Cultured black rockfish, Sebastes schlegeli, suffered mass mortalities during winter 2008 and spring 2009 in Korea, showing clinical signs of ulcer lesions and haemorrhages over their body surface. The aetiological agent was identified as Aeromonas salmonicida (strains RFAS-1, -2 and -3), which is a non-pigmented, slow-growing bacterium. Phenotypes of RFAS strains showed variation, while 16S rRNA, gyrB, rpoD, dnaJ and recA gene sequences of all the strains were affiliated to A. salmonicida. In particular, vapA gene sequences of the strains were most closely related to one of the five subspecies of A. salmonicida subsp. masoucida (=KCCM 40239(T) ). LD(50) values of RFAS-1 for intraperitoneal and intramuscular injection were 1.5 × 10(5.25) and 1.5 × 10(6.4) cfu/rockfish, respectively. However, A. salmonicida strains KCCM 40239(T) and SAS-1, which originate from masou and chum salmon, respectively, were not pathogenic to black rockfish. RFAS strains, possessing A-layer protein on their surface, exhibited β-haemolytic activity against rockfish erythrocytes and capability to survive in rockfish serum, which seem to be associated with virulence.

Turbot iridovirus (TBIV), a member of the genus Megalocytivirus in the family Iridoviridae, was isolated from diseased turbot, Psetta maximus (L.), in Korea in 2003. In this study, experimental infection of turbot, Japanese flounder, Paralichthys olivaceus (Temminck & Schlegel), and rock bream, Oplegnathus fasciatus (Temminck & Schlegel), with TBIV was performed to evaluate the viral susceptibility of these fish species. After virus exposure, the mortalities of turbot reared at 22 and 25 degrees C were 60% and 100%, respectively, suggesting that TBIV is the causative agent of the mass mortality of turbot that occurred in Korea in 2003. Moreover, TBIV was detected in Japanese flounder and rock bream by polymerase chain reaction after experimental infection (26 days post-inoculation) despite no viral pathogenicity in these fish, suggesting that these two fish species are also susceptible to the virus. It is possible that horizontal transmission of TBIV occurs among these three fish species because turbot is routinely cultured with Japanese flounder and rock bream in Korea.

Oxygen consumption rate of 8 to 12 mo old river puffer fish Takifugu obscurus was determined using a n automatic intermittent-flow-respirometer (AIFR). During the experiments, the fish were not fed and were kept in constant darkness and at constant temperature to avoid any extrinsic disturbances. It was clearly demonstrated that this species has a strong endogenous circadian rhythm in its instantaneous rates of oxygen consumption, although there were weak mlnor peaks of 11 4 to 11.7 h intervals. This endogenous rhythm appeared to be independent of the number of fish in the experimental chamber. The endogenous rhythm in the oxygen consumption rate observed in the present study may have profound implications for the physiological processes and biological rhythms of this species, and could also b e a good reference in determining the oxygen consumption rates of other aquatic organisms.

Effects of pentachlorophenol (PCP) on the oxygen consumption rate of the river puffer fish Takif ugu o bscurus 'Marine Biotechnology Lab., and 'Chemical Oceanography Division. Korea Ocean Research & Development Institute, Ansan. PO Box 29. Seoul 425-600. Korea ABSTRACT: Laboratory bioassays were conducted to determine the effects of pentachlorophenol (PCP) on the oxygen consumption of the river puffer fish Takifugu ohscnrus. Oxygen consu.mption of 6 to 9 mo old puffer fish was measured with an automatic intermittent-flow-respirometer (AIFR). Oxygen consumption rate was s~gnificantly increased by exposing fish to concentrations of 50, 100, 200 and 500 ppb PCP Follow~ng exposure to 50 or 100 ppb PCP, the instantaneous rate of oxygen consumption was considerably increased. T obscurus exposed to 200 ppb PCP, however, exhibited a breakdown in the biorhythm of oxygen consumption presumably due to a strong physiological stress caused by the higher PCP concentrations. River puffer fish exposed to 500 ppb PCP died in 10 h.