Immature fish often lack the ability to synthesize PL (Fontagne et al. 2000), so dietary PL are essential for growth, survival, feed utilization, or optimal health in some juvenile fish. Estimated dietary PL requirement for fry of most fish species is 1–3% of the diet (Coutteau et al. 1997). Larger fish may not benefit from dietary PL supplementation due to slower growth rates and the capacity to synthesize PL from dietary precursors (e.g., Poston 1990b, Niu et al. 2008). However, PL synthesis is a limiting factor for the development of other freshwater omnivorous fish such as the common carp (Geurden et al. 1999). Therefore, this study focused only on the juvenile life stage of channel catfish. Juvenile diets for channel catfish are used for a shorter duration than growout diets, and the cost of PL supplementation could be justified if measurable benefits could be documented in this species.