Investigations on the aerobic bacterial flora in the intestine of larval and juvenile stages of rockfish Sebastes schlegeli, tiger puffer Takifugu rubripes and red grouper Epinephelus akaara were carried out in relation to the microflora of ambient waters and feeds.
The numbers of bacteria on ZoBell's 2216e agar in the intestine of rockfish (6-18mm in total length), tiger puffer (4-21mm) and red grouper (5-15mm) ranged from 6.0×10³ to 3.1×10⁶, 8.6×10⁴ to 2.4×10⁶, and 1.4×10³ to 2.6×10⁵ CFU/fish, respectively. A distinct decrease in the bacterial numbers was observed in a group of rockfish when their feeds were changed from live diets (rotifer, brine shrimp and/or copepods) to artificial diet and minced fish. The level of bacterial counts were 10⁴, 10⁷-10⁸, 10⁵, 10⁴ CFU/ml or g respectively in water, live diets, minced fish and artificial diet.
The intestinal microflora of rockfish and tiger puffer was characterized by predominating groups of Vibrio, Acinetobacter and Pseudomonas, while that of red grouper was comprised almost exclusively of Vibrio. However, the incidence of vibrios was much reduced in the group of rockfish which were fed rotifers medicated with sodium nifurstyrenate. The bacterial composition in the intestine of these fishes was found influenced by the microflora of foods ingested rather than ambient water.