Aquaculture production has developed rapidly in recent decades and is one of the major contributors to animal protein (Tadese et al., 2021). Global aquaculture production increased from 35.5 million tons in 2000 to 82.1 million tons in 2018 with an average annual growth rate of 4.51% (See et al., 2021). However, a fast-developing production has led to aquatic environmental issues and disease outbreaks. Fish diseases caused by microbial pathogens are more and more serious and have led to substantial economic growth losses (He et al., 2020;Ramesh & Souissi, 2018). Streptococcus agalactiae, known as group B streptococcus (GBS), is a severe Gram-positive pathogenic bacterium (Dong et al., 2021). It is widely distributed in the environments worldwide and can infect human beings, terrestrial animals and fish (Edwards & Baker, 2005;Pereira et al., 2010;Zhu et al., 2018). Some human and bovine S. agalactiae strains can infect tilapia under experimental conditions, but serotypes and sequence types of S. agalactiae isolates from different hosts have no evident genetic relatedness (

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