Effect of initial size on subsequent growth and carcass characteristics of divergently selected channel catfish.

Two experiments were conducted simultaneously to determine (1) if fast-growing fingerlings of channel catfish, Ictalurus punctatus, could be identified by simple visual selection of body size and (2) if initial size advantages influenced subsequent growth and carcass traits of divergently selected channel catfish. Exp. 1 included large (L), medium (M), and small (S) fingerling sizes from each of the control (C), selected upward (+) and selected downward (-) lines for body weight. Exp. 2 included all fmgerlings of the same size (25±5 g) from the 3 lines. Catfish from the L size-class, within each full-sib family in each line, were consistently heavier and longer than M and S size-classes throughout the 53-week experimental period. Fingerlings from the M size-class were also superior in growth to those from the S size-class. Catfish from the + line exceeded those from the C and -lines in body weight and total length at the conclusion of Exp. 1 but not in Exp. 2. This was attributed to the selection of equal size fmgerlings in Exp. 2 which may have excluded fingerlings with the best growth potential from the + body weight line. Results of the two experiments combined indicated that one generation of divergent selection has created genetic differences among lines of channel catfish.