NUTRITIVE-VALUE OF GELATINIZED CORN MEAL AS A CARBOHYDRATE SOURCE TO GRASS CARP AND HYBRID TILAPIA OREOCHROMIS-NILOTICUS X OREOCHROMIS-AUREUS

The effect of extrusion on the nutritional value of corn meal for grass carp Ctenopharyngodon idella and hybrid tilapia Oreochromis niloticus x O. aureus fingerlings was studied. Raw and extruded corn meal were mixed in five proportions at a 50% level in the diet, with a gelatinized ratio (GR) ranging from 29 to 100%. The apparent starch digestibilities improved gradually by increasing the GR level. The energy digestibility was slightly improved in grass carp, while it was almost constant in tilapia. The percent gain, feed efficiency and protein efficiency ratio improved smoothly by increasing the GR level. However, the feed efficiency was still high (114% for grass carp and 119% for tilapia) even in the fish fed on a diet with raw corn meal. In tilapia, the daily feed consumption was not related to the GR. In the whole body composition, an increase of lipid content was observed with an increase of GR. A gradual increase in gelatinization thus improves gradually the nutritive value of corn meal for grass carp and tilapia. However, the effect is not so strong. Both species are good at utilizing corn meal, even in its raw form and at a high concentration, particularly tilapia.