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 105 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 22l6e 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 composi tion 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.
The distribution of oxytetracycline (OTC) in male and female Macrobrachium rosenbergii was examined after the prawns had been given medicated feed containing OTC at levels of 2.5 and 5.0 g/kg of feed for 1 week and nonmedicated feed thereafter. OTC levels in the heads of both male and female prawns were consistently higher than in the muscles. Batches of both male and female prawns treated with higher dosages had significantly higher OTC residues in both head and muscle tissues than the batches treated with lower dosages. During treatment, peak concentrations in the head and muscle from each group were reached within 4-6 days. After drug treatment ceased, 13 days for the head and 10 days for the muscle were required to reduce OTC residues to safe levels in all batches of both sexes and dosages. In practice, to account for variations in water temperature, drug dosage, duration of therapy, and other environmental conditions, a withdrawal period of 21 days is recommended.
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