Formation of Annuli in Otoliths of Bluegills

Hatchery-spawned bluegills Lepomis macrochirus were reared in controlled laboratory conditions to evaluate the effects of water temperature, photoperiod, and feeding rates on opaque and translucent band formation in otoliths. Opaque bands were associated with periods of slow growth, and translucent bands were associated with periods of fast growth. Marginal increments (translucent bands distal to opaque bands) formed at 22°C or higher water temperatures. Although opaque bands formed, no marginal increments formed when water temperature was below 22°C. Fish exposed to a cycle of warm water (≥22°C), cool water (<17°C), and warm water formed a second opaque band and marginal increment. Opaque bands and marginal increments formed in bluegill otoliths at similar temperatures in outdoor tanks, in two lakes, and in the laboratory. Opaque bands also were induced by changes in photoperiod and feeding rate; however, the effects of photoperiod and feeding rate were inconsistent, and the opaque bands formed were typically faint compared to those resulting from temperature changes. Bluegills spawned in May 1984 and held in outdoor tanks during September 1984–December 1985 formed an opaque band in their otoliths during February–June. The opaque band is considered a valid annulus for age-1 bluegills.