Biochemical changes and drug residues in ascidian Halocynthia roretzi after formalin–hydrogen peroxide treatment regimen designed against soft tunic syndrome

Fisheries and Aquatic Sciences, Jul 2017

Soft tunic syndrome (STS) is a protozoal disease caused by Azumiobodo hoyamushi in the edible ascidian Halocynthia roretzi. Previous studies have proven that combined formalin–hydrogen peroxide (H2O2) bath is effective in reducing STS progress and mortality. To secure target animal safety for field applications, toxicity of the treatment needs to be evaluated. Healthy ascidians were bathed for 1 week, 1 h a day at various bathing concentrations. Bathing with 5- and 10-fold optimum concentration caused 100% mortality of ascidians, whereas mortality by 0.5- to 2.0-fold solutions was not different from that of control. Of the oxidative damage parameters, MDA levels did not change after 0.5- and 1.0-fold bathing. However, free radical scavenging ability and reducing power were significantly decreased even with the lower-than-optimal 0.5-fold concentration. Glycogen content tended to increase with 1-fold bathing without statistical significance. All changes induced by the 2-fold bathing were completely or partially restored to control levels 48 h post-bathing. Free amino acid analysis revealed a concentration-dependent decline in aspartic acid and cysteine levels. In contrast, alanine and valine levels increased after the 2-fold bath treatment. These data indicate that the currently established effective disinfectant regimen against the parasitic pathogen is generally safe, and the biochemical changes observed are transient, lasting approximately 48 h at most. Low levels of formalin and H2O2 were detectable 1 h post-bathing; however, the compounds were completely undetectable after 48 h of bathing. Formalin–H2O2 bathing is effective against STS; however, reasonable care is required in the treatment to avoid unwanted toxicity. Drug residues do not present a concern for consumer safety.

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Biochemical changes and drug residues in ascidian Halocynthia roretzi after formalin–hydrogen peroxide treatment regimen designed against soft tunic syndrome

Lee et al. Fisheries and Aquatic Sciences Biochemical changes and drug residues in ascidian Halocynthia roretzi after formalin- hydrogen peroxide treatment regimen designed against soft tunic syndrome Ji-Hoon Lee 0 Ju-Wan Kim 0 Yun-Kyung Shin 1 Kyung-Il Park 0 Kwan Ha Park 0 0 Department of Aquatic Life Medicine, College of Ocean Science and Technology, Kunsan National University , 558 Daehak-ro, Miryong-Dong, Gunsan City, Jeonbuk 54150 , Republic of Korea 1 Southeast Sea Fisheries Institute, National Institute of Fisheries Science , Youngwun-Ri 361, Sanyang-Eup, Tongyeong City, Kyungnam , Republic of Korea Soft tunic syndrome (STS) is a protozoal disease caused by Azumiobodo hoyamushi in the edible ascidian Halocynthia roretzi. Previous studies have proven that combined formalin-hydrogen peroxide (H2O2) bath is effective in reducing STS progress and mortality. To secure target animal safety for field applications, toxicity of the treatment needs to be evaluated. Healthy ascidians were bathed for 1 week, 1 h a day at various bathing concentrations. Bathing with 5- and 10-fold optimum concentration caused 100% mortality of ascidians, whereas mortality by 0.5- to 2.0-fold solutions was not different from that of control. Of the oxidative damage parameters, MDA levels did not change after 0.5- and 1.0-fold bathing. However, free radical scavenging ability and reducing power were significantly decreased even with the lower-than-optimal 0.5-fold concentration. Glycogen content tended to increase with 1-fold bathing without statistical significance. All changes induced by the 2-fold bathing were completely or partially restored to control levels 48 h post-bathing. Free amino acid analysis revealed a concentration-dependent decline in aspartic acid and cysteine levels. In contrast, alanine and valine levels increased after the 2-fold bath treatment. These data indicate that the currently established effective disinfectant regimen against the parasitic pathogen is generally safe, and the biochemical changes observed are transient, lasting approximately 48 h at most. Low levels of formalin and H2O2 were detectable 1 h post-bathing; however, the compounds were completely undetectable after 48 h of bathing. Formalin-H2O2 bathing is effective against STS; however, reasonable care is required in the treatment to avoid unwanted toxicity. Drug residues do not present a concern for consumer safety. Ascidians; Formalin-hydrogen peroxide combination; Toxicity; Biochemical parameters; Drug residues; Soft tunic syndrome Background Soft tunic syndrome (STS) in the ascidian Halocynthia roretzi has markedly reduced production of this edible invertebrate. Official figures indicate a gradual decrease in production to less than a half of the peak yearly production of approximately 22,500 t in 1995 (Kumagai et al. 2010) . The cause of STS is infection with a protozoal parasite Azumiobodo hoyamushi, which leads to softening of the rigid cellulose-protein tunic structure (Dache et al. 1992) without affecting the cellulose fiber structure itself (Kimura et al. 2015) . Highly active protease enzymes are produced and excreted from A. hoyamushi cells (Jang et al. 2012) . Although the disease spreads very rapidly, safe and effective measures have not been established to control the spread of STS in farms. Chemical biocides are the first line of preventive measures against infective organisms in the absence of a practical method to deal with the infection. Different classes of biocidal agents have been tested, and formalin, H2O2, bronopol, povidone iodine, and NaOCl were found effective against the causative parasite (Park et al. 2014; Lee et al. 2016; Kumagai et al. 2016) . The combination of two anti-infective chemicals, formalin and H2O2, was the most promising choice of treatment owing to their synergistic efficacy (Park et al. 2014) . Detailed results from treatment trials were published in a previous issue of this journal (Lee et al. 2016) , and this paper thus constitutes an important counterpart companion to it. Bathing ascidians with formalin and H2O2 suggested a possible use for the combination in treating infected ascidians; however, the possible side effects, except mortality, have not been examined. Certain side effects are expected, considering the non-selective mechanisms of action of these agents. The degree and recovery from toxicity should be considered in deciding the value of a treatment regimen. To determine the toxicity and safety of the formalin–H2O2 treatment, overall mortality, biochemical changes, and drug residue levels were assessed after a 1-week bathing treatment schedule in healthy ascidians. Methods Chemicals Formalin and H2O2 were purchased from Sigma (St. Louis, MO, USA), and actual concentrations were assessed before use by HPLC–UV (Soman et al. 2008) and peroxidase–H2O2 analysis kit (Cell Biolabs, San Diego, CA), respectively. All other reagents were purchased from Sigma if not sp (...truncated)


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Ji-Hoon Lee, Ju-Wan Kim, Yun-Kyung Shin, Kyung-Il Park, Kwan Ha Park. Biochemical changes and drug residues in ascidian Halocynthia roretzi after formalin–hydrogen peroxide treatment regimen designed against soft tunic syndrome, Fisheries and Aquatic Sciences, 2017, pp. 12, Volume 20, Issue 1, DOI: 10.1186/s41240-017-0058-8