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Effect of Channel Catfish Stocking Rate on Yield and Water Quality in an Intensive, Mixed Suspended-Growth Production System

Green, Bartholomew W.
North American journal of aquaculture 2010 v.72 no.2 pp. 97
fish culture, Ictalurus punctatus, catfish, stocking rate, fish production, water quality, feed conversion, mortality, nitrogen content, pH
This study was conducted to determine the effect of stocking rate on yield of channel catfish Ictalurus punctatus and water quality in a mixed suspended-growth (biofloc) production system with zero water exchange. Channel catfish (National Warmwater Aquaculture Center 103 strain; average fish weight = 13 g) were stocked into nine 35-m2 tanks (28 m3/tank) at a rate of 2.9, 5.7, or 8.5 fish/m2 for a 238-d grow-out period. One 1.865-kW blower for every three tanks supplied air continuously through a diffuser grid (constructed of 2.5-cm-diameter polyvinyl chloride pipe) on the bottom of each tank. Well water was added only periodically to replace evaporative losses. Fish in each tank were fed daily as much floating catfish feed (32% protein, extruded pellets) as they could consume in a 20-min period. Channel catfish net yield ranged from 0.99 to 3.71 kg/m3 and increased linearly with stocking rate (r2 = 0.87). At harvest, mean individual weight (0.54 kg/fish), survival (62.1%), specific growth rate (1.54% per day), and net feed conversion ratio (1.9) did not differ significantly among stocking rates. Cumulative feed addition averaged 6.66 kg/m3 for the 8.5-fish/m2 treatment, significantly greater than the 4.04 and 2.96 kg/m3 for the 5.7- and 2.9-fish/m2 treatments, respectively, which did not differ. Mean nitrate-nitrogen concentration was significantly higher and mean pH was significantly lower in the 8.5-fish/m2 treatment compared with the other two treatments. There were no other differences in water quality among treatments. Total ammonia-nitrogen concentration was low throughout the experiment because of nitrification and phytoplankton uptake. This study demonstrated that high yields of channel catfish could be obtained by stocking up to 8.5 fish/m2 in a mixed suspended-growth production system.