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 x 10(6) to 3.7 x 10(8) cfu g-1 and from 1.3 x 10(3) to 1.6 x 10(8) cfu g-1, respectively. Aeromonas spp. and Bacteroidaceae were predominant in four to five fish species. Of 206 strains examined, 65 (31.6%) produced > or = 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 (> or = 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.