The Determination of Age and Rate of Growth from Vertebrae of the Channel Catfish, Ictalurus Lacustris Punctatus

Abstract

Age and rate-of-growth calculations were made from the fifth vertebrae of 535 channel catfish (Ictalurus lacustris punctatus) taken from Pool 9 of the upper Mississippi River at Lansing, Iowa. Vertebrae were collected during the summers of 1945 and 1946 and examined with the aid of a standard scale projector. They were prepared by removal of adhering material with a solution of pepsin and hydrochloric acid. Direct observation of the centra of the vertebrae revealed annular rings which were shown to be true year marks when checked by the usual tests of validity. In addition field samples were compared to fish of known age. Body-vertebra relationship was shown to be curvilinear and appropriate corrections were made in all calculations. Growth of catfish is slow throughout life and progresses at a uniform rate for a longer period than is characteristic of most fresh-water fishes. Growth is greatest during the second year of life and Leeˈs phenomenon is not apparent in calculations based on older fish. Growth increment in succeeding calendar years varied greatly but trends showed a striking resemblance to those of fresh-water drum taken from the same water during the same period. Body length-weight relation is expressed by a parabola with the formula log W = −4.2738 + 3.66 log L. A few catfish mature at a length of 12 inches but 100 percent of the fish are not mature until a length of 22 inches is attained. Sex ratio was 1.12 males to one female.