Preventive and therapeutic effects of oxolinic acid (OA) against the vibrio disease of cultured rainbow trout were examined. The experiment was carried out in two culture ponds (A and B) in Shizuoka prefecture from September to December in 1973. The fish in pond A (1370 fish, 50kg total body weigh) were administered OA (2.5mg/kg) in the diet once a day for 3 months. The fish in pond B (1370 fish, 50kg total body weight) were fed the normal diet for the first 9 days, and then the fish were administered OA (20mg/kg) on 10th day, 10 mg/kg on 11th and 12th days in the diet. The number of dead fish was 14 in pond A after 3 months, and the number of dead fish in pond B steadily increased until several days after the start of medication, whereafter the death rate leveled off. Causative organisms were isolated from the liver and digestive tract of the infected fish in pond B. One of organisms was identified as a genus Vibrio, and the sensitivities of this organism to teracycline, chloramphenicol and OA were 0.19, 0.19 and 0.01mcg/ml, respectively, in terms of MIC. No behavioral and histological abnormalities were found in the alive fish either from pond A or B after 3 months.
A new species of acanthocephalan, Pseudorhadinorhynchus samegaiensis (Echinorhynchidea, Illosentidae), was found from the intestine of 2 years old rainbow trout cultured at Samegai Trout Experimental Station, Shiga Prefecture, in May, 1974. Sixty-seven males and 101 females were collected from 29 of 35 fishes examined. Acanthocephalans were fixed in 70% ethanol under pressure, stained with Heidenhain's hematoxylin and mounted in balsam. Type specimens are deposited in the collection of the National Science Museum, Tokyo.