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

본 연구는 넙치를 인공사육 시설에서 육성할 때 나타나는 무안측 흑화(착색증)의 스트레스 관련 성을 확인하기 위해, 무안측에 체색이 없는 것(정상 그룹)와 체색이 있는 것(흑화 그룹)들 사이 스트레스 인자 비교 실험을 실시하였다. 본 실험에 사용된 실험어는 평균 전장 21.5±0.42 cm, 평균 무게 87.5±6.1 g였으며, 실험어의 무안측 착색면적률은 정상 그룹 0.63±0.12%, 착색증 그룹 16.7±4.7%였다. 분석한 스트레스 관련 인자는 혈중 GLU 및 TP, 코티졸 및 갑상선호르몬(FT3 & FT4) 농도 및 어체 성분(수분, 조단백, 조지방, 조회분)이었다. 실험 결과, 정상과 무안측 착색 넙 치에 있어 혈중 GLU 및 TP의 농도는 정상 형질보다 착색증 형질에서 유의하게 높게 나타났다. 혈 중 호르몬 농도에 있어 갑상선호르몬의 경우 정상과 착색증 그룹 사이에는 유의차를 찾아볼 수 없지만, 코티졸은 착색증 그룹이 정상 그룹에 비해 유의하게 높게 나타났다. 어체 중 영양 성분의 경우, 수분과 회분은 그룹 간 유의차가 없었지만, 조단백은 착색증 그룹이 정상보다 다소 낮으며, 조지방은 정상보다 유의하게 높았다. 이상의 스트레스 인자를 통한 정상과 착색증 그룹 간 비교 를 통해 알 수 있듯, 양식산 넙치의 착색증은 만성적이 약한 스트레스에 관련되어 있을 가능성이 높은 것으로 확인되었다.

Garlic (Allium sativum) is known to have antimicrobial effects but there are few data on its effects against fish pathogenic bacteria. This study was conducted for possible development of natural food antimicrobials from garlic extracts, particularly allicin. The filter sterilized, aqueous extract of garlic was tested for its ability to inhibit the growth of 7 fish pathogenic bacteria (E. tarda, V. ichthyoenteri, V. harveyi, P. damselae, S. iniae, S. parauberis, L. garviae) using the disc diffusion test, minimum inhibitory concentration test, and minimum bacteriocidal concentration test. The garlic extract inhibited growth and killed most of the organisms tested. The disc diffusion test was performed using garlic extracts (100%, 50%, 25%, 10%, each 20㎍), and MIC test was also performed using a diluted concentration of garlic extracts (488 - 250,000 ㎍/㎖). According to the results, garlic extracts exhibited antimicrobial activity against all of seven bacteria, and these results suggest that this garlic extract can be used as an antimicrobial substance against fish bacterial diseases in the fish industry.

Antibiotic Detection Kit (Combination I), a lateral flow immunoassay (LFIA) developed for detecting antibiotic residues in milk, was utilized for the analysis of antibiotic residues in the muscle tissue of olive flounder. After 5-h treatment of samples by placing them in water dosed with sulfadimethoxine (SDM; 200 g/ton water), the residue depletion of SDM was investigated in 25 cultured olive flounders (Paralichthys olivaceus). Muscles from fish were sampled before treatment and on the 1st, 2nd, 3rd, 4th and 5th days after treatment. The concentration of SDM in the muscle was then determined by LFIA. The absorbance ratio of the sample to the control blank (Bs/Bo) was employed as an index to determine the residue in olive flounder muscle. To investigate the recovery rate, standard solutions were added to muscle samples to obtain final concentrations of 25 and 50 ng/mL in the muscle. The recovery rates of all spiked samples were >96.6% of the spiked value. SDM was detectable in the muscle of fish treated with the drug until the 1st day of the withdrawal period. The present study shows that the LFIA can be easily adopted to detect SDM residues in the tissue of farmed fish.