A new species of turbellarian, provisionally placed in the genus Paravortex (Graffillidae, Rhabdocoela) is a parasite of marine tropical fishes and has become a conspicuous problem in saltwater aquaria. The worm infects fishes in several families and is most often seen on the yellow tang Zebrasoma flavescens, which is the principal host in this study. Worms increase in length and then leave the host. Off-host worms continue to grow and as many as 160 young develop within them. Ciliated young discharged from a rupture in the body wall of the adult quickly reinfect available hosts, and this alternate on and off-host pattern results in a periodicity of infections. The life cycle requires about 10 days at 24.5°C, with infections of as many as 4500 worms per fish after three generations. Heavily infected fish, with worms concentrated on the body, develop an acute focal dermatitis with an associated Vibrio infection. A formalin bath was effective in eradicating the parasite, but neon gobies (Gobiosoma oceanops) were ineffective as cleaner fish and they became infected as well.
Five month feeding experiments were conducted on the carp, Cyprinus carpio, with diets which included oxidized methyl linolate of unsaturated fatty acid. The experimental diets included 10% of 30, 40, 90 and 200hrs-oxidized methyl linolate and 0 or 50mgα-tocopherol acetate per 100g diet. The diets for control included 10% purified soy bean oil and 0 or 25mg α-tocopherol acetate per 100g diet. Carps fed the tocopherol free diets including oxidized methyl linolate showed less growth and visibly thinner across the back. The histopathological signs were characterized by atrophy and necrosis of white muscle fibers and visceral ceroidosis. Carps fed a diet containing 40hrs oxidized methyl linolate with 50mg α-tocopherol acetate and a tocopherol free diet including soy bean oil showed lesser growth, visceral ceroidosis and no sign of myopathy. No pathological change was found in carps fed the diet including soy bean oil supplemented with 25mg α-tocopherol acetate. These results indicated nutritional myopathy of the carp was caused by oxidized fatty acid and tocopherol deficiency.
Five hundred and sixty blue rockfish (Sebastes mystinus) from central California were found to have no larval anisakid nematodes. The diet and presence of larval anisakids in S. mystinus are compared to five other species of rockfishes form the same kelp forest. Sebastes mystinus was successfully infected with larval anisakids in laboratory experiments. It is suggested that host diet plays an important role in limiting natural infections.
A fillet from a blue rockfish (Sebastes mystinus) had large, dark solid nodules simular to those occasionally reported from other specimens of Sebastes spp. by local anglers. These nodules contained an acid-fast bacterium similar to Mycobacterium sp. The nodules decrease the food value of the fish and may indicate a potential human health hazard.
Descriptions are given of two new species of Gyrodactylus collected from the body surface of eel, Anguilla japonica, in greenhouse ponds at Yoshida, Shizuoka Pref. G. egusai sp. nov. differs from most simuilar G. varicorhini ERGENS et IBRAGIMOV, 1976 in considerably smaller hamuli and marginal hook proper. G. joi sp. nov. is distinguished from most related G. anudarini ERGENS et DULMAA, 1968 in the shape of the marginal hook proper. Long term changes in the occurrence of Gyrodactylus nipponensis on the gill fillaments and G. egusai and G. joi on the body surface were studied during 1980-1985. Gyrodactylus on the body surface was more frequently found than G. nipponensis throughout the study period. Gyrodactylids on both sites were less frequently observed in 1983-1985 than in 1980-1982, and also in summer than in the other seasons. Possible reasons for the seasonal and yearly fluctuations in Gyrodactylus populations are briefly discussed.
Tilapia, Tilapia mosambica, were experimentally infected by intramuscular injection with 108 CFU/ml of Edwardsiella tarda (J3N strain) isolated from diseased tilapia, and examined on 24, 48, 96 and 120 hours after injection. Fish 24 and 48 hours after the injection showed swollen and erosious lesions and muscular necrosis with bacterial multiplication and inflammatory calls at the injected areas, and focal necrosis with bacteria-laden inflammatory cells in the liver, spleen, kidney and heart. Fish 96 and 120 hours after injection were moribund showing swollen and ulcered lesions at the injected areas, small white nodules in the liver and spleen. The injected lesions showed muscular necrosis with bacterial multiplication and inflammatory cells. The liver, spleen and hematopoietic tissue showed focal accumulation of macrophages and production of granulomas in the infected lesions. The heart showed focal necrosis with bacterial multiplication and inflammatory cells. Gills showed bacterial embolism in lamellae. These histopathological signs of experimentally infected tilapia resembled to those of naturally infected fish.
