Effects of pelleted and extruded feed of different ingredients particle sizes on feed quality and growth performance of gibel carp (Carassius gibelio var. CAS V)

Ten diets with different processing methods (PF: pelleted feed and EF: extruded feed) and different ingredients particle sizes (104, 115, 163, 199 and 260 mu m) were examined for their physical characteristics and amino acid composition. This was followed by an 8-week feeding trial to gibel carp (Carassius gibelio var. CAS V) (mean initial weight: 7.11 +/- 0.05 g) to evaluate the effects of ingredient particle size and feed processing methods on their growth, feed efficiency, intestinal enzymes/ultrastructure and some plasma biochemical parameters. The results showed that EF had higher expansion ratio, water absorption index, starch gelatinization degree and bigger size of pores inside the granules while lower bulk density, hardness, water solubility index, amino acid and reducing sugar content than PF (P < 0.05). Feed processing (pelleting or extrusion) significantly affected feed color and PF obtained higher lightness and redness than that of EF (P < 0.05). Gibel carp fed on EF had significantly lower feeding rate than those fed PF (P < 0.05). Specific growth rate, feed efficiency and protein retention efficiency in EF groups were significantly higher than PF groups (P < 0.05). Gibel carp fed EF showed significantly higher intestinal trypsin, chymotrypsin, amylase, plasma total free amino acid and plasma glucose than fish fed PF (P < 0.05). The smallest ingredients particle size (104 mu m) resulted in significantly lower feed efficiency in gibel carp than other particle sizes groups (P < 0.05). Fish fed with the diets of 260 mu m ingredient particles displayed damaged or deformed microvilli than 104 and 163 mu m groups. In conclusion, extrusion processing improved feed quality and gibel carp growth performance. Large ingredient particle size negatively affected fish intestinal health. The optimal ingredients particle size for gibel carp was 163 mu m