Abstract:GWT is an ingredient blend mixing vital wheat gluten, wheat flour and taurine with the ratio of 77.5%, 20.5%, and 2.0%, respectively. This study was conducted to evaluate GWT as a protein source to compare with low-temperature dried fish meal (LT-FM) and soy protein concentrate (SPC) in extruded practical diet to feed to juvenile giant croaker (Nibea japonica) and black sea bream (Sparus macrocephalus). Plasma biochemical indices and liver anti-oxidative indices of the two fish species were tested as fish health indicators in this study. Eight diets had been formulated, including a control diet with LT-FM (20%) and SPC (21.4%), six diets with decreasing percentages of LT-FM or SPC replaced by GWT (replacing levels were 33.3%, 66.7% and 100%, respectively, on protein basis) and one diet with both 50% of LT-FM and SPC was replaced by GWT. Each diet was fed to triplicate tanks of giant croaker with an initial weight of (12.83±0.91) g (26 fish per tank) and black sea bream with an initial weight of (15.40±0.02) g (35 fish per tank). All fish were reared in a sea-water flow-through system for 59 days. The results showed that there was no significant effect of replacing LT-FM by GWT on total protein (TP) content, plasma triglyceride (TC), and MDA content and liver SOD activity in giant croaker (P>0.05). However, total cholesterol (TG) and glucose (GLU) contents in plasma were significantly decreased (P<0.05), whereas the plasma SOD activity of juvenile giant croaker increased significantly (P<0.05) when 66.7% and 100% of dietary LT-FM was replaced by GWT. Partial or total replacement of LT-FM or SPC by GWT had no significant effect on plasma levels of TP, TG, TC and GLU, liver MDA content and plasma SOD activity of black sea bream (P>0.05). In contrast, significant increase of liver SOD activity was found when total LT-FM, 33.3% and 66.7% of SPC, and 50% of LT-FM and SPC in both were replaced by GWT in diet of black sea bream. To conclude, giant croaker was more sensitive than black sea bream to the significant reduction of LT-FM in the low fish meal based diet, with the changes of plasma biochemical indices and liver anti-oxidative indices. Highlights of the present study: firstly, it is the first study using GWT as main protein source in extruded diets for giant croaker and black sea bream; secondly, a low fishmeal (20%) containing extruded practical diet was used as the control.
