Circuli development on body scales of young pond-reared walleye (Stizostedion vitreum)

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Abstract
The development of circuli on the scales of young walleye were related to fish size and age. The species first develop scales in the caudal peduncle region of the body when the fish are approximately 30 mm in total body length and about 36 days old. Scale growth and circulus formation are directly related to body growth, with maximum deposition occurring in late July and early August. Seldom are circuli continuous ridges surrounding the scale focus; rather the number of lateral and central circuli are dependent on scale shape, body size, and time. The distances between respective circuli of all age groups examined were relatively constant except for a progressive increase in intercircular spaces between the first four circuli of fish aged 36–64 days. Within each age group the mean intercircular distances between the first 10 to 12 circuli tended to decrease with distance from scale focus. Cteni develop on caudal scales when scales have four to five circuli and when walleye are about 6 weeks of age.