Multiple, low-dose copper sulfate pentahydrate treatment effects on water quality and bacterial, phytoplankton, and zooplankton communities in catfish aquaculture ponds
Bradley M Richardson, Charles C Mischke, Caitlin E Older, Monica L Wood, Cynthia Ware, Ambika Tiwari, Manoj Chandy Koshy, John W Lowe, Geoffrey C Waldbieser, Matt J Griffin, David J WiseAbstract
Objective
In U.S. catfish aquaculture, copper sulfate pentahydrate (CSP; CuSO4·5H2O) is used for a wide variety of applications, including the control of blue-green algae, pathogenic bacteria, and parasite hosts. However, information on the pondwide effects of multiple low-dose treatments is lacking. Herein, the influence of repeated, low CSP doses (0.5, 1.0, and 1.5 mg/L) on water quality, phytoplankton, zooplankton, microbial populations, and fish production were evaluated.
Methods
In March 2022, experimental ponds (0.31 ha) were stocked with Channel Catfish Ictalurus punctatus (8,000 fish/pond) and, beginning July 21, were treated with CSP doses for four consecutive weeks. Samples were collected before the first treatment and then taken weekly until harvest on October 13, 2022. Chlorophyll-a, total ammonia-N, nitrite-N, and total oxidized nitrogen and nitrate-N were determined; major phytoplankton taxa identified; zooplankton communities assessed; and microbiota evaluated by 16S ribosomal RNA gene (V4 region) sequencing.
Results
As expected, the CSP treatments significantly influenced the phytoplankton communities, reducing Cyanophyta by 67–86% (P = 0.011). Chlorophyta also showed declines based on pond treatment (P < 0.001). However, all of the copper treatment groups were dominated by green algae following treatment relative to control ponds, which remained blue-green dominated. Phytoplankton populations persisted throughout the study, even in the highest treatments, and oxygen depletions were not observed. At harvest, there were no differences among treatments in total feed fed, fish size, yield, or feed conversion ratio. All of the copper treatments significantly reduced chlorophyll-a concentrations, but all other water quality parameters remained similar. Furthermore, CSP appeared to stabilize the microbial communities. Control and 0.5-mg/L treatments had temporary fluctuations (unweighted UniFrac distances > 0.65), whereas 1.0- and 1.5-mg/L treatments were relatively stable over time (unweighted UniFrac distances < 0.55).
Conclusions
Collectively, the data suggest that repeated, low-dose CSP treatments, suitable for management of algae and trematode host snails, resulted in no detrimental changes in catfish aquaculture pond environments or production results. The treatments showed a stabilizing effect in the microbial community and shifted ponds toward the dominance of green algae rather than cyanobacteria, a source of off-flavor in catfish production.