EFFECT OF EXTREME STOCKING DENSITIES ON HYBRID CATFISH PRODUCTION AND WATER QUALITY IN EARTHEN PONDS

Earthen ponds used for ictalurid aquaculture have traditionally been regarded as phytoplankton-based systems, with much of the nitrogenous waste being assimilated by phytoplankton during photosynthesis.  However, there is an upper limit to the phytoplankton population and once that limit is reached an excess of ammonia could accumulate.  We designed this study to exceed the total ammonia nitrogen (TAN) uptake capacity of a standard catfish pond.  We stocked a single ¼-acre pond with 6000, 12000, 18000, 24000, 30000, and 36000 hybrid (Ictalurus punctatus x I. furcatus) catfish per acre and analyzed feeding, growth, production, and water quality of these ponds using linear regression.

Catfish feeding and size decreased significantly as stocking densities increased, with fish at the 36K density consuming 17% less feed than the 6K density and weighing 21% less on average.  Survival (%) and food conversion ratio (FCR) was not different among stocking rates and net production increased by 782 lbs/acre with every increase of 1000 catfish/acre.  There was not an accumulation of TAN (mg/L) among the treatments.  However, nitrite-nitrogen increased by 0.027 mg/L and nitrate-nitrogen increased by 0.101 mg/L for every increase of 1000 catfish per acre.  Estimates of nitrification also increased significantly with higher stocking densities.  These data suggest that with enough time and available nitrogenous waste, populations of nitrifying bacteria will become large enough to process excess ammonia and nitrite.