Riboflavin is synthesized by all plants and many microorganisms, but not by animals. Riboflavin functions in the form of coenzymes flavin mononucleotide (FMN) and flavin adenine dinucleGtide (FAD). These coenzymes function as prosthetic groups of oxidation-reduction enzymes that are needed for the degration of pyruvate, fatty acids and amino acids. They are also involved in the electron transport system. Riboflavin incurs high losses during feed processing and prolonged exposure to sunlight, and is very soluble in water. Deficiency symptoms include anorexia, poor growth, abnormal swimming behavior and mortality. Sources of riboflavin include dried distillers solubles, fish meal, fish solubles, liver meals and yeast. Recommended supplementation level for riboflavin in commercial feeds is 40 mg/kg (Akiyama et al., 1992).