Infectious hematopoietic necrosis (IHN) is generally believed to be a virus disease of very young salmonids. In recent years there have been increasing numbers of unpublished reports that this disease has been occurring uncharacteristically in fish as old as 7-14 months. Sockeye salmon (Oncorhynchus nerka) of this age the histological changes were not severe. Intestinal tract granular cells thought to be pathognomic in young fish were conspicuously absent. Kidney imprints showed necrobiotic bodies however, and subtle changes were observed in the spleen and kidney hematopoietic tissue.
The present study was designed to investigate the pharmaco-dynamic properties of trimethoprim (TMP) in ayu, Plecoglossus altivelis, after oral administration of TMP-sulfadoxine (SDX) mixture for the control of vibriosis. The results obtained are summarized as follows: 1. Following a single administration of 30 mg of TMP-SDX (1:5) mixture per kg body weight, the highest tissue levels of TMP were obtained 2 hours after medication in the liver at the level of 10.8 mcg/g, 6 hours in the kidney at the level of 4.4 mcg/g, 2-3 hours in the muscle at the level of 1.8 mcg/g, and 1 hour in the blood at the level of 0.4 mcg/ml. 2. Following daily administration of 30 mg of TMP-SDX (1:5) mixture per kg body weight per day for 10 days, TMP level became undetectably low 24 hours after the last medication in the liver, 48 hours in the kidney and the muscle, and 6 hours in the spleen and the blood. 3. It is concluded that TMP is once retained in the tissue for some hours, and is excreted almost completely from the fish body within a day. Therefore, it is necessary to administer TMP-SDX mixture to ayu more than once a day to maintain constant tissue levels of TMP in ayu.
Seventeen cultures of Enteric Redmouth Bacterium were examined biochemically at selected temperatures. Incubation temperature altered the motility of the bacterium. At 9°C nonfunctional peritrichous flagella were produced, while at 18, 22, and 27°C the bacterium was motile. The cells were nonmotile at 37°C due to a lack of flagellar production. The percent guanine plus cytosine was determined to be 47.95±0.45 (P=0.05). This work supports the proposal of Yersinia ruckeri as the genus and species designation of the Entric Redmouth Bacterium.
The pharmacokinetic and toxicological examinations of piromidic acid (PA, 8-ethyl-5, 8-dihydro-5-oxo-2-pyrrolidinopyrido[2, 3-d]pyrimidine-6-carboxylic acid) were studied in ayu Plecoglossus altivelis, amago salmon Oncorhynchus rhodurus and eels Anguilla japonica and A. anguilla orally administered a single or multiple dose(s) of PA with the following results. 1. The absorption, distribution and excretion data obtained from the bioassay revealed that orally administered PA was easily absorbed and quickly became distributed in blood and major organs. Peak levels were reached in 3 h (in ayu) or 6-24 h (in amago salmon) after the administration of PA, followed by a gradual decrease. The levels of PA in liver and kidney were higher than in blood and plasma. 2. In acute toxicity study, the LD50 value for ayu was more than 2, 000 mg/kg. The subacute toxicity of PA was studied in ayu (80 mg/kg), amago salmon (800 mg/kg) and eels (400 mg/kg) administered PA once daily for 5-10 days. Except for accidental death of two eels, all fishes receiving PA survived without any clinical and histopathological changes. 3. Disappearance of PA from the tissues in amago salmon was studied after the administration of 40 mg/kg of PA for 7 consecutive days. Peak levels of PA in the tissues tested attained within 6-12 h following administration. A level below the assay limits (0.25-0.56 μg/ml or g) was reached 96 h post dosing. No evidence of long term residue was found in any of the tissues tested.
The efficacy of piromidic acid (PA) against various bacterial diseases in cultured fish was evaluated clinically. PA was used for the treatment of furunculosis in Amago (Oncorhynchus rhodurus), Yamane (O. masou) and brook trout (Salvelinus fontinalis), vibriosis in rainbow trout (Salmo gairdneri), êdwardsiellosis and red disease in eels (Anguilla japonica). PA was mixed in feed and consecutively administered for 5-11 days at the rate of 10, 20 and 40 mg/kg. The fish in every disease responded to PA with reduction in mortality and were found to be cured of the disease during medication or within a few days post dosing. The efficacy of PA against furunculosis was more remarkable than those of sulfisozole and sulfamonomethoxine (100-200 mg/kg/day). When PA was administered to Amago with furunculosis at 10 mg/kg for 5 days, mean blood levels in diseased fish were found to be 0.81, 1.50 and 1.39μg/ml 3 hours post dosing on 1st, 3rd and 5th day of the medication, respectively. It was revealed that PA was well absorbed in the diseased fish without a marked difference in its absorption among them. The administration of PA caused no abnormality in 120, 000 fish of salmonids and 320, 000 fish of eels including elvers. The results obtained from this study suggest that PA can be used for the control of bacterial diseases in salmonids and eels.