Analysis of pellet degradation of extruded high energy fish feeds with different physical qualities in a pneumatic feeding system

The aim of the present study was to investigate degradation of three commercial high energy extruded salmonid feeds, differing in physical quality, during pneumatic conveying in a feeding device at different airspeeds (25,30 and 35 m s(-1)) and feeding rates (9, 18 and 36 kg min(-1)). The physical quality of the feeds, with a diameter of 12 mm, was measured as existing quality, DORIS value, hardness and durability index. Significant differences in the formation of small particles among the feeds were observed during pneumatic conveying. Increasing air speed (m s-1) increased the formation of fractures (particle size 2.4-10 mm) and fines (particle size < 2.4 mm). Increasing the feeding rate (kg min(-1)) had the opposite effect, causing a reduction in formation of fracture and fines. Despite the significant differences in physical quality among the diets, no good correlations were found between physical quality parameters and pellet degradation during pneumatic conveying. DORIS value, hardness and durability index could therefore not be used to predict the degradation of pellets during pneumatic conveying. The overall conclusion from the experiment was that the three feeds varied in degradation pattern during pneumatic conveying, and the pellet degradation was highest at high airspeed and at low feeding rate. None of the measured variables for physical feed quality could be used to predict the pellet degradation pattern in the feeding system. (C) 2010 Elsevier B.V. All rights reserved.