Abstract

Aquaculture production has increased in a considerable amount in the last three decades and many microbial diseases have been reported to cause mass mortality in fish as well as economic losses. In recent years, it has been reported that many opportunistic pathogens such as Shewanella cause infections in fish. In the present study, the causative microbial agent of lens atrophy and its pathogenesis were determined by different microbiological methods, Whole Genome Sequencing (WGS) analysis, and the anatomical examination of the lens and eye, and data comparison were performed.^1-5

Strain S-1 was identified with 16S rRNA gene region sequencing as well as whole-genome analysis.⁶ The pathogenicity of this strain was assessed based on the histopathological examination of the eyes, lens, muscle, brain, liver, kidney, spleen, and gills. The lens, brain, and eyes of the fish were also examined morphologically.

Strain S-1 was determined to belong to the genus Shewanella and was considered to be a putative novel Shewanella species according to genome-based delineation. While we determined that the lens had atrophied at a level ranging from 30% to 40%, no severe lesions were detected in other organs. Fish that hatched in the same period were bred under uniform feeding and management conditions for a month. Monitoring data revealed that, at the end of this 1-month period, the growth rate and feed conversion rate of the diseased fish were significantly lower than those of the healthy group. Based on anatomical, microbiological, histopathological examinations, it was demonstrated for the first time that Shewanella sp. strain S-1 infection caused lens atrophy in fish.

Acknowledgments

We thank Dr. Izzet Burcin Saticioglu and Dr. Muhammed Duman for their contributions to conducting molecular and genomic analyses.

*Presenting author

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