Organic and Mixed
Organic–Inorganic Fertilization of Plastic-Lined Ponds for Fingerling
Walleye Culture
M.L. Rogge, A.A. Moore, J.E. Morris-2003
North American Journal of Aquaculture, 65(3):
179–190
Abstract:
Treatment with organic fertilizer was compared with
treatment involving a mix of organic and inorganic fertilizers for culture
of walleye Stizostedion
vitreum fingerlings in 0.04-ha plastic-lined ponds. Organic
fertilization consisted of weekly additions of alfalfa and cottonseed
pellets. Each type of organic fertilizer was applied to each pond at 2.3
kg/week. Nitrogen (36–0–0 as N–P–K) and phosphorus (12–49–6)
fertilizers were used weekly to adjust the ratio of nitrate-nitrogen to
total phosphorus ratios in the mixed-fertilizer treatment to 7:1. Nutrient
values in ponds treated with organic fertilizer were similar to those in
ponds treated with the organic–inorganic mix. However, the water used to
fill the ponds was initially high in both nitrogen and phosphorus, which may
have reduced the nutrient differences between treatments. There were also no
differences in food base densities (zooplankton and benthos) or fingerling
production between treatments. Concentrations of dissolved oxygen at pond
bottoms were sometimes less than 1 mg/L in the morning in both treatments;
however, this had no apparent effect on fingerling survival in either
treatment. Daphnia
spp. and copepod populations sharply declined in both treatments after fish
were stocked, suggesting that larval walleyes immediately fed on these
crustaceans. Zooplankton populations remained low until near the end of the
season. Benthic invertebrate densities were high throughout the season in
both treatments and showed no differences between treatments. Stomach
content analyses revealed walleye fingerlings consumed Daphnia
spp. and copepods throughout the experiment, whereas dipteran larvae became
increasingly important once walleyes reached 20 mm, about 2 weeks into the
experiment. Both fertilization treatments produced relatively large fish
(0.57 g) with good survival rates (>50%). The results from this study
suggest that dipteran management is important for providing food items for
larval walleyes and that high initial nutrient levels from water sources may
reduce the requirements for inorganic enrichment in plastic-lined ponds for
walleye culture.
(Iowa State University, Department of Animal Ecology,
124 Science II, Ames, Iowa 50011, USA)