Olive flounder, Paralichthys olivaceus is one of the most important cultured fish in Korea, its farming has been negatively impacted by viral, bacterial and parasitic diseases. Streptococcal infection was considered as a serious problem because of significant economic losses in olive flounder farm industry. The development and evaluation of vaccine for protection against infection by this agent were required. We evaluated the safety and efficacy of β-hemolytic Streptococcus (S.) iniae vaccine on olive flounder.

Efficacy of ciprofloxacin was evaluated in laboratory and field studies for control of streptococcal infection in flounder and eel. In disc diffussion test, all streptococcal strains showed high sensitivity to the ciprofloxacin. Minimum inhibitory concentrations of ciprofloxacin against all streptococcal strains used in this study were less than 0.195 μg/ml. In laboratory studies where fishes were challanged with Streptococcus iniae, significant reductions in mortality were observed among fish receiving ciprofloxacin (in feed) at 100 mg/kg/body weight or more daily for 3 d when compared with mortality of non-medicated controls.

The high mortality (65.5%) of young olive flounder (Paralichthys olivaceus) showing skin ulcers occurred in fish obtained from a commercial cultured farm at Donghae on the eastern coast of Korea at March 2006. The dorsal skin showed ulcer lesions and large amount of mucus. We isolated Ichthyobodo sp. from the gill, and Vibrio anguillarum from the liver and kidney of dead and diseased fish. All of the fish infected with the V. anguillarum and Ichthyobodo sp. were treated with 100 ppm formalin for 1 h, and treated with oxolinic acid for 4 h at 22℃, respectively.

Olive flounder (Paralichthys olivaceus) is the major mariculture fish in Korea. The annual aquaculture production of olive flounder in Korea during the period of 2003 was 300,000 ton (2002 Statistics, Ministry of Maritime Affairs and Fisheries, Korea Government). Anesthetics is very necessary in aquaculture to minimize stress and damage during harvesting, grading, transportation, spawning induction and handling to fish. In the present study, isoeugenol as new anesthetic in marine fish, especially olive flounder, was examined to know the efficacy and proper concentration. As a result, olive flounder adult was exhibited sedation at 5 ppm at 10 and 15℃, and 7.5 ppm at 20℃, respectively.

Neoheterobothrium hirame (N. hirame) is a large blood-feed gill-worm infecting the highly prized olive flounder. The present study was reported the occurrence and elimination of Neoheterobothrium infection from young cultured oliver founder in the western coast of Korea. Flounder (weight 18-25 g, length 10-15 cm) were obtained from a cultured farm at Taean of Korea at May 2006. A lot of flounder died with serious anemia. We isolated N. hirame from the buccal cavity wall of dead flounder. Adult parasites were 5-15 mm in total length, with 4 pairs of clamps on the pedunculated haptor and isthmus region embedded in host tissue, while immature and sub-adults were identified the attachment to the gill filaments, rakers and arches with the clamps.