohita) in three different combinations: 100% tilapia, 50% tilapia + 50% rohu, and 100% rohu (individual weight 27.7 ± 0.6 g). The CH sources for increasing C:N ratio from 10 (as in feed) to 20 had no significant effect (P>0.05) on water quality parameters, abundance of natural food (plankton, periphyton and benthos) and production of prawn and finfish. However, different fish combination had significant effects on pond ecology. The highest P04-P (P0.05) by the different stocking combinations of finfish. The net yield and survival of finfish were significantly higher in 100% tilapia ponds and lower in 100% rohu ponds resulting in 58% higher combined net yield (both prawn and finfish) in the former treatment during a 120-d culture period. This treatment gave the best economic return in terms of benefit-cost ratio while maize flour was used as CH source. In conclusion, maize flour can be used as an alternative cheap on-farm CH source for maintaining a high C:N ratio and tilapia driven re-suspension in C/N-CP system improves culture environment, natural food utilization, production and economic return, further enhancing economic sustainability of C/N-CP freshwater prawn farming system