Families of channel catfishIctalurus punctatusof the 1982 and 1983 year classes were maintained in separate ponds. Fish from 4 to 26 months of age were evaluated for weight, length, and sex during seven sampling periods. Sex did not influence the growth of fish weighing less than 50 g at 10 months of age. Subsequently, sex had an increasing influence with increasing age: by 26 months, males were 37% heavier and 10% longer than females. Fish whose sex was reversed from male to female with steroid hormones grew like normal females through the time of sexual maturity. Growth and reproductive characteristics were typical of the phenotypic sex rather than of the genotype. Monosex populations of male channel catfish could increase production in commercial aquaculture operations.