Juvenile Paralichthys olivaceus (mean length 19.8±2.6 cm, mean weight 97.8±15.8 g) were exposed for 96 hours to different nitrate concentrations of 0, 62.5, 125, 250, 500, 1,000, and 1,500 mg L-1 in biofloc and 0, 62.5, 125, 250, 500, and 1,000 mg L-1 in seawater. Median lethal concentration values (LC50, the concentration at which 50% of mortality occurred after 96 hours of exposure) of nitrate to P. olivaceus in biofloc and seawater were 1,226 and 597 mg NO3 L-1 (P<0.05), respectively, revealing a higher toxicity of nitrate to P. olivaceus in seawater than in biofloc. In hematological parameters, hematocrit level in P. olivaceus exposed to nitrate was significantly increased only at a concentration of 1,000 mg L-1 in biofloc and at concentrations higher than 250 mg L-1 in seawater, but no significant changes in hemoglobin were found in biofloc and seawater. In plasma parameters, aspartate aminotransferase (AST) and alanine aminotransminase (ALT) were significantly increased by nitrate exposure in biofloc and seawater, but no significant changes in alkaline phosphatase (ALP) were found in biofloc and seawater. Results of this study indicate that nitrate exposure to P. olivaceus have a lethal toxic effect and alter hematological and plasma constituents of flatfish P. olivaceus. Given relatively lower toxicity of nitrate in biofloc than in seawater, the use of biofloc in aquaculture may reduce potential toxic effect caused by nitrate in feces and feed residue.

급격한 수온의 변화는 어류의 생리학적인 측면에서 스트레스를 유발한다. 본 연구에서는 넙치 (Paralichthys olivaceus)로부터 각 수온별(9, 12, 15, 18 및 21℃) 조건에 따라 24 및 48시간 동 안 노출시킨 후에, 혈액생리학적 분석, 스트레스 단백질로 알려진 Hsp70 mRNA 발현 및 산소 소비량을 조사하였다. 혈액학적 분석에서 hematocrit (Ht) 및 hemoglobin (Hb), 혈장 코티졸 및 글루코스의 변화, aspartate aminotransferase (AST) 및 alanine aminotransferase (ALT), NH3, 삼 투질농도(osmolality) 및 총단백질(total protein, TP)은 9℃ 및 12℃에서 다른 수온별 실험구에 비 해 대부분의 항목에서 유의적인 차이를 보였다. Hsp70 mRNA 발현은 9℃ 및 12℃에서 다른 실험구에 비해 높은 발현량을 확인하였고, 산소소비량은 9℃ 및 12℃에서 21℃에 비해 낮았다. 이러한 결과는 넙치 종자의 장거리 수송을 위한 수온자료로 활용할 수 있다