Recently an infection with a ciliate was found at a guppy (Poecilia reticulata) farm in Thailand. The clinical signs were scale loss and skin ulcer. The ciliate obtained from lesions of the diseased fish was identified as Tetrahymena corlissi based on the morphological characteristics. This is the first report of the disease in guppy caused by T. corlissi in Thailand. This paper describes some biological characteristics of T. corlissi isolates for the basis of treatment of the disease. The optimum temperature for the parasite reproduction was in the range of 25 to 35°C, but it multiplied slowly at 10 and 15°C. Multiplication was optimum in the pH range of 5.0-7.0, while, at pH 3.0 and pH 12.0, the parasite died within a few minutes. The guppies experienced high mortality at pH 4.0 and pH 11.0, while they did not die at pHs in the range of 5.0 to 9.0. The parasite survived in the PPYG medium when NaCl concentration was lower than 0.5%, but died in the medium when it was higher than 1.0%. All guppies survived for 12 h when exposed to 1.5% NaCl, for 6 h and 2 h when exposed to 2.0% and 2.5% NaCl, respectively. Whitish lesions appeared several days after the guppies were challenged with the parasite. All dying fish had many parasites in the lesions.
This paper describes the application of a modified ELISA, which offers a simple and semi-quantitative method to examine the attachment of P. damselae subsp. piscicida to CHSE-214 cells. The suitability of the ELISA procedure to assess this attachment was first confirmed by comparing the results of the ELISA with levels of attachment seen by microscopic examination. Significant differences were observed in the levels of adhesion to CHSE-214 among 32 P. damselae subsp. piscicida isolates from different species of fish and geographically different regions. Exposure of bacteria to low pH (pH 4-6) did not enhance their abilities to adhere to CHSE-214. However, treatment of two representative isolates, Italian I736 and Japanese SP92144, with seven different monosaccharides, revealed differences in their abilities to bind to the cells. Attachment of isolate SP92144 was significantly enhanced by treatment with both N-acetylneuraminic acid and L-fructose, while N-acetyl-D-galactosamine significantly decreased its ability to adhere. The attachment of strain 1736 increased significantly when treated with N-acetylneuraminic acid.
Since 1996, mass mortalities of cultured Japanese pearl oyster Pinctada fucata martensii have been occurring in the western Japan including the Uwa-Sea, Ehime Prefecture. Mortalities were accompanied with reddish-brown discoloration of the soft body, especially the adductor muscle of oysters. The condition of the disease was investigated through monitor of farmed and experimentally cultured pearl oysters and histopathological examinations of these samples in 1997-1999. The extent of reddish-brown discoloration of the adductor muscle was expressed as Δa-value using a colormeter. The discoloration started to occur from the southern area which experienced high temperatures in June, then extended to all the culture areas in August November. The mortalities occurred approximately one month after the appearance of the discoloration. As water temperature declined in October-November, the mortalities tended to decrease. These results indicate that the disease of pearl oysters is highly dependent on water temperature. Further, low temperatures in the previous winter appeared to suppress the occurrence of the disease in the following growing season, while high temperatures accelerated the occurrence and intensify the severity of the disease.
Sialic acid was identified and compared among 40 strains ofPhotobacterium damselaesubsp.piscicida (formerly, Pasteurella piscicida), isolated from a variety of fish species from geographically different regions. The isolates were divided into two main groups according to the molecular weight of their sialic acid. The first group comprised of 12 Japanese isolates, which contained sialic acid with a molecular weight of 22 kDa. The second group included 26 isolates from the Mediterranean region, which contained sialic acid with a molecular weight of 26 kDa. A subgroup of Group 2 (2 Mediterranean isolates) was also evident and had a sialic acid molecule of 38 kDa. TheP. damselaesubsp.damselaestrains (ATCC33539, ATCC35083 and NCIMB2184) had 26 kDa sialic acid molecules. Three isolates representing the three different groups ofP. damselaesubsp.piscicidawere treated withVibrio choleraeType III sialidase. Isolate OT97299 from Group 1 and isolate SA300695 from the subgroup were both susceptible to the sialidase, while isolate I736 from the main part of Group 2 was unaffected by the enzyme. All three isolates were susceptible to mild acid treatment.
