Production of amylase by the intestinal microflora in cultured freshwater fish

The amylase‐producing ability of the intestinal microflora in cultured specimens of ayu, carp, channel catfish, Japanese eel and tilapia was determined. Mean viable counts of aerobes and anaerobes ranged from 1·1×106 to 3·7×108 cfu g−1 and from 1·3×103 to 1·6×108 cfu g−1, respectively. Aeromonas spp. and Bacteroidaceae were predominant in four to five fish species. Of 206 strains examined, 65 (31·6%) produced ≥0·01 U amylase ml−1. The percentage of producers differed among families and genera of bacteria and fish species. While 56% of the anaerobes produced amylase, only 20% of the aerobes did. More than 50% of Aeromonas, Bacteroidaceae and Clostridium strains produced amylase efficiently while Acinetobacter, coryneforms, Enterobacteriaceae, Moraxella, Plesiomonas and Streptococcus strains did not. High amylase production (≥0·05 U ml−1) was found in 12 strains, 11 from Aeromonas and one Pseudomonas. The percentage of high amylase producers in Japanese eel was lower than the other four fish (2–30%). These results strongly suggest that the amylase produced by the intestinal microflora play an important role in the digestion of starch in freshwater fish to some extent.