The aim of this study was to determine the effects of different soy protein concentrate (0, 15, 30, and 45%), defatted soy flour (0, 10, 20, and 30%), and wheat flour (10, 20, and 30%) contents replacing fish meal on physiochemical properties of extruded aquatic feed by using a twin screw extruder. The moisture content, barrel temperature, die diameter, and screw speed were adjusted to 45%, 137oC, 4 mm, and 250 rpm, respectively. With the higher amount of soy protein concentrate replacing fish meal, the expansion ratio, swelling ratio, and water stability increased significantly while specific length and water holding capacity decreased significantly. With the increasing defatted soy flour content, expansion ratio increased significantly, but specific length, water holding capacity and water stability decreased significantly. With increase in the wheat flour content, the specific length significantly decreased while the water stability significantly increased. In conclusion, aquatic feed quality was optimized in this study and could be used in the future.

The aim of this research is to evaluate the impact of various process conditions on the physical properties and digestibility of extruded fish feed at different barrel temperatures (120, 130, and 140oC) and moisture contents (35, 40, and 45%). The expansion ratio decreased with increasing the moisture content. The hardness was negatively correlated with the expansion ratio. The bulk density decreased by increasing moisture content. The water holding capacity increased by increasing the moisture content and barrel temperature. Soaking time significantly (p<0.05) affected water stability and the best water stability was observed in all samples soaked for 1 h, but water stability was also stable at 2 h and 3 h. There was a significant increase in the protein digestibility of extruded fish feed, compared to that of the raw material.