Effects of replacing plant proteins with rubber seed meal on growth, nutrient utilization and blood biochemical parameters of tilapia (Oreochromis niloticus × O. aureus)

An 8-week feeding trial was conducted to evaluate the effects of replacing plant proteins with rubber seed meal (RSM) on growth, nutrient utilization and blood biochemical parameters of juvenile tilapia (Oreochromis niloticus × O. aureus). Five experimental diets were formulated with 0, 65, 130, 195 and 260 g kg⁻¹ RSM replacing graded levels of a mixture of plant proteins, respectively. Dietary RSM inclusion level up to 260 g kg⁻¹ did not affect growth and feed utilization. Fish fed diets with 65–130 g kg⁻¹ RSM showed the highest feed efficiency ratio and protein efficiency ratio. However, high inclusion of RSM (260 g kg⁻¹) markedly reduced the hepatic protease, lipase and amylase activities, and thereby decreased the dry matter and crude protein digestibilities. Similarly, plasma superoxide dismutase and glutathione reductase activities were depressed by high inclusion of RSM. These results indicate that dietary RSM inclusion level up to 195 g kg⁻¹ did not affect the growth and health status of tilapia, whereas a further inclusion of RSM might result in reduced feed digestibility and antioxidant capacity of tilapia.