Effects of solids removal on water quality and channel catfish production in a biofloc technology production system

Authors: Green, Bartholomew - Bart; Schrader, Kevin; McEntire, Matthew - Matt

Submitted to: Journal of Applied Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/20/2018
Publication Date: 10/25/2018
Citation: Green, B.W., Schrader, K.K., McEntire, M.E. 2018. Effects of solids removal on water quality and channel catfish production in a biofloc technology production system. Journal of Applied Aquaculture. 31(1):1-16. https://doi.org/10.1080/10454438.2018.1536010.
DOI: https://doi.org/10.1080/10454438.2018.1536010

Interpretive Summary: High concentrations of total suspended solids in the biofloc technology production system that result from the high feeding rates used to ensure rapid growth have been shown to affect adversely culture animal performance. Growth and yield were improved when settling chambers were used to reduce total suspended solids concentration in marine biofloc technology production systems, but their use has not been tested in an outdoor biofloc technology system used for growing channel catfish. The present study was conducted in an outdoor biofloc technology production system to address the effect of three solids management protocols on channel catfish production, the incidence and intensity of “earthy” and “musty” off-flavor in catfish fillets, and on water quality. Water was moved from each biofloc tank to its settling chamber by airlift pump at a low or high flow rate; no solids were removed in the control treatment. Concentrations of total suspended solids were maintained at or below the 400-ppm target concentration by both flow rates. Daily feed consumption by control treatment fish was limited once the total suspended solids concentration exceeded about 800 ppm. In contrast, daily feed consumption by fish in the low flow-rate tanks was independent of increasing total suspended solids concentrations while in the high flow-rate tanks daily feed consumption increased linearly with increasing total suspended solids concentrations. Despite these differences in daily feed consumption, no significant differences in production were detected among the three treatments at harvest. However, fish from the control treatment tanks were skewed towards the smaller size classes. Based on laboratory analysis, catfish fillets from the low and high flow-rate treatments would be designated as having an objectionable “earthy” off-flavor. Solids removal significantly reduced the nitrification rate, which is the microbial oxidation of ammonia to nitrate. Thus, it appears that total suspended solids concentration must be high enough to ensure rapid nitrification and to minimize the frequency and intensity of episodes of “earthy” and “musty” off-flavor in catfish fillets. Based upon our results, the optimum concentration, which needs to be determined through further research, appears to fall between 400 to 800 ppm total suspended solids.

Technical Abstract: Control of total suspended solids was evaluated in a channel catfish (Ictalurus punctatus) biofloc technology production system. Settling chambers flow rates were 0 (Control), 0.9 (LO) or 2.9 HI) L/min. Channel catfish yields (7.6-8.7 kg/m3) were not affected significantly when total suspended solids were reduced to 300 mg/L. Control treatment fish were skewed towards smaller size classes. LO- and HI-treatment fillet geosmin concentrations were high enough to be designated as off-flavor. Solids removal reduced water quality variables and nitrification rate, more so in the LO treatment. It appears total suspended solids concentration must be high enough to ensure rapid nitrification.