Studies were made on the histopathology of tiger puffer inoculated with tissue extracts or viral cultures from fish naturally infected with Kuchijiro-sho. All the inoculated fish showed pathognomonic symptom of Kuchijiro-sho and the histopathological changes were the same as those in the fish naturally infected with the disease.
A light and electron microscopic study was made on yellowtail fingerlings with ascites obtained from a fish farm in Shizuoka Prefecture in June, 1984. The most characteristic symptom of the disease was abdominal ventral distention caused by accumulation of low viscous and light yellow transparent filuid. General gross findings were redness of the liver and pallor of the gills. Histopathological examination revealed hepatic partial necrosis with congestion as well as severe pancreatic necrosis, which occurred earlier than the hepatic lesions, and partial edematous changes in both submucosa of the stomach and ellipsoids of the spleen. The kidney showed vacuolar degeneration of renal tubules. In addition, slight catarrh was seen in the pyloric caeca and intestine. On examination under the electron microscope, degenerated hepatocytes showed vesiculation of rough endoplasmic reticulum or vacuolation of mitochondria. Hexagonal or round virus particles measuring 62.2-68.9 nm in diameter without envelope were found in the cytoplsm of degenerated hepatocytes. These particles were gathered in vaculoles or scattered in the whole cytoplasm but never seen in the nucleus. Almost all pancreatic acinar cells showed decrease of zymogen granules and vesiculation of rough endoplasmic reticulum. A few virus-like particles measuring 58.8-64.7 nm in diameter were found in a small cytoplasmic vacuole of degenerated pancreatic acinar cells.
A histopathological study was made on yellowtail fingerlings with ascites obtained from a hatchery in Kagawa Prefecture in June, 1983 and those inoculated with YAV isolated form them. The inoculation experiment was done in June, 1985. Living inoculated fish were sampled at random daily after inoculation. The most characteristic pathological changes observed in naturally infected fish were extensive pancreatic acinar cell necrosis, hepatic parenchymal cell necrosis, and hepatic hemorrhage. Kidney tubule cell necrosis, gastric edema and desquamative catarrh of the pyrolic caeca and intestine were observed in part of the fish studied. No pathological change was observed in any organ of all the inoculated fish examined 1 to 3 days after inoculation. Minor necrotic lesion was observed in the pancreas of 1 of the 4 fish sampled 4 days fater inoculation. Extensive pancreatic necrosis and hepatic necrosis and hemorrhage similar to those observed in naturally infected fish were observed in all the inoculated fish 5 days after inoculation. Kidney tubule cell necrosis was barely observed only in half of the fish. In 3 of the 11 fish sampled 6 to 10 days after inoculation necrosis was observed both in the pancreas and in the liver, but in 4 of the 11 fish extensive lesions were observed only in the pancreas. Moreover regeneration of pancreatic tissue was observed in extensive lesions in fish sampled 8 and 10 days after inoculation. No distinct pathological change was observed in any organ in the remaining 4 fish. The observations of naturally and experimentally infected fish strongly suggested that acinous tissue of the pancreas and parenchymal tissue of the liver were primary tissues involved in fingerling yellowtail YAV infection. Moreover the observations of experimentally infected fish suggested that necrosis occurred earlier and progressed more rapidly in the pancreas than in the liver and that the fish in which the pancreas was extensively infected but the liver remained uninfected could survive. The kidney, stomach, pyloric caeca and intestine were involved in most severely infected fish.
Viral ascites occurred among fry of yellowtail, Seriola quinqueradiata (3-15 cm in body length) reared in some bays of Mie Prefecture in 1984 and 1985. The serious cases of diseased fish were histopathologically observed in this study. They showed the expanded abdomen and lay on the botoms of net cages, resulting in big mortalities. Internal signs were characterized by accumulation of red or yellow-colored ascitic fluid and catarrhal intestine. Hemorrhage occurred in the liver, stomach and pyloric regions. Pale-coloration was also found in the kideney, spleen and gills. Livers of all fish displayed focal and diffuse necrosis of hepatic cells, followed by congestion and hemorrhage. Pancreatic cells of all cases were necrotized, accompanying with no sign of inclusion bodies. Intestines usually showed desquamative catarrh without invasions of bacteria. Kidneys of most cases showed degeneration and necrosis of renal epithelia and slight necrosis of the hematopoietic tissue. Spleens also showed necrosis of pulps and sheathed arteries. Stomachs of most cases displayed hemorrhage and edema in the submucosa.