No abstract

The study was conducted to examine the effects of different methionine (Met) sources on the growth performance of channel catfish (Ictalurus punctatus). Six diets with isonitrogen and isoenergy were formulated as positive control (PC) diet (0.57% Met), negative control (NC) diet (0.42% Met) without or with the addition of crystalline DL‐Met (CM), Met hydroxy analogue (MHA), Met hydroxy analogue calcium salt (MHA‐Ca) and microcapsulated DL‐Met (MM) to obtain the same Met level as PC diet. After 8 weeks feeding trial, channel catfish (76.0 ± 0.3 g) fed MHA‐Ca and MM diets, but not CM and MHA diets, had higher weight gain, lipid productive value, protein productive value and lower feed conversion ratio than those in NC group (P < 0.05) and showed no differences in these indicators with PC group (P > 0.05). Levels of serum total protein and total free amino acid (TFAA) of all groups peaked at the 4th h, and CM group had lower TFAA level than that in MM group at the 6th h after feeding (P < 0.05). In NC group, the activities of liver aspartate aminotransferase and alanine aminotransferase peaked at the 4 h after feeding, and the peaking time in CM group was advanced to the 2nd hour, while in MHA, MHA‐Ca and MM groups, the peaking times were delayed to the 6th hour after feeding. The above results indicated that the supplementation of MHA‐Ca, MM rather than CM, MHA in diets deficient in methionine could improve the growth of channel catfish.

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.