Hygiene management is important to prevent red sea bream iridovirus transmission between net pens: Insights from a case study assessing cross-contamination in a fish farm

Kawato, Yasuhiko; 河東, 康彦; カワトウ, ヤスヒコ; Takada, Yuzo; 髙田, 優三; タカダ, ユウゾウ; Matsuyama, Tomomasa; 松山, 知正; マツヤマ, トモマサ; Honryo, Tomoki; Shirakashi, Sho; Masuma, Shukei; 升間, 主計; マスマ, シュケイ

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Hygiene management is important to prevent red sea bream iridovirus transmission between net pens: Insights from a case study assessing cross-contamination in a fish farm

https://doi.org/10.57348/0002016036

名前 / ファイル	ライセンス	アクション
fra_k_53_99.pdf (180.8 KB)

アイテムタイプ

紀要論文 / Departmental Bulletin Paper(1)

公開日

2026-04-01

タイトル

Hygiene management is important to prevent red sea bream iridovirus transmission between net pens: Insights from a case study assessing cross-contamination in a fish farm

言語

eng

キーワード

言語

主題Scheme

Other

主題

red sea bream iridovirus; RSIV; cross-contamination; aquaculture biosecurity; hygiene management

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資源タイプ識別子

http://purl.org/coar/resource_type/c_6501

資源タイプ

departmental bulletin paper

ID登録

10.57348/0002016036

ID登録タイプ

JaLC

著者

河東, 康彦

WEKO 876
e-Rad 90634220

en	Kawato, Yasuhiko（Organizational）
ja	河東, 康彦（Organizational）
ja-Kana	カワトウ, ヤスヒコ（Organizational）

Search repository

髙田, 優三

WEKO 1163
e-Rad 20971394

en	Takada, Yuzo（Organizational）
ja	髙田, 優三（Organizational）
ja-Kana	タカダ, ユウゾウ（Organizational）

Search repository

松山, 知正

WEKO 688
e-Rad 20372021

en	Matsuyama, Tomomasa（Organizational）
ja	松山, 知正（Organizational）
ja-Kana	マツヤマ, トモマサ（Organizational）

Search repository

Honryo, Tomoki
Shirakashi, Sho
升間, 主計

WEKO 2036
e-Rad 80426311

en	Masuma, Shukei（Organizational）
ja	升間, 主計（Organizational）
ja-Kana	マスマ, シュケイ（Organizational）

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内容記述タイプ

Abstract

内容記述

Red sea bream iridovirus (RSIV) infection, which is currently listed as a notifiable disease by the World Organization for Animal Health (WOAH), has caused significant economic damage in Japanese mariculture since the 1990s. Although formalin-inactivated vaccines are commercially available to control RSIV outbreaks, fish farmers do not use the vaccine when the vaccination cost is not acceptable compared to the market value of a given cultured fish. Therefore, basic biosecurity management such as hygiene procedures could be important to control RSIV outbreak. Nevertheless, in the case of mariculture using net pens or cages which is defined as semi-open system aquaculture by WOAH, the hygiene procedures have been considered less effective than those applied to land-based aquaculture because there is no physical barrier to prevent pathogens from moving via environmental water between aquaculture units. Our latest study suggested that RSIV transmission via seawater is highly associated with the distance between net pens and that the environmental water could function as a potential barrier to prevent viral transmission. Hence, we hypothesized that the biosecurity management could effectively reduce the risk of RSIV transmission even in semi-open system aquaculture where environmental water can move freely.
　For implementing aquaculture biosecurity, the significance of fomite transmission in fish farms has been described, especially in salmonid aquaculture. However, the studies for aquaculture biosecurity are based on epidemiological data and questionnaire results for fish farms. To the best of our knowledge, there is no previous study that directly assessed the intensity of contamination in each aquaculture equipment associated with the fomite transmission. In the present study, cross-contamination of RSIV in aquaculture equipment and facilities in a fish farm where RSIV outbreak occurred was investigated by surface swabbing tests and an environmental DNA technique. Based on the results in this case study, we assessed the risk factors for transmission of RSIV between net pens to identify an effective hygiene procedure in the semi-open system aquaculture.
　The investigation was performed in a fish farm where the RSIV outbreak occurred between September and October in 2022. The outbreak was initiated from juvenile red sea bream Pagrus major and transmitted to juvenile Pacific bluefin tuna Thunnus orientalis. Our investigation during the RSIV outbreak in the fish farm demonstrated that landing nets and gloves associated with collecting dead fish (carcasses) were highly contaminated with RSIV. The viral load of the contaminated equipment was > 108 copies of the RSIV genome. Because the equipment for collecting fish carcasses were used at all net pens without disinfection, the risk of fomite transmission was considered to be higher than the transmission via environmental seawater if the distances among net pens are appropriately secured. On the other hand, we could not request fish farmers to undertake a strict hygiene procedure that is often implemented in land-based aquaculture because disinfection on boats is generally difficult owing to limited space of boats and the direct influences of weather. Therefore, we proposed mitigation measures against RSIV transmission between net pens and the following actions were initiated in the fish farm. A daily operation for collecting dead fish started from the net pen where the disease had not occurred and moved to the net pen where RSIV outbreak occurred to ensure that RSIV was not transmitted to the clean net pens by cross-contamination. In addition, the landing nets used for collecting fish carcasses were disinfected at the end of each day to avoid carryover of the virus to the following day. As a result, RSIV was not transmitted to the clean net pens in the fish farm for more than 30 days. However, once the RSIV outbreak occurred in the net pen upstream in the operation for collecting dead fish, RSIV was transmitted to all net pens in one week, suggesting that the transmission was caused by cross-contamination.
　This study indicated that appropriate hygiene management is important to reduce the risk of RSIV transmission between net pens, even in semi-open system aquaculture. However, careful attention to the sequence of operation could not be a sufficient strategy when the RSIVD outbreak suddenly occurred in the upstream of operation as shown in the present study. For the future study, we need to seek disinfection procedures targeting the high-risk equipment such as landing nets and gloves for collecting dead fish, which can be undertaken on the boat considering cost-effective and labor-efficient method. We believe that the present study represents the first step for implementing appropriate biosecurity management in semi-open system aquaculture, which could be expanded for other viral or bacterial infections in aquaculture.
　This study was supported by a grant from the Ministry of Agriculture, Forestry and Fisheries of Japan (grant number JPJ007159).

言語

書誌情報

ja : 水産研究・教育機構研究報告
en : Bulletin of Japan Fisheries Research and Education Agency

巻 53, p. 99-101, ページ数 3, 発行日 2026-03-25

出版者

水産研究・教育機構

言語

出版者

Japan Fisheries Research and Education Agency

言語

ISSN

収録物識別子タイプ

PISSN

収録物識別子

2758-3953

書誌レコードID

収録物識別子タイプ

NCID

収録物識別子

AA12767505

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2026-04-01 08:01:11.656965

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