Comparison Study on Utilizing Crystalline or Coated Methionine by Tilapia (Oreochromis niloticus O. aureus)

The present study was conducted to compare the ability of utilizing crystalline and coated methionine (Met) in diet of tilapia (Oreochromis niloticus O. aureus). Four diets with iso-lipid and iso-nitrogen were designed as fish meal diet (FMD, 9% fish meal), non-fish meal diet (NFMD, 0% fish meal), crystalline Met diet (Cr-Met) and coated Met diet (Co-Met) with crystalline Met or coated Met addition in NFMD to obtain the same Met level as FMD. Tilapia with initial body weight of (1.22 0.07) g was fed the four diets for 8 weeks. The results showed that weight gain (WG) of the four groups were 1642.7%, 1250.3%, 1362.0% and 1451.7%, feed conversion rate (FCR) were 1.08, 1.45, 1.30 and 1.21, respectively. Compared with NFMD group, WG increased by 8.9% and 16.1% (P0.05), and FCR decreased by 10.34% and 16.55% (P0.05) by the addition of crystalline or coated Met in diet. Liver glutamic-pyruvic transaminase (GPT), glutamic-oxaloacetic transaminase (GOT) activity peak appeared at 2h and 4h after ingesting for fish in FMD and NFMD groups, which was advanced to 1h after ingesting for Cr-Met group, and delayed to 5h after ingesting for Co-Met group. The Plasma GOT, GPT activity had a similar variation trend to that of livers. The digestive trial showed that fish of fed FMD had the highest, and which of fed NFMD had the lowest digestibilities of dry matter (DM) and crude protein (CP). Compared with NFMD group, DM and CP digestibilities were significantly improved by the addition of crystalline Met and coated Met in diet. These results showed that the growth and nutrients digestibility of tilapia could be improved by adding crystalline Met and coated Met in practical diet deficient in Met. Tilapia can utilize coated Met more efficiently than crystalline Met.