A single-screw laboratory extruder was used to conduct an L 18 (2 2 X 3 6 ) Taguchi fractional factorial study of aquafeed processing. The ingredients were based on a formulation for nutritionally-balanced Nile tilapia diets containing distillers dried grains with solubles (DDGS) and soybean meal as the main protein sources, in addition to constant amounts of corn flour, whey, and fish meal. The effects of three levels of DDGS (20, 30 and 40%), soybean meal (30, 40 and 50%), ingredient moisture content (20, 30 and 40% db), screw speed (100, 150 and 200 rpm), barrel temperatures (80-100-100°C, 80-120-120°C and 80-140-140°C), and die dimensions (L/D ratios of 5, 9 and 13), and two levels of screw configuration (compression ratios of 2:1 and 3:1) on extrudate physical properties (moisture content, water activity, color, bulk density, unit density, pellet durability index, expansion ratio, water stability, water absorption and solubility indices) and extruder processing parameters (resulting temperatures, extruder torque, die pressure, mass flow rate, and specific mechanical energy) were determined. Data from raw materials, processing conditions, and extrudate properties were used to develop surface response curves and equations. However, predominantly low R 2 values (< 0.5) only permitted linear relationships between some independent parameters and response variables. Regarding main effects, die pressure significantly decreased with higher DDGS levels, moisture content, temperature, lower die L/D, and higher screw compression. Significant differences in color were caused by changes in DDGS levels and moisture content. Expansion ratio decreased significantly with higher moisture content and lower die L/D. In summary, DDGS, moisture content, die dimension, and the extruder had the biggest impact on most of the extrudate physical properties and processing conditions. Different combinations of these independent factors can be used to achieve desired extrudate physical properties and processing conditions.