Lactococcus garvieae is a major fish pathogen leads to haemorragic septicemia in many fish species. Present study was designed to determine and compare differences in susceptibilities of some important fish species to L. garvieae. Rainbow trout (Oncorhynchus mykiss), Black Sea trout (Salmo trutta labrax; synonym, Salmo coruhensis), turbot (Psetta maxima), and sea bass (Dicentrarchus labrax) were kept at different temperature ranges (12-23 degrees C) for 30 days and challenged by intraperitoneal (i.p.) injection and immersion (imm) with L. garvieae (Lgper), isolated from rainbow trout and ATCC49156 strain. Bacteria were ranged between 1.7x10(5) - 2x10(6) colonies forming unit (cfu) fish(-1) in experiments. As a result of the experiments, Lgper strain had high virulence for rainbow trout, with 98% mortality when challenged by i.p. injection. Rainbow trout and Black Sea trout tested at the lower temperature (12 degrees C) were less susceptible (max. mortality 16%) to L. garvieae. These two fish species had similar susceptibilities to L. garvieae (P>0.05). There was no mortality or any clinical signs when turbot and sea bass were challenged with L. garvieae. The results of the study generate important source in controlling of possible lactococcosis outbreaks in aquaculture industry.