ARS | Publication request: Effect of stocking biomass on solids, phytoplankton communities, common off-flavors, and production parameters in a channel catfish biofloc technology production system

Submitted to: Aquaculture Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 5, 2012
Publication Date: N/A

Interpretive Summary: Catfish farmers increasingly are stocking production ponds with larger catfish fingerlings called stocker catfish. Stocker catfish typically weigh one-half to one-third of a pound each and are grown from small fingerlings stocked in earthen ponds. Large channel catfish have been grown in a more intensive production system called the biofloc technology (or mixed suspended-growth) production system, but not stocker catfish; net yield of large catfish from this system was more than ten times that obtained from an earthen pond. This high production in the biofloc technology production system is possible because a complex of living organisms, including phytoplankton and bacteria, closely associated with particulate organic matter that is maintained in suspension in the water column by continuous aeration metabolizes nitrogenous waste excreted by the intensively fed catfish. We conducted a study to determine the effect of three different fish stocking rates on production of stocker channel catfish, water quality, phytoplankton dynamics, and musty and earthy off-flavors in a biofloc technology production system. Stocker catfish averaging one-third of a pound were produced at all stocking rates. The total weight of stockers harvested increased linearly as the stocking rate increased, and net yields were four to five and one-half times greater than yields from traditional earthen pond culture. Initial phytoplankton populations were dominated by small colonial green algae and diatoms, and later transitioned to populations dominated by a small, filamentous cyanobacteria (blue-green algae) and diatoms. Low, variable concentrations of the off-flavor compounds 2-methylisoborneol and geosmin, odorous compounds that can accumulate in fish flesh and render them unmarketable, were present in biofloc tank water during most of the study and two tanks yielded catfish with 2-methylisoborneol or geosmin concentrations that might be classified as off-flavor. However, concentrations of these compounds were lower than those observed typically for catfish production in earthen ponds. This study demonstrated that the biofloc technology production system can be used to produce stocker channel catfish and that high rates of feed application were possible because algal uptake and bacterial transformation of nitrogenous waste excreted by fish limited its accumulation. Our increased understanding of the phytoplankton and water quality dynamics in response to continuous high feed input and how these may affect the prevalence and intensity of musty and earthy off-flavors will permit further refinement of this production system technology, which represents an alternative method that yields higher production than traditional pond culture.

Technical Abstract: The effect of initial channel catfish (Ictalurus punctatus, Rafinesque, 1818) fingerling biomass (1.4, 1.8, or 2.3 kg m-3) on phytoplankton communities, common off-flavors, and stocker catfish production parameters was evaluated in biofloc technology production tanks. Stocker catfish size (145.5 – 172.6 g fish-1) at harvest did not differ among treatments, but net yield increased linearly as initial biomass increased (R squared = 0.633). Mean total feed consumption increased linearly with initial catfish biomass (R squared = 0.656) and ranged from 10.7 – 15.8 kg m-3. Total suspended solids (TSS) in all treatments increased linearly with total feed addition, and high TSS appeared to impact negatively daily feed consumption. Initial phytoplankton populations were dominated by small colonial green algae and diatoms, and later transitioned to populations dominated by a small, filamentous cyanobacteria and diatoms. Low, variable concentrations of 2-methylisoborneol and geosmin were present in biofloc tank water during most of the study and two tanks yielded catfish with 2-methylisoborneol or geosmin concentrations that might be classified as off-flavor. One isolate of actinomycete was isolated sporadically from some biofloc tanks, but its abundance was not correlated with 2-methylisoborneol concentration in tank waters. The microbial sources of 2-methylisoborneol and geosmin in biofloc tanks remain unidentified.