Harveyi clade species were thought to be the major pathogens threatening the health development of the aquaculture industry globally. Multiple Harveyi clade species have been implicated in the aquatic diseases from different countries, causing mortalities up to 100% of some common economic aquatic animals such as Litopenaeus vannamei and tilapia, which are widely farmed around the world ( Tran et al., 2013 Prithvisagar et al., 2021).

The colloquially “Harveyi clade” is considered as the most severely pathogenic Vibrio cluster of aquatic organisms, capable of causing more than 50 different types of aquatic animal diseases and potentially disrupting the aquaculture system due to its high mortality ( Del Gigia-Aguirre et al., 2017 Wang et al., 2021).

The genus Vibrio has over 100 species that have been classified into 14 clades ( Ruwandeepika et al., 2012 Romalde et al., 2014). A recent evolutionary event within the genus Vibrio occurred 39 million years ago ( Sawabe et al., 2007). are curved rods of Gram-negative bacteria composed of halophile species with significant biodiversity and present naturally in marine, estuarine, and freshwater systems worldwide ( Thompson et al., 2004 Baker-Austin et al., 2017 Baker-Austin et al., 2018 Hackbusch et al., 2020). These results provide substantial data to support further studies on the identification and genetic and metabolic diversity of Harveyi clade isolates in mariculture systems in China. A proportion of 61.8% of the isolates presented a multiple antibiotic resistance index (MARI) lower than 0.1, indicating that the risk of antibiotic resistance transmission of most of the Harveyi clade is low in mariculture systems in China. The isolates showed a varied tolerance to 11 antibiotics. At the metabolic level, the physiological and biochemical experiments revealed that all the Harveyi clade isolates were positive for oxidase and negative for melibiose. ST327 ranked first, accounting for 11.5% of the total number of isolates (22 out of 192), followed by ST215 with 6.25%, while 63 STs included single isolates. The population of these isolates was composed of 95 sequence types (STs), of which 92 STs were newly identified, indicating a high degree of genetic diversity. Based on the multilocus sequence analysis (MLSA) of housekeeping genes ( gyrB, pyrH, recA, and atpA), 192 Harveyi clade isolates were rapidly and accurately classified into 10 species. The isolates had a significant interspecific genetic and antibiotic resistance diversity. Therefore, we conducted an extensive phenotypic and antibiotic resistance study, as well as phylogenetic and molecular typing of 192 isolates of the Harveyi clade collection from 2000 to 2020 with a typical interannual difference from a coastal area in China.

It is difficult to provide specific data on taxa of the Harveyi clade for biological research and prevention strategies. Vibrio bacteria, particularly members of the Harveyi clade, are the most important pathogens of aquatic organisms that cause significant economic losses in the world. 3Laboratory for Marine Fisheries Science and Food Production Processes, Qingdao National Laboratory for Marine Science and Technology, Qingdao, China.2Key Laboratory of Maricultural Organism Disease Control, Yellow Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Qingdao, China.1College of Marine Life Sciences, Ocean University of China (OUC), Qingdao, China.Hao Kang 1,2†, Yongxiang Yu 2,3†, Meijie Liao 2,3*, Yingeng Wang 2,3*, Guanpin Yang 1, Zheng Zhang 2,3, Bin Li 2,3, Xiaojun Rong 2,3 and Chunyuan Wang 2,3

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