The reproductive emergence of Philometroides seriolae (ISHII, 1931) YAMAGUTI, 1935(nematode) from the yellowtail, Seriola quinqueradiata, was observed in a large exhibition tank of the Ohita Marine Palace from the middle of August to the beginning of September, 1969. From the observations the following process was suggested. A matured P. seriolae comes out from the interior of the fish body through a small hole made in the skin and hungs down from the hole for a few weeks or more by Ieavng one end of the body under the skin. The part of the worm body exposed to the outside loses elasticity and color and flattens. The end of the exposed part collapsed and thus the larvae are released. and scattered about widely owing to the swimming of the host. The number of the larvae carried by a mother worm varies with the size of the worms, being about 6 to 8 millions in worms measured over 30cm in length.
Outbreaks of scale protrusion disease in carp fishes are frequently observed at fish farms in Japan. Characteristics of a aeromonas isolated from all cases of diseased fish in freshwater were determined as well as ability of bacterium to produce experimental infection. The organism was Gram-negative rods. actively motile by means of a single polar flagellum, which showed some pleomorphism (Fig. 5, 6, 7). The bacilli occurred singly or in pairs and some had rounded ends. Catalase and oxidase, glucose fermented and gas produced, arginine dehydrolase produced (Table 3, 4, 5). On these findings the organism was identified as Aeromonas liquefaciens.
Some experiments were carried out to evaluate nifurprazine (HB-115) as a preventive agent for bacterial infectious diseases of fish. The results of those is as follows. 1. Nifurprazine is highly active against fish pathogenic bacteria, Vibrio anguillarum, Aeromonas sp., Chondrococcus columnaris or Vibrio sp. isolated from marine organisms. It was found that the antibacterial activity of nifurprazine was twenty to three hundred times as high as nitrofurazone furazolidone, chloramphenicol or chlortetracycline. It inhibited the growth of those bacteria at the concentrations as low as 0.01 to 0.04mcg/ml. 2. When eels were kept in the water containing nifurprazine at such a high level as 300 ppm for 30 minutes at 20°C, the treated eels did not show any toxic signs. 3. The results of experiments in which eels that had been previously infected with Vibrio anguillarum and Aeromonas sp. were treated by medicated bathing method with nifurprazine indicated that nifurprazine was highly effective in preventing eels from those bacterial infections. The preventive effect of nifurprazine is superior to those of the well known nitrofuran derivatives.
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.
An eel-farm company at Yaizu City imported a large number of elvers of the European Eel from France in the spring of 1969. Through the end of August into September eels grown to 15 to 20cm in body length died at a high mortality rate. Dying eels showed an abnormal swimming action suggestive of suffocation. Observations of eels showing such an action revealed that their gills were infected, without exception, with large numbers of Trichophrya (Fig.15), while it was rarely observed in healthy eels. As Trichophrya had never been reported in the Japanese Eel, this parasite was first suspected of being introduced from France. Afterwards a similar parasite, however, was discovered in high incidences in Japanese eels in ponds in a different district(Fig.6). This note is the first to describe the suctorian infection of the eel.
A huge number of elvers of the European Eel were imported, as seeds for culture, from France into Japan in the spring of 1969. From the end of March to the early part of May ichthyophthiriasis broke out among them in many ponds. The parasites occurred on the body and fins, but were never seen on the gills. The disease caused no mortality in any pond and disappeared late in May. Taking the fact into consideration that icthyophthiriasis has never been known to occur among the Japanese elvers, though the present authors found out afterwards one case of icthyophthiriasis amog large Japanese eels in a pond, the causative parasite was thought to have deen introduced, carried by the imported elvers, from France into Japan and to have multiplied explosively but temporarily.