Evaluation of Vital wheat gluten as a source of protein in extruded diets for juvenile Giant croaker (Nibea japonica) : feed technological properties and biological responses

M-AA

English. The aim of present study was to evaluate Vital wheat gluten (VWG) as protein source in comparison with high-quality fish meal (LT-FM) and soy protein concentrate (SPC) in extruded diets for juvenile Giant croaker (Nibea japonica). An ingredient blend named GWT was prepared by mixing the VWG, wheat and taurine with the ratio of 77.5%, 20.5% and 2.0%. The dietary treatments consisted of a control diet (V0) based on LT-FM (20%) and SPC (21.4%), six diets (VF1, VF2, VF3, VS1, VS2 and VS3) in which the LT-FM or SPC had been replaced by the GWT at the levels of 1/3, 2/3 and 100%, respectively, and one diet (VFS) which jointly replacing 50% proteins from LT-FM and 50% proteins from SPC by proteins of GWT.Extrusion parameters were recorded and discussed, the physical quality of feed pellet were also determined. A trend of increased expansion with both increased proportion of FM replaced by VWG, and with increased proportion of SPC replaced by VWG were found. Each diet was fed to triplicate tanks of 11-g Giant croaker reared in a sea water flow through system at 28℃ for 59 days. The results showed that no significant impact on weight gain (WG), whole body composition and apparent digestibility coefficients (ADC) of individual AA and total AA were found when the LT-FM had been gradually replaced by GWT from 0 to 100% (P > 0.05). Feed intake (FI) and feed conversion ratio (FCR) were significantly increased and retentions of N and energy were significantly decreased with the increasing GWT inclusion (P < 0.05). No significant effect were seen in whole body composition except for ash content and energy retention when the SPC was gradually replaced by GWT from 0 to 100%. Retention of N and ash content were significantly decreased for all replacement of dietary SPC with GWT. Quadric relationships were found in both FI and WG with increasing GWT inclusion. The ADC of total AA was increased with GWT inclusion, and a linear increase of ADC of Cys was also observed. Crude fat content and gross energy in whole body and retentions of N and energy were significantly decreased when both 50% of LT-FM and SPC were replaced by GWT, but the FI and WG were not significantly affected. To conclude, in extruded practical diet for Giant croaker with both 20.0% inclusion of high quality fish meal and 21.4% inclusion of SPC, one third of the high quality of dietary fish meal or 65% of the SPC can be safely replaced by the taurine supplemented mixture of vital wheat gluten and wheat flour without causing any adverse effect on feed intake, growth rate, feed conversion, whole body compositions, and retentions of N and energy.