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Keywords:

  • Labeo rohita;
  • grow-out;
  • monoculture;
  • nitrogen fertilization

Abstract

A grow-out monoculture experiment for rohu, Labeo rohita was conducted for 1 year in nine earthen ponds of 0.04 ha each to study the impact of varied frequency of nitrogen fertilization on fish growth. Ponds were stocked at 8000 fingerlings ha−1 density.  While ponds were applied with cattle manure and phosphate fertilizer at conventional dosages followed for grow-out carp culture, nitrogen fertilization was carried out at 15-, 10- and 7-day intervals and were designated as treatments T-1, T-2 and T-3 respectively. Although all the water parameters in the treatments were within the suitable range for grow-out carp farming, annual average concentration of dissolved oxygen (DO), plankton as well as availability of nutrients such as total ammonia- and nitrate-nitrogen in ponds were significantly higher in T-3 compared with T-1 and T-2. Greater fluctuation of critical parameters like DO, plankton concentration and total ammonia nitrogen were observed in T-1 and T-3 while the same were more consistent in T-2, revealing the prevalence of a better growing environment in the latter. Fish in T-2 also showed better specific growth rate, higher body weight attainment and higher biomass yield compared with the other two treatments, revealing the desirability of nitrogen fertilization at 10-day intervals in carp culture.