Aerobic bacterial flora of eggs and larvae of milkfish, Chanos chanos, was investigated. Microflora in the incubating water of egg, rearing water of larvae, water source, and larval food was also analyzed. Aerobic bacterial flora of milkfish eggs was largely influenced by the bacterial flora in the incubating water. Both in eggs and in the incubating water Pseudomonas species were the dominant bacteria. During milkfish larval rearing, intestinal aerobic bacterial flora was examined at days 1, 3, 7, 10, 15, 18, and 21. Bacterial number in the larvae and rearing water significantly increased during the culture period up to day 18 but dropped significant at day 21. Pseudomonas species were detected from yolk-sac larvae (day 1) as the dominant bacteria, similarly to the normal flora in the rearing water. However, intestinal bacteria were predominated with Vibrio species when the yolk-sac was absorbed on day 3. Larval rearing water, water source, and larval food contained predominantly Pseudomonas species.
Two species of caligid copepods, Lepeophtheirus atypicus n. sp. and Caligus oviceps Shiino, 1952, are described based on the specimens obtained from moribund rabbit fish (Siganus fuscescens) cultured in a cage-net at the Penghus Hatchery Station on Pescadores Island, Taiwan. The new species bears close resemblance to L. goniistii Yamaguti, 1936, but can be easily distinguished from it by the armature on leg 3. The antennule, sternal furca, and leg 4 of these two species also exhibit difference. Lepeophtheirus species from rabbit fish in Japan reported as L. goniistii by Shiino (1952) is reidentified as L. atypicus n. sp. Caligus truncatogenitalis Roubal, 1981 is proposed to be relegated to the synonym of C. oviceps.
Immunogold technique in electron microscopy proved to be effective to demonstrate the virusantibody specificity using purified reference strains of infectious pancreatic necrosis virus (IPNV). Although some cross reactions were detected, it was possible to distinguish the major IPNV serotypes (Sp, Ab and WB) according to the different affinity for the antisera against the three reference strains which were binded to protein A-gold particles. Moreover, tubular structures with a diameter of 60 nm were detected presenting a high affinity for the gold particles, which suggests a viral origin.
Six marine birnaviruses isolated from turbot (Scophthalmus maximus) were compared with the infectious pancreatic necrosis virus reference strains Sp, Ab and WB from salmonid fish. This comparison was carried out by PAGE analysis of viral RNA and polypeptides and comparison of the reaction pattern with 4 monoclonal antibodies against the reference strains. High heterogeneity was found among the 6 isolates when comparing the RNA and polypeptide electrophoretic patterns and their reactions with the monoclonal antibodies. Most of the strains isolated from turbot could not be ascribed to any established serotype.
To study pathophysiological changes of sea-cultured coho salmon affected with erythrocytic inclusion body syndrome (EIBS), hemochemical assessments and lipid analyses were carried out using fish from one net-pen during an outbreak of EIBS. Fish examined were grouped by hematocrit (Ht) values which indicated the disease progression. Few differences in plasma components were observed in fish that were not seriously anemic. In fish with advanced disease (Ht value <20%), values of plasma total protein, total cholesterol, triglyceride and phospholipid were lower and potassium and GPT activity were higher. A decrease in plasma glucose and increases in plasma sodium, potassium and chlorine were observed in moribuned fish. Except for the moribund fish, blood thiobarbituric acid (TBA) values were higher than 20 nmol/ml in almost all of the fish and C22 : 6 level of liver phospholipids decreased as the disease progressed. It was considered that the changes in plasma constituent levels in the diseased fish reflected the effects of anemia.
A bacterial disease occurred in wild ayu Plecoglossus altivelis and pale chub Zacco platypus from July to November in 1993 in Gonokawa River, Hiroshima Prefecture, Japan. Two types of gliding bacteria were isolated from diseased ayu and pale chub showing ulceration or erosion of the body surface. Both types of bacteria formed yellowish colonies on modified Cytophaga agar within 14 days at 8°C. Based on their biochemical characteristics, one was identified as Cytophaga psychrophila and the other was classified as an unknown species of Cytophaga. These two Cytophaga species were also serologically differentiated from each other. The representative strains of both types were pathogenic to ayu and pale chub in challenge tests. As C. psychrophila was dominantly isolated, the species is considered as the main pathogen in this epizootic.
Mass mortalities of sevenband grouper Epinephelus septemfasciatus reared in Oita Prefecture were investigated. The outbreaks of the disease occurred in summer seasons (July to October; water temperature 25-28°C) of 1993 and 1994. Affected fish ranging 170 to 1, 850 g in body weight were characterized by upside down swimming and inflation of swimbladder. Histopathologically, necrosis and vacuolation in the central nervous tissues and retina were observed. Although bacteria or parasites associated with the disease were not detected from affected fish and no CPE was observed on RTG-2, BF-2, and EPC cell lines, spherical virus particles, 28 nm in diameter, were found abundantly in the cytoplasm of affected nerve cells of most of the affected fish. The virus was identified as a fish nodavirus (nervous necrosis virus), based on the results of fluorescent antibody technique test with anti-SJNNV rabbit serum and polymerase chain reaction test with primers for amplification of SJNNV coat protein gene. These results suggest that the mortalities of sevenband grouper were at least partly due to viral nervous necrosis (VNN). This is the first report describing VNN of sevenband grouper and the first case of VNN in the adult fish.