An ecological investigation on Edwardsiella tarda was carried out in two Japanese flounder (Paralichthys olivaceus) farms in Fukuyama City from April to December 1992. E. tarda was isolated from 86% of water, 44% of sediment and 14% of fish samples in one pond, and 22% of water, 0% of sediment and 2% of fish samples in the other pond, although epizootics caused by E. tarda were not observed in either pond. Serological studies proved that all the isolates of E. tarda from flounder and its environment shared a common heat stable O-antigen. Almost all the isolates tested exhibited pathogenicity to flounder by intramuscular injection. In survivability tests of selected isolates in sea water and freshwater, they perished within 7 days in sea water but survived longer period in freshwater. These results suggest that there is only one serotype of E. tarda which has pathogenicity to flounder in the environment of flounder farms.
Histopathological study was made on an epizootic of systemic mycosis due to Aphanomyces sp. in an ornamental fish species, dwarf gourami (Colisa lalia), imported from Singapore in 1991 and 1992. In almost all cases, the external clinical signs in infected fish included erosions and/or ulcers on the body surface, and swelling of the abdomen. Histopathological examination of the fish revealed that the disease was characterized by systemic granulomatous lesions associated with Aphanomyces sp. In this paper, we describe detailed histopathological features of the mycotic lesions and compared the features with those of other mycoses, such as mycotic granulomatosis, ulcerative mycosis, red spot disease and epizootic ulcerative syndorome. The present case shared similar histopathological features including mycotic granulomatous lesions, with those of earlier reported mycoses.
Hematological characteristics were compared between 10 triploid rainbow trout and 8 diploid ones. Hemocytes of the triploids were larger in size but smaller in number than those of the diploids, and no difference was found in hematocrit value between them. Blood hemoglobin concentration of the triploids was lower than that of the diploids. Mean corpuscular hemoglobin concentration (MCHC) of the triploids was the same as that of the diploids. Mean corpuscular volume (MCV) and mean corpuscular hemoglobin (MCH) of the triploids were higher than those of the diploids. According to these mean corpuscular constants, the blood condition of the triploinds was classified as macrocytic anemia. It was concluded that macrocytic anemia of the triolid rainbow trout was due to the increased genome number which increased in proportion to ploidy.
Triploid rainbow trout were compared with diploid ones in oxygen consumption, hypoxic tolerance, and mortality from bacterial gill disease. Triploids showed almost the same rate of oxygen consumption (ROC) with diploids at environmental dissolved oxygen concentration between 2-6ml/l, but the ROC of the triploids was significantly lower than that of diploids at 1.6ml/l. Triploids also showed a surfacing behavior at higher dissolved oxygen concentrations than diploids. However, there was only a minor, if any, difference in dissolved oxygen concentration at which fish began to lose equilibrium. Triploids which had lost equilibrium needed longer time for recovery. Triploids showed higher mortalities in water under 50% saturation of dissolved oxygen when infected with bacteral gill disease. It was thought that the poor intake of oxygen due to bacterial gill disease produced more serious hypoxia in triploid rainbow trout.
Two species of parasitic copepods are described based on the materials obtained from the pondcultured black sea bream (Acanthopagrus schlegeli) in Tainan County, Taiwan. They are : Caligus acanthopagri n. sp. found on the host's body surface and Caligus multispinosus on the host's gills and in the gill cavities. The new species is very close to Caligus latigenitalis but can be distinguished from it by the fine structures on the exopod of leg 4. This study shows that Caligus dieuzeidei reported by Shiino in 1954 from Sparus macrocephalus (=Acanthopagrus schlegeli) was a misidentification for C. latigenitalis.
Sudden outbreak of a disease caused by the blood fluke Paradentacylix occurred in May, 1993 among net-cage cultured juvenile amberjack, Seriola dumerili which had been imported from Hainan, China, a few months before the onset of the disease. The cumulative mortality rate ranged from 50 to more than 80% in one month. Dead fish were characterized by opened mouth and opercula, showing typical sign of suffocation. Parasitological examination revealed that eggs of P. grandispinus and/or P. kampachi were accumulated in the afferent arteries of the gills of all dead fish. Since no other pathogens were detected, it was concluded that the mass mortality was caused by these blood flukes. It could not be specified whether the cercarial invasion had occurred prior to or after the introduction of the fish into the Japanese waters.
On the basis of the 16S rRNA sequence data analysis among the closely related species, the specific primers for Cytophaga psychrophila were constructed. The specificity in amplifying the 16S rRNA of C. psychrophila was confirmed by using some selected strains of the related species. In addition, it was revealed that these specific primers distinguished C. psychrophila from other principal fish pathogens. The present PCR technique is expected to be a powerful tool for the diagnosis of cold-water disease.