Piscine lactococcosis is a significant threat to fish populations worldwide, caused by three lactococcosis-causing bacteria (LCB): Lactococcus garvieae, L. petauri, and L. formosensis. These bacteria are phenotypically and genetically similar, leading to widespread misidentification. Recent studies have shown that L. petauri and L. formosensis are distinct from L. garvieae and should be considered separate species. Whole-genome sequencing (WGS) and specific molecular assays, such as qPCR targeting a glycosyltransferase gene, can accurately distinguish these species. However, traditional methods like MALDI-TOF MS, API 20 Strep, and FAME analysis are insufficient for accurate identification. The three LCB species have overlapping host and geographic ranges but differ in host specificity, regional prevalence, and antimicrobial susceptibility, affecting disease management. L. petauri is the most prevalent LCB in the Americas, particularly in rainbow trout and catfish farming. Antimicrobial resistance is a growing concern, with L. petauri showing resistance to tetracycline and other antibiotics. The development of species-specific diagnostic tools, such as the Lp-p6 qPCR assay, is crucial for accurate identification and management of lactococcosis. Proactive measures, including vaccination and improved biosecurity, are necessary to control the disease. Understanding the genetic diversity and antimicrobial resistance profiles of LCB will aid in developing effective treatment strategies and preventing the spread of the disease.Piscine lactococcosis is a significant threat to fish populations worldwide, caused by three lactococcosis-causing bacteria (LCB): Lactococcus garvieae, L. petauri, and L. formosensis. These bacteria are phenotypically and genetically similar, leading to widespread misidentification. Recent studies have shown that L. petauri and L. formosensis are distinct from L. garvieae and should be considered separate species. Whole-genome sequencing (WGS) and specific molecular assays, such as qPCR targeting a glycosyltransferase gene, can accurately distinguish these species. However, traditional methods like MALDI-TOF MS, API 20 Strep, and FAME analysis are insufficient for accurate identification. The three LCB species have overlapping host and geographic ranges but differ in host specificity, regional prevalence, and antimicrobial susceptibility, affecting disease management. L. petauri is the most prevalent LCB in the Americas, particularly in rainbow trout and catfish farming. Antimicrobial resistance is a growing concern, with L. petauri showing resistance to tetracycline and other antibiotics. The development of species-specific diagnostic tools, such as the Lp-p6 qPCR assay, is crucial for accurate identification and management of lactococcosis. Proactive measures, including vaccination and improved biosecurity, are necessary to control the disease. Understanding the genetic diversity and antimicrobial resistance profiles of LCB will aid in developing effective treatment strategies and preventing the spread of the disease.