サケ科魚類の稚仔魚期における腸内細菌叢の形成時期について

日本水産学会

日本水産学会誌

Masu salmon Oncorhynchus masou and chum salmon O. keta were cultured from the stages of the fertilized egg to spring fry, and were used to know when the normal intestinal microflora was established. The microbial viable counts and the microflora of the egg surface, yolk sac, body surface, digestive tract, and intesinal contents of sac fry, advanced fry, and fingering were investigated. Simultaneously ambient water and their diets were also investigated microbiologically. The results obtained are summarized as follows. 1. The microbial viable counts on the surface of eggs were 10^3-10^6/g, and the microflora Flavobacterium/Cytophagaceae and Pseudomonas were dominant. 2. The yolk of alevin and sac fry were sterile, but from the body surface of sac fry 10^1-10^4/g viable microbial counts were obtained, the microflora were effected by the flora of ambient water, composed of Pseudomonas, Flavobacterium/Cytophagaceae, and Achromobacter. 3. The microbial viable counts in the whole digestive tract of sac fry and advanced fry were nil to 10^4/g, but the intestinal contents of advanced fry and fingering were 10^8-10^7/g. The microflora of the whole digestive tract of sac fry were effected by the flora of diet and ambient water, and were composed of Coryneforms and Pseudomonas. However, in later stages the microflora of the intestinal contents of advanced fry and fingering were mainly composed of Aeromonas as was the previous finding. 4. From the above results it was assumed that the normal intestinal microflora of salmonids were established when the yolk was absorbed and the digestive tract was activated, at the stage of advanced fry.

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