CHANNEL CATFISH PRODUCTION IN A BIOFLOC TECHNOLOGY SYSTEM
High yields are obtained from an outdoor biofloc technology (BFT) production system in response to high stocking and feeding rates because the biofloc, which is maintained in suspension by continuous aeration, metabolizes excreted feed nitrogen (N). Penaeid shrimp and tilapia are grown in the BFT system because they can derive some nutrition from consuming the biofloc. For fish like the channel catfish (Ictalurus punctatus), which derives little or no nutrition from the biofloc, the BFT system is a water quality management tool that permits production intensification and increased water use efficiency. We investigated channel catfish production, water quality and phytoplankton dynamics, and common off-flavors in a series of production experiments conducted in outdoor, 18.6-m2 tanks.
Effect of stocking rate on fingerling to stocker (115-150 g/fish) production was evaluated. Survival averaged 95.1%. Fingerlings (48 g/fish) were stocked at 26, 35, 44 fish/m2 and grown for 183 days. Gross fish yield (GFY) increased linearly from 4.9 to 7.1 kg/m3 as stocking rate increased. Final weight (FW) averaged 172.6, 150.8, and 145.5 g/fish for the low to high stocking rates, and did not differ significantly. Growth of stocker catfish (217 g/fish) to market size was evaluated at stocking rates of 5.4, 8.1, and 10.8 fish/m2 in a 154-d study. Mean survival was 97.2%. GFY increased linearly from 5.2 to 8.2 kg/m3, but mean FW decreased linearly from 828.9 to 658.4 g/fish in response to increasing stocking rate. Fingerlings (49 g/fish; 12 fish/m2) were grown to market size in tanks subjected to three solids management protocols. Settling chamber influent flow rates were 0, 0.6, and 2.5 L/min. Solids removal significantly reduced total suspended solids from 662 to 290 mg/L, but did not affect fish production. Mean GFY and FW were 8.0 kg/m3 and 571 g/fish, respectively.
Operation of the BFT system during the cold season showed that catfish can be held with minimal weight loss, and in absence of sustained ammonia-nitrogen input that the biofloc retained its ability to biotransform ammonia regardless of whether phytoplankton or suspended solids predominated. An active biofloc at the beginning of the growing season obviates the start-up time to establish a new, fully functional biofloc and associated ammonia and nitrite spikes.
Fast-growing, unicellular and small colonial types of green algae, diatoms, and slower growing, small colonial types of cyanobacteria dominated phytoplankton communities. BFT culture tanks were susceptible to episodes of geosmin and 2-methylisoborneol (MIB) in the tank waters and subsequent bioaccumulation of these compounds in the catfish flesh. While levels of geosmin and MIB in the tank waters were less intense and less persistent than episodes that can occur in catfish aquaculture ponds, the microbial sources responsible for geosmin and MIB in BFT tanks remains unknown and requires additional research.