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 gastrointestinal tract of healthy Arctic charr, Salvelinus alpinus (L.), were estimated using the dilution plate technique. The gastrointestinal bacterial flora of fish fed an unsupplemented diet was dominated by Gram-negative bacteria of the genera Acinetobacter, Aeromonas, Agrobacterium, Alcaligenes, Cytophaga, Flavobacterium, Pseudomonas, and Vibrio, and Gram-positive bacteria of the genera Arthrobacter, Brevibacterium, Corynebacterium, Kurthia, Lactobacillus, Microbacterium, Micrococcus, Staphylococcus, and Streptococcus. The composition of the indigenous aerobic bacterial flora in the digestive tract, and especially the microorganisms isolated from the midgut and hindgut regions, was affected by inclusion of 1% chromic oxide (Cr2O3) in the diet. Many of the Gram-negative bacterial genera and some of the Gram-positive bacterial genera were not detectable in the Cr2O3-fed fish. The midgut and hindgut regions in the Cr2O3-fed fish were dominated by Gram-positive microorganisms of the genera Lactobacillus and Streptococcus. It is suggested that the increased accumulation of Cr2O3 in the alimentary tract, as dietary compounds are removed, affects the attachment sites for the gastrointestinal microflora or affects the gut epithelium directly.