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Diseases of Aquatic Organisms

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DAO 136:227-234 (2019)  -  DOI:

Identification of Chryseobacterium spp. isolated from clinically affected fish in California, USA

Fernanda de Alexandre Sebastião1, Thomas P. Loch2, David P. Marancik3, Matt J. Griffin4, Joe Maret5, Christine Richey5, Esteban Soto1,*

1Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA 95616, USA
2Department of Fisheries and Wildlife, College of Agriculture and Natural Resources; Department of Pathobiology and Diagnostic Investigation, College of Veterinary Medicine, Michigan State University, East Lansing, MI 48823, USA
3Department of Pathobiology, School of Veterinary Medicine, St. George’s University, True Blue, Grenada
4Department of Pathobiology and Population Medicine, College of Veterinary Medicine, Mississippi State University, 127 Experiment Station Road PO Box 197, Stoneville, MS 38776, USA
5California Department of Fish and Wildlife, Rancho Cordova, CA 95670, USA
*Corresponding author:

ABSTRACT: Chryseobacterium spp. (Family Flavobacteriaceae) are emergent fish pathogens in Europe, Asia and North America. In 2016-2017, 7 bacterial isolates were recovered from posterior kidney or spleen of cultured diseased rainbow trout Oncorhynchus mykiss (n = 1), green sturgeon Acipenser medirostris (n = 1), white sturgeon A. transmontanus (n = 2), blue ram cichlid Mikrogeophagus ramirezi (n = 1), and returning fall Chinook salmon O. tshawytscha (n = 2) from different freshwater systems. Bacterial colonies were visible after 24-48 h incubation at 20°C on agar media. Isolates were Gram-negative, rod-shaped, catalase and oxidase positive. Amplification and partial sequence analysis of the 16S rRNA and gyrB genes allocated the microorganisms to the genus Chryseobacterium sharing 97.2-99.6% similarity to 6 described Chryseobacterium spp. at the 16S rRNA locus, and 87.8-99.1% similarity at gyrB. Phylogenetic analyses in conjunction with percent sequence identity suggest some of the recovered isolates may represent novel Chryseobacterium subspecies or species. The pathogenicity of 5 isolates was evaluated experimentally in rainbow trout (n = 60), brown trout Salmo trutta (n = 60) and white sturgeon (n = 36) in flow-through freshwater at 18°C. Approximately 107 CFU fish-1 was injected in the epaxial musculature of anesthetized animals. Limited mortality was observed and no bacteria were recovered from dead or moribund fish post-challenge. Thirty days post-challenge, survivors were euthanized and multiple tissues were collected and fixed for histological analysis. No consistent histopathological changes were observed in challenged or control fish. While results suggest the recovered Chryseobacterium spp. may be opportunistic pathogens, further research is warranted to better understand the role of these bacteria in fish disease.

KEY WORDS: Chryseobacterium · Flavobacterium · 16S rRNA · gyrB · North America

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Cite this article as: Sebastião FdA, Loch TP, Marancik DP, Griffin MJ, Maret J, Richey C, Soto E (2019) Identification of Chryseobacterium spp. isolated from clinically affected fish in California, USA. Dis Aquat Org 136:227-234.

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