Young yellowtails experimentally infected with Pasteruella piscicida were given single oral doses of florfenicol (FF, several strengths), ampicillin (ABPC), oxolinic acid (OA) or sodium nifurstyrenate (NFS-Na). The therapeutic effects of continuous administration of different doses of florfenicol mixed into pelleted feed and fish mince with and without binder were also evaluated. The first doses were given 3 hours postinfection and the fish were observed for 9 to 17 days after infection. The mortality rates were calculated on the basis of the number of fish which died during the experimental periods. Treatment with single dose administration gave mortality rates of 0, 0, 10, 70, 60 and 80 % for the 100, 50 and 25 mg/kg FF, 20 mg/kg ABPC, 30 mg/kg OA and 50 mg/kg NFS-Na treated groups, respectively, and 90 % in the non-medicated group. The therapeutic effects of the continuous administration of FF varied with the administration methods. The highest effect was obtained by mixing FF into pelleted feed. No deaths were observed in the groups given 6.3 mg/kg, or more of FF, and the ED50 was 0.82 mg/kg. On the other hand, the therapeutic effect of FF administered by mixing into fish mince without binder, was the lowest. The mortality rates of the 25 and 12.5 mg/kg FF treated groups were 20 and 40 %, respectively, and the ED50 was 10.5 mg/kg. Relatively good therapeatic effects were obtained by mixing FF into fish mince with binder. The mortality rates of the 50, 25, 12.5 and 6.3 mg/kg FF treated groups were 0, 10, 0 and 10 %, respectively, and the ED50 was considered to be lower than 6.3 mg/kg but higher than 0.82 mg/kg.
Three groups of young yellowtail naturally infected with Pasteurella piscicida were given florfenicol (FF) for 5 consecutive days at dosages of 0, 5, 10 or 30 mg/kg/day. Cumulative mortality varied but daily changes in mortality were similar among the groups before reatment. These differences of mortality before treatment do not seem so larges as to affect mortality rates during the dosing period and the evaluation of the treatment. Daily mortality decreased rapidly in the groups treated with 5, 10 and 30 mg/kg/day of FF, while it remained at a high level for a long time in the non-medicated group. Cumulative mortality of the FF-medicated groups during the dosing period (2nd day of dosing to 3 days after the last dosing) were significantly lower than those of the non-medicated groups. Among the medicated groups, the mortality of the 5 mg/kg/day FF-medicated groups were consistently higher than those of the 10 or 30 mg/kg/day groups. Cumulative mortality during the dosing period decreased with the increase of the FF dose. The mean cumulative mortalities were 23.1, 11.5, 8.3 and 6.7 % in the groups treated with 0, 5, 10 and 30 mg/kg/day of FF, respectively. From these results, it is concluded that 10 mg/kg/day of FF for 5 days is sufficiently effective as treatment for naturally occurring pseudotuberculosis in yellowtail.
IHN Virus titers in the fish bodies, rearing water and feces of artificially infected rainbow trout fry were investigated day after day. The fish were infected with immersion method by IHN virus Nagano isolate at the titer of 105.1 TCID50/ml for one hour. The fish began to die on 5 day post inoculation (PI) and final mortality was 97%. Virus was detected in fish body at first on one day PI and in every fish sampled after 3 day PI. High virus titers were maintained in fish after 4 day PI. Virus in rearing water was detected between 2 and 9 day PI and the highest titer (average) was recorded on 4 day PI at 103.8 TCID50/ml. Virus in feces was detected only in samples of 4 day PI but its titer were not high, therefore it was suggested that virus in feces did not affect strongly to virus titer in rearing water.
The egg, second, third, fourth and adult stages of Hysterothylacium haze (Nematoda : Anisakidae) obtained from Japanese common goby, Acanthogobius flavimanus, were described using light and scanning electron microscopy. The major dimensions and dimension indexes were given in association with body length and developmental stages. The dimensions were thought to be influenced by maturation and moulting. The characteristic features of each stage were also given.
Direct fluorescent antibody technique (FAT) was used in the detection of Flexibacter maritimus in experimentally infected black sea bream fry, Acanthopagrus schlegeli, by smear plus immersion. The sensitivity of the technique was compared with the conventional media culture method. Tissue sections of the skin, gill, liver and kidney were stained with fluorescent antibody. By culture method, tissues were separately homogenized, serially diluted and plate counted using Cytophaga agar in 100% seawater. Fluorescent antibody technique detected F. maritimus in all tissues from 15 min until all experimental fish died after 48 h. Whereas by culture method, the bacteria was detected in the skin only from 15 min to 3 h, in the gills from 1 h to 12 h, and in the internal organs from 15 min to 12 h but could not be detected thereafter because of the proliferation of other bacteria. Thus, FAT proved to be a more useful technique than the plate culture method in the diagnosis of induced Flexibacter infection in black sea bream fry.
