Microflora of Arctic charr, Salvelinus alpinus (L.): gastrointestinal microflora of free-living fish and effect of diet and salinity on intestinal microflora

Abstract. The adherent aerobic bacterial flora present in the gastrointestinal tract and faeces of free-living Arctic charr, Salvelinus alpinus (L.), from Lake Takvatn, Northern Norway, were identified both qualitatively and quantitatively. Approximately 10⁵ bacteria g⁻¹ were found in both the small and large intestines. The predominant bacterial species were identified as Aeromonas , Enterobacteriaceae, Micrococcus and Lactobacillus. Other microorganisms isolated included Acinetobacter, Cytophaga, Flavobacterium, Moraxella, Pseudomonas, Vibrio , Coryneforms and Streptococcus. The intestinal microflora of free-living fish was dominated by Aeromonas and Lactobacillus , but the intestinal bacterial flora of wild fish transferred to hatchery was affected by feeding them either a capelin roe diet or a commercial feed in fresh and sea water. Approximately 55% of the bacterial flora in intestinal contents from fish fed the capelin roe diet was Enterobacteriaceae when the fish were held in fresh and sea water. However, when the wild-caught charr were fed a commercial diet in fresh water, Aeromonas and Pseudomonas dominated in faeces, while Vibrio and Pseudomonas were predominant in the diet group held in sea water.