Effects of Dietary Oligo-Methionine on the Growth Performance, Feed Utilization and Protein Metabolism Responses of Juvenile Large Yellow Croaker (Larimichthys crocea)

Abstract:

Enzyme-catalyzed synthesis of oligo-methionine (OMet) has been available, however, little is known on the application of OMet in aquatic feed. In this study, an 8 week feeding trial was conducted to investigate the effects of dietary crystalline methionine (CMet) and OMet on the growth performance, feed utilization and protein metabolism responses of juvenile large yellow croaker (Larimichthys crocea) with initial body weight of (26.0±1.6) g. A practical diet with low fish meal content (31.8%) was used as the control diet (LF). Six other experimental diets (CMet 0.35, CMet 0.65, CMet 0.95, OMet 0.35, OMet 0.65, and OMet 0.95) were formulated with 0.35%, 0.65% and 0.95% CMet or OMet respectively. The weight gain rate (WGR) of fish treated with OMet or CMet was significantly higher than control and increased significantly along with the elevated level of supplement (P<0.05). The WGR was the highest in fish treated with OMet 0.95. The WGR and protein efficiency ratio (PER) of fish in OMet treatment were significantly higher than those treated with CMet (P<0.05). In all treatments there was no significant difference in survival rate, feed conversion ratio or body composition (crude protein, crude lipid, ash, and moisture, P>0.05). Compared to CMet treatment, OMet caused lower hepatosomatic index (HSI) and higher activities of glutamic-oxaloacetic transaminase (GOT) and glutamic-pyruvic transaminase (GPT) in the liver (P<0.05). Meanwhile, the methionine level greatly affected activities of GOT. The fish in OMet 0.95 treatment showed the lowest HSI and the highest GPT and GOT activities. However, in all groups no significant difference was detected in the concentrations of ammonia and urea nitrogen in the serum (P>0.05). This study indicated that compared to CMet, OMet might be more effective in improving the growth performance and feed utilization of large yellow croakers, therefore could replace the former as the external methionine source to balance the amino acids in the soybean protein feed.