Density-dependent water use in carp polyculture: Impacts on production performance and water productivity

The total water use (TWU) and consumptive water use index (CWUI) in carp polyculture under varying intensity levels [T 1 : 6000 fingerlings ha − 1 , T 2 : 8000 fingerlings ha − 1 , T 3 : 10,000 fingerlings ha − 1 ] were quantified. Treatment-wise estimated TWU was 3.71 × 10 4 , 3.92 × 10 4 and 4.34 × 10 4 m 3 ha − 1 180 d − 1 while, the CWUI was 6.38, 5.61 and 5.89 m 3 kg − 1 fish production in T 1 , T 2 and T 3 , respectively. The estimated evaporation and seepage loss ranged between 2.1–3.1 and 1.9–2.8 m 3 water kg − 1 fish production respectively and contributed significantly to consumptive water use (CWU). Treatment-wise sediment load ranged between 57.1 and 61.1 m 3 t − 1 fish biomass. Faster growth rate and biomass contribution (%) to yield was maximum by C. catla followed by C. mrigala and L. rohita in all the treatments. In this study, under best management practice (T 2 ), 1 m 3 of water produced 178 g of carp biomass and its economic value per unit of water used (USD m − 3 ) greatly exceeds that of T 1 and T 3 . Among the treatments, minimization of total water use (3.92 × 10 4 m 3 ), CWU (2.03 × 10 4 m 3 ) and water exchange (0.20 × 10 4 m 3 ) at stocking density of 8000 fingerlings ha − 1 (T 2 ), resulted in higher ( P − 1 180 d − 1 ), output value - cost of cultivation ratio (1.88), net consumptive water productivity (USD 0.15 m − 3 ) and lower AFCR (1.74). Further, farming systems with low water exchange, serves to keep the water quality suitable for the fish growth, improves water use efficiency and helps in minimizing the quantity of pollutant outputs. Statement of relevance This paper presents findings and analysis, from a methodologically rigorous investigation and provides insight regarding density-dependent optimum water use, its effect on pond water quality, sedimentation rate, growth performance and water productivity. The knowledge derived from this study may be a basis to optimize pond rearing efforts in carp polyculture and the water management strategies can be tailored to prevent wasteful use of water and enhance water use efficiency and water productivity.