THE EFFECT OF CHROMIC OXIDE (CR2O3) ON AEROBIC BACTERIAL-POPULATIONS ASSOCIATED WITH THE INTESTINAL EPITHELIAL MUCOSA OF ARCTIC CHARR, SALVELINUS-ALPINUS (L)

Populations of aerobic heterotrophic bacteria present in the gastroint estinal tract of healthy Arctic charr, Salvelinus alpinus (L.), were e stimated using the dilution plate technique. The gastrointestinal bact erial flora of fish fed an unsupplemented diet was dominated by Gram-n egative bacteria of the genera Acinetobacter, Aeromonas, Agrobacterium , Alcaligenes, Cytophaga, Flavobacterium, Pseudomonas, and Vibrio, and Gram-positive bacteria of the genera Arthrobacter, Brevibacterium, Co rynebacterium, Kurthia, Lactobacillus, Microbacterium, Micrococcus, St aphylococcus, and Streptococcus. The composition of the indigenous aer obic bacterial flora in the digestive tract, and especially the microo rganisms isolated from the midgut and hindgut regions, was affected by inclusion of 1% chromic oxide (Cr2O3) in the diet. Many of the Gram-n egative bacterial genera and some of the Gram-positive bacterial gener a were not detectable in the Cr2O3-fed fish. The midgut and hindgut re gions in the Cr2O3-fed fish were dominated by Gram-positive microorgan isms of the genera Lactobacillus and Streptococcus. It is suggested th at the increased accumulation of Cr2O3 in the alimentary tract, as die tary compounds are removed, affects the attachment sites for the gastr ointestinal microflora or affects the gut epithelium directly.