Harvesting zooplankton with submersible pumps increases chlorophyta density and reduces cyanophyta and zooplankton population variability

Authors: MISCHKE, CHARLES - Mississippi State University; Richardson, Bradley; YAMAMOTO, FERNANDO - Mississippi State University; GOODMAN, PENELOPE - Mississippi State University; TIWARI, A - Mississippi State University; Wood, Monica

Submitted to: North American Journal of Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/16/2025
Publication Date: 11/18/2025
Citation: Mischke, C.C., Richardson, B.M., Yamamoto, F.Y., Goodman, P.M., Tiwari, A., Wood, M.L. 2025. Harvesting zooplankton with submersible pumps increases chlorophyta density and reduces cyanophyta and zooplankton population variability. North American Journal of Aquaculture. 88(1)49-63. https://doi.org/10.1093/naaqua/vraf028.
DOI: https://doi.org/10.1093/naaqua/vraf028

Interpretive Summary: Supplemental feeding of zooplankton to catfish fry may be beneficial for growth and nutrition. Catfish ponds provide high densities of zooplankton for on-site harvest, and harvesting zooplankton from these ponds may, in turn, provide other benefits to the pond. In this study, 8 experimental ponds were used to evaluate how harvesting zooplankton can influence other aspects of the pond. A submersible pump was placed in 4 ponds and used to flush water through a mesh bag. Zooplankton were continously collected for 4 days per week throughout the summer production season. Results showed that harvested ponds had higher densities of beneficial green algae, and less variability in blue-green algae and zooplankton density. This suggests that harvesting zooplankton from catfish ponds may provide a more stable and predictable environment for the organisms within the ponds, and the farmers that manage them. Thus, using zooplankton from the on-farm ponds may provide benefits to all parts of the catfish production cycle. This research supports the Secretary of Agriculture’s priorities to increase profitability of farmers.

Technical Abstract: Based on catfish fry zooplankton feeding preferences, nutritional value of zooplankton, and improved growth when fed zooplankton, supplemental feeding of zooplankton in the hatchery may be beneficial to producers. However, harvesting zooplankton from ponds may have cascading effects on the pond ecology including standing stocks of zooplankton, phytoplankton composition, and water quality. Herein the effects of zooplankton harvest on the pond community were determined. Eight 0.04 ha ponds, containing no fish, were selected. In 4 ponds, a 373W submersible pump was suspended in the water column and allowed to pump continuously for 4 days per week (harvest ponds) collecting zooplankton in 250 µm mesh bags; the other 4 ponds contained no submersible pump and were used as control ponds. The study was carried out over 20 weeks, representing a typical catfish fry-fingerling production season. Water was collected weekly to evaluate water quality and phytoplankton abundance. Samples from zooplankton tows were counted to estimate zooplankton abundance. Data were analyzed using generalized linear mixed effects models. There was no overall influence of harvest on phytoplankton or zooplankton abundance; however, sampling date and the interaction of harvest and sampling date were significant. Over time, Cyanophyta continually increased in control ponds but decreased in harvested ponds. Chlorophyta decreased in control ponds but slightly increased in harvested ponds. Zooplankton abundance increased throughout the summer, with harvested ponds typically having lower abundances, on average, than control ponds. Zooplankton abundance was also much more variable in control ponds, compared to harvested ponds. The results of this study show high harvest pressure resulted in phytoplankton and zooplankton population stabilization, particularly as the study moved further into the summer and communities were established. This shows promise as an effective method to harvest zooplankton for small-scale feed supplementation while improving the pond community by stabilizing Chlorophyta populations, reducing variance in zooplankton populations, and reducing the density of Cyanophyta.