Water quality management in earthen ponds using an optimum carbon/ nitrogen ratio

The main goal of the current study was to evaluate the effects of C/N ratio on water quality parameters and production level at high stocking density pond. The C/N ratio of the experimental ponds were arranged by addition of corn starch to the pond. There were three treatments in the current study; control one without corn starch addition and treatments two and three which contain C/N rations of 15 and 20. We had three replicates for each treatment and the experimental unit was nine uniform 400 m2 earthen ponds. Two hundred and forty juvenile common carp, 120 silver carp and 40 bighead with  initial weights of   60.74± 0.40, 50.2±0.39, 51.02±1.11 were introduced to each of experimental unite. The results showed that increasing C/N ratio to 15 and 20 improved growth performance and nutrient efficiency in common carp (P<0.05). Similar to common carp, bighead growth and feed efficiency improved by feeding on high C/N ratio diets compared to low one  (P<0.05). However, silver carp growth and feed efficiency reduced by addition of carbon source to the water (P<0.05). Different C/N ratio did not change survival rate of fish during the experiment. Ammonium nitrogen, nitrite and phosphate were measured lower at 20and 15 C/N ratio than those of control one (P<0.05). However, nitrate concentration was not influenced by the C/N ratio. The current study revealed that the application C/N ratio can introduce an alternative for an improve in growth performance and water quality control. In addition, water consumption and waste generated within the pond  can be managed by application of a proper  C/N ratio.