Submitted to: North American Journal of Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/24/2009
Publication Date: 4/1/2010
Citation: Green, B.W. 2010. Effect of channel catfish stocking rate on yield and water quality in an intensive, mixed suspended-growth production system. North American Journal of Aquaculture. 72:97-106.
Interpretive Summary: Fish in aquaculture production units are fed a formulated ration to ensure they grow quickly. Ammonia is the primary metabolic by-product of feed protein digestion and is excreted by fish into the pond water. Feeding rates increase as the intensity of production increases, which leads to increased excretion of ammonia by the fish. High concentrations of the un-ionized form of ammonia are toxic to fish. Thus, it is important to develop methods to manage accumulation of ammonia in the pond water as fish production systems are made more intensive. In catfish ponds, algae populations utilize ammonia as a source of nitrogen for growth, and so are primarily responsible for controlling ammonia concentration. Bacteria suspended in the water column also can play a role in controlling ammonia concentration. The assemblage of algae, bacteria, and particulate organic matter suspended in the water column is referred to as a mixed suspended-growth system. This experiment was conducted to determine whether the channel catfish could be grown successfully at high numbers in 377 square foot tanks using the mixed suspended-growth system. Tanks were stocked with 1.5 to 4 times as many channel catfish as are stocked typically in production ponds. Catfish were fed fish feed daily at rates that were 2.5 to 5 times greater than used in conventional commercial ponds. Ammonia concentration in the water remained low throughout the experiment because it was utilized by the algal and bacterial populations present in the water column. The net production of channel catfish in this experiment was 0.5 to 5.3 times greater than the quantity of fish typically harvested from production ponds. This experiment demonstrated that channel catfish could be grown successfully in a mixed suspended growth system where fish were stocked at high numbers and fed at a high rate. The results of this research serve as the basis for additional research to optimize parameters for this more intensive production system.
Technical Abstract: This study was conducted to determine the effect of channel catfish (Ictalurus punctatus) stocking rate on yield and water quality in a mixed suspended-growth production system (bio-floc) with zero water exchange. Channel catfish (National Warmwater Aquaculture Center 103 strain; average weight = 13 g/fish) 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/3 tanks supplied air continuously through a 2.5-cm diameter polyvinyl chloride pipe diffuser grid 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 32% protein floating extruded catfish feed as they could consume in a 20-min period. Channel catfish net yield ranged from 0.99-3.71 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%/d), 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 to 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 (bio-floc) production system.