바이오플락 양식기술 적용 넙치, Paralichthys olivaceus 수용밀도에 따른 수질변화 및 혈액학적 성상 변화

The Paralichthys olivaceus (mean weight 34.3±3.5 g) was used in the conduction of density experiment in this study to establish the optimal density determination for a period of 13 weeks. The density consisted of four groups. These were group 1 (500 fish, 40 fish m-2), group 2 (750 fish, 60 fish m-2), group 3 (1,000 fish, 80 fish m-2) and group 4 (1,250 fish, 100 fish m-2), each in 12.56 m2 circular water tanks. In the high density groups, such as groups 1 and 2, the nitrite was increased to over 21 mg L-1 (group 3) and 25 mg L-1 (group 4). The experiment of the groups was terminated by skin ulcers and mortality after 49 days for group 3 and 43 days for group 4. The water quality environment, such as the water temperature, dissolved oxygen, salinity and pH, remained constant. The ammonia and nitrite in groups 1 and 2 remained stable after ammonia and nitrite peak. However, the experiments in groups 3 and 4 were terminated due to the mortality induced by high nitrite. Hematological parameters, such as hemoglobin and hematocrit, were significantly decreased in the high density groups. The plasma components were significantly changed in the high density groups, such as groups 3 and 4. The mean weight of groups 1 and 2 after 13 weeks were 91.3 g and 83.7 g, respectively. The survival rates were 99.4% and 98.2%, respectively. The final FCR was 0.6 in both groups. The results of this study show that the density of 80 fish m-2 or more induce mortality due to high nitrite with hematological changes. Additionally, they indicate that the 60 fish m-2 indicate proper density in bio-floc environment in olive flounder weighing less than 100 g.