Evidence from previous studies of the rings on bone structures of fish indicates that in a number of species they are true year marks. Among the species of fish to which this method has been applied is the channel catfish. In order to determine the possibility of computing growth during successive years of life by means of bone markings, the left pectoral spines were collected from 204 channel catfish from Grand Lake, Oklahoma. These spines were cut in cross-section near the base, and the radii of the several growth fields and of the entire spine were measured with a micrometer mounted on a binocular microscope. These measurements revealed a high coefficient of co?relation (r = 0.969) between body length and spine radius.The straight line fitted to the measurements of fish length and spine radius for 187 fish had an intercept of --3.24 millimeters of fish length. Since this intercept is zero for all practical purposes, growth calculations were made by direct proportion. Both the method of aging and calculating growth of channel catfish appear to be satisfactorily accurate, since (1) the number of spine rings increases as the average length of the fish increases; (2) the calculated length of age-group II at the end of the secon.d year of life slightly exceeds the measured length of age-group I at the time of capture, and the growth to the third annulus of age-group III slightly exceeds the measured length of age-group II when captured in August; and (3) the markings on the pectoral spines of 50 channel catfish of known age corresponded to the markings as read on the spines collected from Grand Lake.
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