ESTIMATION OF APPARENT DIGESTIBILITY COEFFICIENTS IN RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) USING DIFFERENT MARKERS - 1 - VALIDATION OF MICROTRACER F-NI AS A MARKER

Microtracer F-Ni was evaluated as an external marker in digestibility studies with rainbow trout feed. The average particle weight was 15.9 +/- 2.1 mu g weight (mean +/- SD, it n = 9) and average diameter was 2 33.4 +/- 73.6 mu m (n = 20). At an inclusion level of 1% (as is basis) , the concentration of microtracer analysed from digesta and faeces sa mpled, appeared to increase sequentially as it moves down the digestiv e tract. At other levels of inclusion, there were variations in marker concentrations estimated in the various sections of the gut, Apparent digestibility coefficients (ADC) for protein and dry matter were comp ared for different faecal collection procedures, collection intervals and using Microtracer F-Ni, chromic oxide and acid insoluble ash as ma rkers. The ADC values generated by using microtracer F-Ni were consist ent and in close agreement with the ADC values calculated using chromi c oxide as a marker in all combinations of intervals and collection pr ocedures. The ADC values determined using acid insoluble ash (AIA) as a marker were inconsistent and higher than the ADC values calculated u sing either chromic oxide or microtracer F-Wi markers. Microtracer F-N i incorporated at 1% holds promise as an external marker in feed diges tibility studies with rainbow trout. (C) 1998 Elsevier Science B.V. Al l rights reserved.