Occurrence of Daily Growth Rings in Otoliths of Young-of-the-Year Flathead Catfish

Michael D. Brown and Dana L. Winkleman
Oklahoma Cooperative Fish and Wildlife Research Unit, 404 Life Sciences West, Oklahoma State University, Stillwater, OK 74078, (405) 744-6342, (405) 744-5006, danaw@okstate.edu

The sagittal otoliths of young-of-the-year flathead catfish Pylodictis olivaris were examined for the presence of daily growth rings. Fifty-nine individuals measuring from 38 mm to 150 mm total length were collected during daylight hours using boat electrofishing. An otolith from each specimen was glued to a microscope slide and lightly sanded and polished until the rings became visible at 400X magnification. Plotting the radii of the otoliths against the fishes' total lengths revealed a linear relationship. We are currently engaged in two experiments to validate whether the rings are deposited daily. We are marking otoliths with oxytetracycline hydrochloride and aging known-age fish. If otoliths from young-of-the-year flathead catfish can be aged, they may provide important information for flathead catfish biology and management, such as age, growth hatching dates, and mortality.