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.
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.