Three halophilic Vibrio strains were isolated from diseased tilapia (Sarotherodon niloticus) cultured in the ponds located near by sea in Kagoshima Prefecture of Japan. The present isolates were identified as Vibrio vulnificus based on their morphological and biochemical characteristics; they were positive for fermentation of galactose, cellobiose, lactose and salicin, decarboxylation of lysine and ornithine, and growth at 42°C, while negative for arginine dihydrolase, V. P. reaction and sucrose fermentation. Two strains producing extracellular protease of high activity were resistant to human and tilapia sera, and pathogenic for tilapia and carp (Cyprinus carpio). One strain exhibiting low protease activity was also serum resistant and virulent for fish. A spontaneous mutant, which lost motility and decreased protease production, was non-pathogenic for fish.
Edwardsiella tarda, a well-known freshwater fish pathogen, has been recognized as an important pathogen of marine fish recently. Flounder (Paralichthys olivaceus) is one of such species. For elucidating the ecology of E. tarda in marine environment, the distribution of the bacterium in a flounder farm in Nagasaki city was examined in 1985 and 1986 by means of direct plating method on SS (Salmonella and Shigella) agar and enrichment culture method in DSSS (WYATT et al., 1979) and strontium chloride B (IVESON, 1971) medium. E. tarda was hardly detected from sea water or fouling materials on net cages except for during epizootic, but was isolated everytime from the intestines of 10 to 50% of apparently healthy flounder. During the epizootic the incidence of E. tarda in the intestines rose to 60 to 100% of the samples. When the numder of E. tarda in the intestines rose more than 103 CFU/g, the bacterium was also tend to isolate from the kidney. All of 13 selected isolates from environment and the intestines were found to be virulent to eel.
Phagocytosis of eel neutrophils isolated from peripheral blood was measured by chemiluminescence (CL) assay. When neutrophils were exposed to opsonized bacteria, CL response increased rapidly. CL response to the non-opsonized bacteria was much lower than that to the opsonized ones. The amount of CL response became larger in proportion to the concentration of normal eel sera as opsonin. The CL activity varied with the individual fish; neutrophils from three fish appeared to be similar in CL response, but those from a fish were weaker in the response. In this study, it was found that the CL assay could be applied not only to investigate the magnitude and kinetics of phagocyte but also to assess the serum opsonic activity.
Biological activities of eel complement activated through the alternative pathway, namely, chemotactic activity and leukocytosis-inducing activity, were investigated. The normal eel sera were mixed with zymosan or formalin-killed cells of selected bacteria (Escherichia coli, Edwardsiella tarda or Vibrio anguillarum) and incubated at 25°C for 60 min. The sera were separated from zymosan or bacterial cells by centrifugation. And then, this treated sera were heated at 50°C for 30 min. Chemotactic activity of the treated sera were determined by the modified Boyden chamber method. The distance of eel neutrophil migration toward the treated sera were significantly different from that toward the inactivated sera. The peripheral neutrophils increased in number rapidly 6-9 hr after the intraperitoneal injection with the treated sera. There appeared to be the leukocytosis-inducing activity in the treated sera. These biological activites of eel complement indicated in this study may play an important role in the non-specific defence mechanism of eel.
Prawns naturally infected with vibriosis collected from prawn farms and those experimentally infected with Vibrio sp. by placing them for 2h in bacterial suspension were studied histopathologically. No essential differences in histopathological findings were noted between the naturally and the experimentally infected prawns. Most characteristic pathological changes were extensive necrosis caused by severe bacterial invasion and multiple formation of melanized nodules in the lymphoid organ. Nodules were mostly composed of a bacterial colony in the center, a melanized zone around the bacterial colony and multiple layers of hemocytes encapsulating the melanized zone. Most of the hemocytes had pyknotic nuclei. No extensive necrotic lesions were found in other organs such as heart, gills, hepatopancreas, gonads, abdominal musculature, whereas small melanized nodules were frequently observed in these organs. The nodule formation is thought to be due to protective responses to invaded bacteria. It is conceivable that the lymphoid organ is highly susceptible to Vibrio sp. and in this organ successively invading bacteria overwhelm the protective responses, resulting in extensive necrosis which may possibly lead to the death of infected prawns.