Studies on the Intestinal Microfiora of Salmonids. I, The Intestinal Microflora of Fish Reared in Fresh Water and Sea Water

摘要

Viable counts were determined seasonally on the intestinal contents of 22 masu salmon (Oncorhynchus masou) and 10 king salmon (Oncorhynchus tschawytscha) reared in fresh water and sea water, and on these ambient waters. Two kinds of media, fresh- and sea-water based media, were put in parallel. Over 1600 strains were isolated from the above samples. The composition of the microflora was determined according to the scheme of SHEWAN et. al. (1960). The results are summarized as follows: 1) The number of viable bacteria in both fresh and sea breeding waters was about 10^3 per milliliter with no observed seasonal variation. The composition of the microflora mainly included the genera Flavobacterium/Cytophaga, Achromobacter and Pseudomonas. 2) The number of viable bacteria in the intestinal contents of salmon ranged from 10^4 to 10^7 per gram. The intestinal microflora was comparatively simpler than that of the ambient water, and the floras of fresh- and sea-water reared salmon were quite different. The principal genera in the intestinal contents of fresh water reared salmon was genus Aeromonas and the family Enterobacteriaceae, while that of sea water reared salmon consisted mainly of the genus Vibrio.