Factors Affecting Cannibalism by Pond-Reared Juvenile Walleyes

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Abstract
Field and laboratory studies provided information concerning the onset, development, and possible control of cannibalism by pond-reared juvenile walleyes (Stizostedion vitreum) longer than 30 mm. Cannibalism began in early summer and was associated with increases in length ranges. Cannibal walleyes were the largest, and their prey the smallest, fish in field collections; cannibals had a higher growth rate, which led to the appearance of bimodal length-frequency distributions in samples collected in late summer and early autumn. In laboratory experiments, cannibalism did not occur in aquaria containing juvenile walleyes and fathead minnows (Pimephales promelas). Cannibalism was most frequent in aquaria that contained only walleyes and intermediate in frequency in aquaria that contained zooplankton and walleyes. Cannibals in the walleye-only aquarium consumed 6-33%/d of the fish present, and 41% of the vulnerable walleyes overall; when zooplankton were present, losses to cannibalism dropped to 28%....