Studies on the Intestinal Microflora of Salmonids—II Effects of Artificial Transplanting from Fresh Water into Sea Water on the Intestinal Microflora of Feeding and Non-Feeding Fish

Abstract

A total of 92 masu salmon (Oncorhynchus masou) which had developed silvering were divided into 4 groups. Three of these groups were transplanted from fresh water into sea water. The feeding conditions varied with the group. Viable counts were determined in the intestinal contents or slime of these salmon, in their ambient waters and in their diets. Over 1500 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) Microbial viable counts in the intestinal contents or slime of the fish which were transplanted under normal feeding conditions were nearly constant while those which were transplanted without being fed decreased rapidly. This decreasing tendency was found in both fresh and sea water reared non-feeding fish. 2) The predominant genus in the intestinal microflora of the fresh water fish was Aeromonas, while in sea water fish it was Vibrio. Upon transplanting the fish from fresh water into sea water, Aeromonas of the terrestrial type was gradually replaced by Pseudomonas as the proportion of sea water in the rearing water increased. This was followed by further replacement by Vibrio of the halophilic type which became predominant in the intestinal microflora. © 1976, The Japanese Society of Fisheries Science. All rights reserved.