Influence of water exchange rates on fingerling production in Indian major carps in large outdoor concrete tanks

Abstract

Influence of varied water exchange (total of 0%, 40%, 60%, 80% and 100% in four phases during three months) on fingerling production of Indian major carps-catla, rohu and mrigal under polyculture was evaluated in large outdoor concrete tanks (50 m2). Rearing density of 30 fry m−3 was used. Survival in the control tanks reduced during the 2nd month unlike the treatments, attributed to lack of water exchange in the tanks. While no marked variation in water quality was observed among the control and treatments, graded water exchange led to proportionate improvement in the fingerling performance in terms of survival and growth in the treatments. Harvested total lengths of fingerlings were similar in all, irrespective of varied exchange levels. Although no significant variation in net weight gain (NWG) and specific growth rate (SGR) were observed among the treatments during 1st and 2nd months of rearing in any of the species, these attributes increased significantly during 3rd month with higher water exchange in treatments. The harvested body weight (HBW) also increased significantly with increased exchange level. However, survival, HBW, NWG and SGR remained similar in all species between the 80% and 100% water exchange levels. Treatment with 80% water exchange had higher water productivity in terms of number and biomass production of fingerlings per unit (m−3) of TWU and CWU for which, the study recommended 80% to be the ideal total water exchange required for fingerling production of IMC in concrete tanks.