Effect of Organic and Inorganic Fertilizers on Plankton Production and Bluegill Bream Carrying Capacity of Ponds

Abstract
Small, excavated ponds were stocked with one‐year‐old bluegill bream (Lepomis macrochirus) in May, 1936, and drained in November. The number and total weight of fish in each pond were determined. Different ponds were fertilized with an inorganic fertilizer, laying mash, cottonseed meal, and cottonseed meal and superphosphate. Water samples were taken from each pond at intervals of two weeks throughout the season for quantitative and qualitative plankton determinations. An unfertilized control pond had the lowest average plankton production and the lowest carrying capacity for bluegill bream. The pond fertilized with cottonseed meal alone had the next lowest average plankton production and the next lowest carrying capacity. The pond fertilized with laying mash produced an average plankton yield about one and one‐half times as great as that fertilized with cottonseed meal, and the increase in carrying capacity for bluegills was of the same magnitude. Adding superphosphate to the cottonseed meal doubled the average plankton production and almost doubled the carrying capacity for bluegill bream. An inorganic fertilizer proved best, producing the greatest amount of plankton and fish. When inorganic fertilizers were used the entire food supply of the pond was dependent upon the production of phytoplankton but when organic fertilizers were used, they were partly utilized directly by animal organisms and the phytoplankton phase was more or less omitted. Consequently, organic fertilizers may produce the same fish yields as inorganic fertilizers but at lower levels of plankton abundance.

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