Relationships between Turbidity, Piscivory, and Development of the Retina in Juvenile Walleyes

Abstract

We conducted laboratory experiments to determine relationships between water turbidity, piscivory, fork length, and development of the retina in juvenile walleyes Stizostedion vitreum. Walleyes 85 mm and longer ate a greater weight and number of fathead minnows Pimephales promelas in turbid water than in clear water. Feeding was inhibited at the highest turbidities (100 and 161 nephelometric turbidity units, NTU) in 1-h feeding trials but not at the highest turbidity (121 NTU) in 4-h trials. In contrast, walleyes in the shorter length-group (≤75 mm) fed at approximately the same rate in clear and turbid trials, but consumption was inhibited at the two highest turbidities (100 and 161 NTU) used in 1-h trials. The tapetum lucidum was present in the retina of walleyes used in all the experiments. Aggregation of photoreceptor cells in the retina into groups of 20 to 30 (to form macroreceptors) begins when walleyes are approximately 60 mm long. Macroreceptors are believed to increase acuity in dim light. In our experiments, the development of macroreceptors was related to increased feeding efficiency in turbid water. The development of scotopic vision early in life permits walleyes to exploit dimly lit environments not used by other predators.