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In this study, five diets were formulated, namely positive control, negative control (lysine deficient) without or with the addition of crystalline L-LysÁHCl, L-LysÁH 2 SO 4 and microcapsulated L-lysineÁHCl (M-Lys), and then fed to channel catfish with an initial body weight of 76.0 AE 0.3 g to investigate the effects of various lysine sources on the growth. After 8-week feeding, the fish fed M-Lys diet, but not LysÁHCl or LysÁH 2 SO 4 diet, had a higher weight gain, a higher protein retention ratio and a lower feed conversion ratio than that fed negative control (P < 0.05), and showed a similar growth as positive control. The serum free amino acid level of LysÁHCl and LysÁH 2 SO 4 group reached the plateau at the 2nd h after feeding, while the other three groups peaked at the 4th h. In LysÁHCl and LysÁH 2 SO 4 groups, the activities of liver aspartate aminotransferase and alanine aminotransferase peaked at the 2nd h, but M-Lys group peaked at the 6th and 4th h after feeding, respectively. The above results indicated that the supplementation of M-Lys rather than LysÁHCl or LysÁH 2 SO 4 in lysine-deficient diet could improve the growth performance of channel catfish, due to the delayed absorption of supplemental lysine.

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