Page 67 - 《渔业研究》2025年第5期

608 渔 业 研 究 第 47 卷

Isolation, identification, and in vitro characterization of Miamiensis avidus from
large yellow croaker (Larimichthys crocea)

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1,4
1,2
3
1,4
XUE Qianxi ，GUO Xiang ，YUAN Jiahao ，WEI Haiyun ，HUANG Guangliang ，
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ZHUO Yuchen ，CHEN Xinhua 1,4* ，QIN Pan 1,4*
(1. Key Laboratory of Marine Biotechnology of Fujian Province, Fuzhou 350002, China;
2. College of Life Sciences, Fujian Agriculture and Forestry University, Fuzhou 350002, China;
3. Fisheries Research Institute of Fujian, Xiamen 361013, China;
4. College of Marine Sciences, Fujian Agriculture and Forestry University, Fuzhou 350002, China;
5. Fishery Technology Promotion Station of Ningde City, Ningde 352100, China;
6. Freshwater Fisheries Research Institute of Fujian Province, Fuzhou 350002, China)

Abstract: [Background] The large yellow croaker (Larimichthys crocea) is a commercially valuable fish in
China, widely farmed in marine aquaculture. However, rapid growth in intensive farming has led to poorer wa-
ter quality and higher stocking densities, causing frequent disease outbreaks and economic losses. Notably, cili-
ate protozoan infections, especially scuticociliatosis, pose a significant threat. [Objective] This study aimed to
isolate and identify the ciliate causing scuticociliatosis in large yellow croaker and to understand its pathogenic
and biological traits, providing a basis for disease prevention and control. [Methods] In April 2025, fish co-in-
fected with trypanosomes and scuticociliates were collected from a net-cage farm in Ningde, China. The para-
sites were isolated, cultured, and identified via morphological and molecular analysis. A stable culture system
was developed to study the effects of temperature, pH, and salinity on ciliate growth. Drug sensitivity tests were
also performed to evaluate common aquaculture anti-parasitics. [Results] Morphological and phylogenetic ana-
lyses confirmed the ciliate as Miamiensis avidus. Temperature tests showed high sensitivity: all cells died at 0
℃ within 12 hours, and the population decreased at 30 ℃. Growth at 10 ℃ was slower than at 20 ℃, with no
significant difference at 25 ℃, indicating susceptibility to temperatures above 25 ℃. Salinity tests revealed all
cells died at salinity 0 within 12 hours, while growth at salinity 10 was slower than at salinity 30, with no signi-
ficant difference at salinity 20, indicating broad salinity tolerance. The parasite could grow at pH 5.5 and pH
9.0, though less than at pH 7.4, with no significant difference at pH 6.5 and pH 8.5, showing strong pH adaptab-
−1
ility. Drug sensitivity tests showed that carvacrol effectively eliminated M. avidus at a low dose (100 mg·kg ),
indicating its potential as a low-toxicity treatment. [Conclusion] The study confirms M. avidus as the cause of
scuticociliatosis in sub-adult large yellow croaker, explores environmental factors affecting parasite growth, and
identifies an effective low-dose treatment. These insights improve our understanding of M. avidus biology and
support sustainable scuticociliatosis management in large yellow croaker aquaculture.
Key words: large yellow croaker (Larimichthys crocea); Miamiensis avidus; species identification; in vitro
culture; environmental factors; drug sensitivity testing