Effects on Growth and Water Quality of Feeding Exogenous Plankton Compared to Use of Manure in the Culture of Mrigal,Cirrhinus mrigala, and Rohu,Labeo rohita, Fry in Tanks

Advanced fry (2.0-3.5 g) of mrigal, Cirrhinus mrigala, and rohu, Labeo rohifa were cultured in 9,580-L tanks for 90 days. Individual weight gain and total yield were compared among five culture regimes: (1) live zooplankton fed to fry stocked at 1,312 fry/tank (LF); (2) fry stocked at 1,642 fry/tank (HLF); (3) manurebased system (l,312 fry/tank) without water exchange (M); (4) manured- based system (1,312 fry/tank) with water exchange (EM); (5) a control (1,312 fry/tank) (C) fed with mustard oil cake and boiled rice treatment. There were three replicates for each treatment. Weight gain of both species of carp stocked at the LF rate and fed zooplankton was significantly higher (P < 0.05) than that of fish in the other treatments. Survival of rohu and mrigal was significantly higher (P < 0.05) in LF treatment than that in M treatment. Yields for both species in the HLF were significantly higher (P < 0.05) than those in the remaining treatments. Dissolved oxygen was lower in M (P < 0.05) than that in other treatments. Mean BOD, COD, phosphate, nitrate-N were markedly higher (P < 0.05) in the M treatment compared to measurements in other systems. The results suggest that raising carp fry in nursery ponds using exogenous feeding of zooplankton is of considerable importance because such feeding would support high rates of survival and growth through maintenance of better water quality and greater abundance of zooplankton in the culture system.