Abstract
Walleye (Sander vitreus) fingerlings (30 to 35 mm) are commonly reared in ponds filled with surface (i.e., lake) water, but the use of ground (i.e., well) water would provide increased biosecurity. We assessed the potential for using well water to rear walleye by comparing plankton and water quality over 30 days between organically fertilized lined ponds that were filled with either unfiltered lake or well water. All ponds were inoculated with plankton that originated from Blue Dog Lake, filled by May 15, 2020, and remained fishless. Zooplankton density and body size were consistently reduced in well ponds suggesting that fry survival and growth would be reduced. Initially, well ponds exhibited higher ammonia-nitrogen and alkalinity, but lower pH owing to the inherent chemistry of the well water. Later, reduced ammonia-nitrogen combined with increased dissolved oxygen and pH suggest that decomposition of the organic fertilizer occurred slower in well ponds. A phytoplankton bloom was successfully initiated but was difficult to maintain despite consistently lower zooplankton density in well ponds. While the use of well water would enhance biosecurity, these data suggest that walleye fingerling production would be reduced relative to lined ponds filled with productive, lake water. Increasing organic fertilizer, supplementing with liquid 28N:0P:0K, and/or filling ponds earlier (e.g., 30 days) may provide a more favorable environment for walleye culture in lined ponds filled with well water.
Highlights
Surface waters have historically been used to fill ponds for rearing walleye (Sander vitreus) fingerlings at many locations (Summerfelt et al, 1996)
Increasing organic fertilizer, supplementing with liquid 28N:0P:0K, and/or filling ponds earlier (e.g., 30 days) may provide a more favorable environment for walleye culture in lined ponds filled with well water
Lined ponds filled with unfiltered water from either lake or well sources and fertilized with organics exhibited differences in zooplankton, water quality, and chlorophyll-a
Summary
Surface waters have historically been used to fill ponds for rearing walleye (Sander vitreus) fingerlings at many locations (Summerfelt et al, 1996). Surface waters provide nutrients (Rogge et al, 2003) and plankton that can solely support walleye production (Harding & Summerfelt, 1993) or in most cases, initiate a food web which is enhanced by fertilization (Culver, 1996; Summerfelt et al, 2011). Organic fertilizers provide immediate nourishment for zooplankton (Barkoh & Rabeni, 1990) and release nutrients during decomposition (Boyd & Tucker, 2014). The decomposition process reduces dissolved oxygen (Qin & Culver, 1992; Soderberg, 2012) and pH (Boyd & Tucker, 2014). Walleye initially consume zooplankton, which remain important in their diet for at least the first 21 days of pond culture (Summerfelt et al, 2011; Briland et al, 2015)
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