Apparent digestibility of protein, amino acids and energy in rainbow trout (Oncorhynchus mykiss) fed a fish meal based diet extruded at different temperatures

A fish meal/wheat flour based dry ingredient mix was extruded at three different temperatures (100, 125 and 150 °C), by varying extrusion conditions according to two different methods. Employing method 1, the temperature of the conditioner, torque, screw speed, pressure, feed rate and process water of the extruder were varied. Whereas in method 2, conditioner temperature and screw speed were kept constant, and the variation in process water input was restricted. The diets, which contained yttrium oxide as an inert maker, were fed to three replicate groups of rainbow trout. Feces for digestibility determination were obtained by stripping. The results showed that the differences in extrusion temperature caused no significant differences in apparent digestibilities of crude protein, individual amino acids or energy. The apparent digestibility of cysteine was significantly higher for diets produced by method 1 than by method 2.