Physical properties of extruded fish feed with inclusion of different plant (legumes, oilseeds, or cereals) meals

A study was undertaken to evaluate the effect of various ingredients on the physical quality of fish feeds. Eleven fish meal-based diets, formulated to have the same levels of macronutrients, differing in either starch or protein source, were processed in a five section twin-screw extruder. The purified starch, added to reach the nutritional specifications of the diets, was significantly correlated to expansion (r = 0.405, P<0.001), durability (r = 0.276, P=0.012), and hardness (r = 0.494, P<0.001), while such correlations were not seen for the total starch level in the diets. Cellulose, added as filler to reach the same level of NSP in the diets, was negatively correlated to the expansion (r = −0.603, P<0.001). The specific mechanical energy of the extrusion process was weakly correlated to starch gelatinisation (r = 0.220, P<0.019). The present study showed that traditional parameters and classifications such as chemical composition of plant ingredients are inadequate indicators of processing effects when used in fish diets. The overall conclusion is that processing parameters needed to achieve the desired physical properties of diets, should be based on specific knowledge of each ingredient in the feed.