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5 factor (K) calculated as WT x 105/TL3 (Ricker, 1975). Data obtained by a U.S. Fish and Wildlife Service sampling program in the same area from 1979 to 1985 were used to determine the maximum total length attained by channel catfish during their first growing season and to verify our aging of the age 0 life history stage. Because the lumen of the pectoral spine may erode the first, and possibly also the second annulus in spines of older individuals (Sneed, 1951; Marzolf, 1952, 1955), the maximum length attained by channel catfish in one growing season in the Green River was used to determine if the first annulus was present. If it was judged that the first annulus was not present (the back- calculated length at age one exceeded the 80 mm maximum attainable length for one growing season), one year was added to the age of the fish, and back- calculated lengths at consecutive annuli were shifted one year to reflect the true annual growth. We used sections exhibiting a true, first annulus to back- calculate the maximum length at the second annulus. If the back-calculated length at the second annulus exceeded this length (150 mm), it was assumed that the second annulus had been eroded by the lumen. In this case, two years were added to the age of the fish and the back-calculated lengths at consecutive annuli were shifted two years to reflect the true annual growth. A back-calculated length at age 1 of greater than 80 mm would then indicate that the first annulus had been eroded, and a back-calculated length at age 2 greater than 150 mm indicated that both the first and second annuli had been eroded. We made no further attempt to validate our aging method because of the voluminous literature on aging channel catfish from spines (reviewed by Carlander, 1969).