Intestinal microflora of larval and juvenile stages in Japanese flounder(Paralichthys olivaceus).

Abstract

Investigations on the aerobic bacterial flora in the intestine of larval and juvenile stages in Japanese flounder (Paralichthys olivaceus) were carried out at two different fisheries stations. The bacterial flora of ambient water and feeds were also analyzed. The number of bacteria in the intestine of larvae measuring 10 mm in total length was 705 CFU/Fish, remained nearly constant until 14 mm, and decreased to 104 CFU/fish in 15-19 mm. The decrease in bacterial numbers was hypothesized to be due to the change in feeds from live diets (rotifer and brine shrimp) to artificial diets. The bacterial numbers on ZoBell''s 2216e agar were 104, 108, 105, and 106 CFU/ml or g in water, live feeds, artificial feed and minced fish, respectively. The composition of intestinal flora was characterized by two predominating groups of Vibrio and Pseudomonas followed by Moraxella, Cytophaga and Alcaligenes. Similar generic composition was recovered in water and live diets, while those of artificial diets comprised of Acinetobacter and Gram-positive bacteria in addition to Moraxella. Vibrio alginolyticus was frequently isolated from fish examined in one station where no apparent fish mortality occurred.