The occurrences of Caligus sclerotinosus, a parasitic copepod on cultured red sea bream Pagrus major, were surveyed in fish farms and the phototaxis of adult caligid was experimentally examined. The parasite infection occurred from April to December, in which up to approximately 500 caligids infected the external surface of each diseased fish, covering the whole body surface, eyes and fins. The main disease signs were scale exfoliation, abrasion and ulcerative lesions on the body surface, and chipped fins. Listless swimming near the water surface was also observed. Daily mortalities were usually below 0.1%. When illuminated at different light intensities, most adult caligids showed positive phototaxis and those illuminated at 50 μmol/m2/s swam significantly faster than those illuminated at 200 and 800 μmol/m2/s. When infected fish were illuminated from one direction in a tank, 2.5% of caligids moved from fish to the illuminated wall of tank. When an infected fish and an uninfected fish were separated with a screen partition in each tank and illuminated from one side, 25% of caligids moved from fish in the shaded side to fish in the illuminated side, but never vice versa, showing that fish-to-fish transfer of C. sclerotinosus adults was affected by light conditions.
The virulence of Streptococcus iniae and Lactococcus garvieae strains was evaluated in farmed thread-sail filefish Stephanolepis cirrhifer by intraperitoneally injecting live bacterial cells. These two pathogens were highly pathogenic to thread-sail filefish. The efficacy of each commercial vaccine, namely, S. iniae vaccine, L. garvieae vaccine, and a combined vaccine of S. iniae and L. garviae was evaluated in the fish. The mortality was significantly lowered in both S. iniae- and L. garvieae-vaccinated groups compared to the control group, and both vaccines showed strong protection against the respective pathogens. Moreover, the combined vaccine showed strong protection against these two pathogens. These results suggest that these commercial vaccines are applicable in filefish aquaculture.
In 2008, the myxosporean emaciation disease was found in cultured Malabar grouper Epinephelus malabaricus in a fish farm in Okinawa Prefecture, Japan. The disease occurred in winter when water temperature ranged from 21 to 26°C, and the cumulative mortality reached 20-50% among culture tanks. In affected fish, cranial bones were externally apparent due to severe emaciation. The intestinal wall was very thin and the liver exhibited conspicuous green color. Morphological and molecular analyses demonstrated that the causative myxosporean was Enteromyxum leei. Histopathological examinations revealed that the epithelia of the intestine and bile duct of diseased fish were heavily infected with E. leei. The common bile duct was often obstructed by severe inflammation with degenerated tissues and bacteria, suggesting that the abnormal color of the liver was caused by cholestasis. Some diseased fish recovered in a laboratory when water temperature increased naturally to 27-30°C in summer months, and the parasite was not detected in those fish. Experimental transmission of E. leei to naïve Malabar grouper was successfully achieved by cohabitation with infected grouper or by feeding with the feces of infected fish. This is a new host and locality record for E. leei.
In this study, rainbow trout Oncorhynchus mykiss and amago salmon O. masou were used to study intra-ovum infection with Flavobacterium psychrophilum and Renibacterium salmoninarum, respectively. To investigate the possibility of intra-ovum infection of eggs in the coelomic cavity, the contamination of coelomic fluid and egg contents from ripe females were examined. The ranges of viable counts of F. psychrophilum and R. salmoninarum in coelomic fluid were 101.0-4.2 and 101.6-9.9 CFU/mL, respectively. However, neither F. psychrophilum nor R. salmoninarum was isolated from the egg contents. It was concluded that there was little possibility of intra-ovum infection of salmonid eggs in the coelomic cavity.
Lymphocystis disease virus (LCDV) causes a self-limiting disease in fish. However, recently, LCD outbreaks have increased, causing significant mortalities. In this study, we report the occurrence of two disease outbreaks in reared gilt-head sea bream Sparus aurata in the Tunisian coast. Presence of LCDV in diseased fish was confirmed by virus isolation using BF-2 cells and PCR amplification targeting the polymerase gene. Amino acid sequence analysis of the major capsid protein suggested that the LCDV strain was identical to nine strains previously isolated from the Mediterranean, Red Sea and South Atlantic coasts of Europe. These strains might have been disseminated through recent international trade.
An episode of mortality was observed in cultured ayu Plecoglossus altivelis with clinical signs including deep ulceration in the thoracic skin in affected fish in the Shiga Prefecture, Japan, in June, 2012. Bacteriological examination revealed that fish were infected with Flavobacterium psychrophilum, the etiologic agent of bacterial cold water disease (BCWD). Deep thoracic ulceration has not been reported in cases of BCWD in ayu. This lesion was successfully reproduced in ayu by slightly abrading the skin in the thoracic region prior to immersion challenge with F. psychrophilum. However, I could not determine the causative factor of the lesion in conventional fish farm management.