BARIUM CARBONATE AS AN ALTERNATIVE INDICATOR TO CHROMIC OXIDE FOR USE IN DIGESTIBILITY EXPERIMENTS WITH RAINBOW-TROUT

Chromic oxide is suspected of violating the assumptions of an indicator of nutrient digestibility. In this study, four diets were fed to juvenile rainbow trout. Those diets contained either BaCO3 or BaCO3 plus Cr2O3 at levels of 0.5% or 1.0% of the dry diet as Ba and Cr. The diets incorporating Ba at 1.0% of the dry diet were not consumed by trout. Chromium was poorly recovered from diets (average of 13-14%) and a correction factor was used to determine apparent crude protein digestibility (ACPD). Recovery of barium from diets averaged 103-108%. There were no significant differences in ACPD using Ba or Cr at 0.5% of the dry diet. No apparent toxicological effects occured over a 24 day feeding period and histopathological evaluation of gastrointestinal tracts from fish fed 0.5% Ba revealed no lesions. Barium carbonate appears to be a suitable alternative to chromic oxide in digestibility studies with rainbow trout.