The following experiments were carried out with the object of applying a new nitrofuran derivative nifurprazine (HB-115) for bacterial infectious diseases of yellowtail.
1 When young yellowtails were kept in the nifurprazine bath for ten minutes, the minimum safety concentrations were determined to be 13.3, 33.3 and 46.7 mcg/ml at water temperatures of 25, 20 and 15°C respectively, and mediam lethal concentrations 36, 96 and 238 mcg/ml, respectively.
2 Oral administrations of nifurprazine in feed to yellowtails at the rate 66.7 mg/kg BW per day for three consecutive days did not show any toxicity.
3 It was revealed by the bioautography using Staph. aureus as an idicator organism that nifurprazine which was administered orally at the rate of 66.7mg/kg BW per dar for three consecutive days was well absorbed.
4 The levels of nifurprazine in blood and various organs of yellowtails, which had been treated by medicated bathing was determined by the superposition method using E.coli as an indicator organlsm.
A positive correlation was observed between the nifurprazine levels and the temperatures.
Comparatively high concentrations were found in whole blood, plasma, skin and kidney, and low in muscle and gill. In liver, however, nifurprazine was not detected.
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