We used inorganic fertilizer in three ponds at the Minor Clark Fish Hatchery and compared results with three ponds treated with a traditional combination of organic and inorganic fertilizer. Organic augmentation resulted in significantly higher water concentrations of chlorophyll a (16 vs. 7 µg L−1), total P (167 vs. 89 µg L−1), SRP (9.3 vs. 6.6 µg L−1), and inorganic nitrogen (230 vs. 184 µg L−1). Secchi depth and DO (7.9 vs. 11.2 mg L−1) were lower in the organically fertilized ponds. No filamentous algal blooms occurred in any ponds. Rotifers were the predominant zooplankton in all ponds; but traditionally fertilized ponds had greater copepod biomass. Fish survival (37%) and yield (36 kg ha−1) in inorganically fertilized ponds were much lower than previously found at Minor Clark Hatchery (about 90% survival). Although use of inorganic fertilization alone may reduce fertilizer and supplemental aeration costs in some hatcheries, it did not offset lost fish production in this study.
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Vol. 70 • No. 2