Effect of stocking large channel catfish in a biofloc technology production system on production and incidence of common microbial off-flavor compounds

Authors: Green, Bartholomew - Bart; Schrader, Kevin

Submitted to: Journal of Aquaculture Research and Development
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/19/2015
Publication Date: 2/15/2015
Publication URL: http://doi.org/10.4172/2155-9546.1000314
Citation: Green, B.W., Schrader, K.K. 2015. Effect of stocking large channel catfish in a biofloc technology production system on production and incidence of common microbial off-flavor compounds. Journal of Aquaculture Research and Development. 6:314. Available:http://dx.doi.org/10.4172/2155-9546.1000314

Interpretive Summary: High yields are obtained from the biofloc technology (BFT) production system in response to high stocking and feeding rates 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. Stocker-size catfish, which weigh about a quarter of a pound, are being stocked increasingly by farmers in food-fish ponds so that harvested fish are within the size range preferred by processing plants. However, growth to market size of stocker catfish has not been evaluated in the BFT production system. Market-size catfish can be rendered temporarily unmarketable because they absorb from the water and accumulate “earthy” and “musty” compounds in their flesh. Geosmin and 2-methylisoborneol (MIB) are the respective compounds responsible for the “earthy” and “musty” off-flavors. Harvest delays caused by off-flavor episodes are a persistent problem for catfish farmers. We conducted a study to investigate the effect of stocking rate of stocker catfish on production and the incidence of “earthy” and “musty” off-flavors in the BFT production system. Results of this study showed that fish growth was density-dependent: the size of the fish at harvest decreased as the stocking rate increased. The total quantity of feed consumed by fish increased as the stocking rate increased, but the feed consumed by each individual fish decreased as the number of fish increased, despite all fish being fed to apparent satiation. Some unknown social interactions among fish was responsible for the reduced feed consumption by individual fish. The total production of fish increased with stocking rate because of the increasing number of fish. Total fish production was about 10-times higher than production from earthen pond culture. These results demonstrate that stocker catfish grow rapidly in the BFT production system at the stocking rates tested and attain sizes that meet processor needs. Concentrations of geosmin and 2-methylisoborneol in biofloc water were low throughout the study. All sampled fillets contained low concentrations of gesomin and 2-methylisobornel, but these fillets likely would not be deemed as having objectionable, if any, “earthy” or “musty” off-flavors by trained processing plant flavor testers because of the low concentrations present. The results of this study combined with data from our two previous studies provide strong evidence that the incidence of geosmin- and 2-methylisoborneol-related off-flavor episodes is low in the BFT production system.

Technical Abstract: Density-dependent production and incidence of common microbial off-flavors caused by geosmin and 2-methylisoborneol were investigated in an outdoor biofloc technology production system stocked with stocker-size (217 g/fish) channel catfish at 1.4, 2.1, or 2.8 kg/m3. Individual weight at harvest ranged from 658-829 g/fish and was inversely related to stocking density. Net fish yield ranged from 3.8-5.4 kg/m3, and increased linearly as stocking density increased. The percentage of sub-marketable fish (< 0.57 kg/fish) increased linearly with increasing stocking rate. Mean total feed consumption increased linearly with stocking density, but feed consumed per fish was inversely related to stocking density. Feed conversion ratio did not differ significantly among treatments. Concentrations of geosmin and 2-methylisoborneol in biofloc water were low throughout the study. All sampled fillets contained low concentrations of geosmin and 2-methylisobornel, but these fillets likely would not be deemed as having objectionable “earthy” or “musty” off-flavors when evaluated by trained processing plant flavor testers because of the low concentrations present. Data from this study combined with data from our two previous studies provide strong evidence that the incidence of geosmin- and 2-methylisoborneol-related off-flavor episodes is low in the BFT production system.