Aquaculture production has expanded significantly in recent years. Nonetheless, infectious diseases remain a key concern, preventing future escalation. L. garvieae, a warm-water pathogen, is one of the main issues for aquaculture in the Mediterranean area. It is the aetiological agent of lactococcosis in freshwater and marine farmed fish, a disease marked by hyperacute hemorrhagic septicemic infections. The Mediterranean’s moderate climate and higher water temperatures, due to the global warming, contributed to the emergence of lactococcosis outbreaks in this region. Virulence factors seem to act as main actors of L. garvieae pathogenicity. One of these factors is the capsule: the link between the pathogenicity of the strains and the capsule is not fully understood. However, differences in the capsule’s polysaccharide composition might explain the virulence or non-virulence of some strains. Other factors are hemolysins because of their lytic actions. Hemolysins and their role in virulence and disease have been examined at the molecular level in various pathogenic bacteria, including L. garvieae. By generating pores and altering phospholipid structures in the membrane, their enzymatic actions promote the lysis of red blood cells and phagocytes. On blood agar, L. garvieae displayed hemolytic activity, and three hly genes were found in the genome: hly1, hly2, and hly3. In the context of the European project SUPERTROUT (Improving SUstainability and PERformance of aquaculture farming systems: breeding for lactococcosis resistance in rainbow TROUT), aimed at sustaining small-scale farming systems of trout production in the Mediterranean area by using an innovative approach to control lactococcosis, archivial strains collected in the Countries participating to the project (Italy, Spain, Greece and Turkey) were characterized for hemolisin genes and for the capsule cluster genes.