The present research investigated the effect of carbon/nitrogen ratio (C/N ratio) control in ponds with or without substrate addition for periphyton development on production of giant freshwater prawn. C/N ratios of 10, 15 and 20 were investigated in 40 m¿ 2 ponds stocked with 2 prawn juveniles (5.023 ± 0.02 g) m¿ 2 with or without added substrates for periphyton development. The various treatment combinations of C/N ratio and periphyton substrate addition are abbreviated as `CN10¿, `CN15¿, `CN20¿, `CN10 + P¿, `CN15 + P¿ and `CN20 + P¿, P representing periphyton substrate. A locally formulated and prepared feed containing 30% crude protein with C/N ratio10 was applied. Tapioca starch was used as carbohydrate source for manipulating C/N ratio and applied to the water column separately from the feed. Increasing the C/N ratio from 10 to 20 reduced (P <0.001) the total ammonia-nitrogen (TAN), nitrite¿nitrogen (NO2¿N) and nitrate¿nitrogen (NO3¿N) in water column and total Kjeldahl nitrogen (TKN) in sediment. The addition of substrates only influenced the NO2¿N concentration in the water column (P <0.001). Increasing the C/N ratio raised the total heterotrophic bacterial (THB) population in the water column, sediment and periphyton (P <0.001). It also increased the dry matter (DM), ash free dry matter (AFDM), and chlorophyll a content of periphyton (P <0.001). The lowest specific growth rate (SGR), the highest food conversion ratio (FCR), and the lowest protein efficiency ratio (PER) were recorded in treatment CN10 (P <0.05). The addition of substrates did not influence size at harvest (P > 0.05) but improved the survival from 62.8 to 72% (P <0.001). Increasing the C/N ratio from 10 to 20 increased the net yield by 40% and addition of substrate increased the net yield by 23%. The combination of C/N ratio control and substrate addition increased the net yield by 75% from 309 (CN10) to 540 (CN20 + P) kg ha¿ 1 (120 days)¿ 1. This 75% higher production concurred with (1) a lower inorganic nitrogen content in the water column, (2) a higher THB abundance supplying additional single cell protein to augment the prawn production, and (3) an improved periphyton productivity and quality.
- fish ponds