In diseased Japanese pearl oyster Pinctada fucata martensii collected from Ehime, Japan from April to July 1998 where mass mortalities of cultured pearl oyster had occurred since 1996, histopathological features such as atrophy of the connective tissue in the mantle and adductor muscle were commonly observed. These histopathological changes were also reproduced in experimental pearl oyster by inoculation with hemolymph of diseased pearl oyster. Morphological changes of hemocytes in naturally and experimentally infected Japanese pearl oyster were examined. In naturally infected oyster, enlarged cells and the presence of granules and vacuoles in the cytoplasm of hemocytes were observed in hemolymph smear preparations stained with May Grunwald-Giemsa, and these changes were consistent with the histopathological changes. In experimentally infected oyster, these morphological changes of hemocytes were also correlated with the progression of histopathological changes. These results suggest that the observation of morphological changes of hemocytes in hemolymph smear preparations can be a rapid and convenient method for presumptive diagnosis of the disease occurring in Japanese pearl oyster.
The effects of high temperature on the parasitic stage (trophont) and encysted stage (tomont) ofCryptocaryon irritans were examined. The effects on trophonts were examined by rearing fish artificially infected withC. irritansat 25, 28, 31 or 34°C. The effects on tomonts were examined by incubating tomonts at the same temperatures. In these experiments, both the trophonts and tomonts showed normal developments below 31°C, whilst their development was badly damaged at 34°C. The effects of dissolved oxygen on tomont development were examined. Tomonts were incubated in hyperoxic (141%), oxic (100%), hypoxic (24%) and anoxic (0%) conditions. Under the hypoxic and hyperoxic conditions, tomont development was suppressed. Under the anoxic condition, tomonts died. However, when tomonts were transferred into an oxic condition after 2 or 4- week incubation in the hypoxic condition, development resumed, showing a rapid increase in theront excystment rates 10 to 11 days after the transfer. These results show a possibility that the supply of oxygen into water bottom along with the disappearance of thermoclines is involved in the autumn outbreaks of cryptocaryoniasis of cultured marine fish in floating net cages located in inner bays.
Southern flounderParalichthys lethostigmadistributed in the Atlantic waters of North America and Japanese flounderP. olivaceuswere challenged with the monogeneanNeoheterobothrium hirame, known so far as a parasite of Japanese flounder. Mature worms were obtained from the challenged flounders, both Japanese flounder and southern flounder, although the infection level was higher in the Japanese flounder. The result indicates that southern flounder as well as Japanese flounder can serve as the host ofN. hirame.
We evaluated hydrogen peroxide (H2O2) as an alternative anti-fungal agent of malachite green in the practical use at salmon hatcheries. Repeated exposure (2 times/week, just after fertilization to eyed-egg stage) to 1, 000 ppm of H2O2for 60 min showed efficacy comparable to malachite green for the inhibition of fungal infection in rainbow trout (Oncorhynchus mykiss) and brook charr (Salvelinus fontinalis) eggs. On the other hand, H2O2treated eggs from cherry salmon (O. masoumasou) and white-spotted charr (S. leucomaenis) showed a higher fungal infection rate and a lower eyed-egg rate than those of malachite green-treated eggs. The toxicity of H2O2to salmonid eggs varied with species, i.e. 1, 000 ppm of H2O2for 60 min was not toxic to eggs from brook charr and yamame salmon (land locked form of cherry salmon), but exposure to 750 ppm of H2O2appeared to be toxic to those from cherry salmon and white-spotted charr.
The Japanese Society of Fish Pathology held a symposium entitled “Current topics on protozoan and other parasitic diseases of fish in Japan” in Miyazaki on 27th September 2001. This symposium was aimed to have an overview of the current status of the researches on protozoan and other parasitic diseases of fish in Japan. Following a keynote presentation of the same subject in the world, two emerging diseases of marine fish in Japan, i.e. emaciation disease in tiger puffer and anemia in Japanese flounder, were introduced. Three species of myxosporeans are responsible for the former disease, and a monogenean Neoheterobothrium hirame causes the latter. The resent researches on kudoosis amami in yellowtail and amberjack, Heterobothrium infection in tiger puffer and blood fluke disease in yellowtail were also presented. The importance of the prevention against the fish protozoan and other parasitic diseases was discussed.