Acid-insoluble ash as an inert reference material for digestibility studies in tilapia, Oreochromis aureus

Ž . Acid-insoluble ash AIA was evaluated as an inert marker material for digestibility studies in Ž . tilapia. No significant differences were found in apparent digestibility coefficients ADC for nitrogen, dry matter or gross energy determined in a practical diet using naturally occurring AIA, Ž . or AIA supplemented with Celitee 0.5%, 1.0% of the diet , compared with values obtained using Ž . chromic oxide 0.5% . The use of supplementary Celite increased the accuracy of measurement of Ž . AIA in feed samples. Acid-washed sand 0.5% gave significantly lower ADC values than chromic oxide. As an alternative to using chromic oxide in ADC measurements, Celite supplemented AIA is inexpensive, easy to measure and gave comparable results in the present study with tilapia. q 2001 Elsevier Science B.V. All rights reserved.