An Evaluation of the Effect of Treatments for Pond Water Reuse on Zooplankton Populations

Abstract

Reuse of pond water is becoming more common in the culture of baitfish and hybrid striped bass (female white bass Morone chrysops × male striped bass M. saxatilis). Water conservation is important because of declining aquifer levels and increasing demand for groundwater. One challenge to this practice is the presence of predaceous copepods in pond water held from previous production operations (old water), which results in variable larval fish survival and fingerling production. This study evaluated methods of restarting zooplankton succession in old water. The concentrations of cladocerans, adult copepods, copepod nauplii, and rotifers from untreated old water, chemically treated old water (0.25 mg of the active ingredient Dylox per liter), mechanically treated old water (i.e., water filtered through a 60-μm screen with a drum filter), and ponds filled with new well water were compared. All ponds were fertilized twice a week with cottonseed meal and inorganic liquid fertilizer (10:30 [N:P]). Ponds with chemically treated old water had significantly more copepods than those subjected to the other three treatments. Ponds with mechanically treated old water had the highest bloom concentration of copepod nauplii. Ponds with chemically treated old water and mechanically treated old water had more rotifers than ponds with new well water or ponds with untreated old water. Mechanical filtration improved old water most in terms of both increased rotifer concentrations and reduced adult copepod concentrations within the first 2 weeks of pond treatment. Treating with mechanical filtration should be considered as an alternative to treatment with Dylox.