In aquaculture, several criteria should be considered to select an appropriate probiotic, including the aquatic origin and safety of the strain and its ability to modulate the host immune response. The properties and effects of probiotics are strain-specific and some factors such as viability, dose and duration of diet supplementation may regulate their immunomodulatory activities. In this study, we assessed the in vitro effect of eight heat-inactivated and viable lactic acid bacteria (LAB) of aquatic origin belonging to the genera Enterococcus, Lactobacillus, Lactococcus, Leuconostoc, Pediococcus and Weissella on the viability and innate immune response of turbot (Scophthalmus maximus L.) leucocytes. Head-kidney leucocytes were incubated with viable and heat-inactivated Lat different concentrations. After incubation, the viability of leucocytes was evaluated using colorimetric assays (MIT and LDH) and flow cytometry (annexin V/propidium iodide). Heat-inactivated Lshowed no cytotoxic effect while viable Lexerted variable influence on apoptosis of turbot phagocytes and lymphocytes. Leucocyte respiratory burst activity and phagocytosis were also differentially activated, as viable Lstimulated leucocytes more efficiently than the heat-inactivated LAB. Our results suggest diverse strain-specific mechanisms of interaction between the evaluated Land turbot leucocytes. Furthermore, our work sets up in vitro systems to evaluate the effect of Las potential probiotics, which will be useful to develop efficient screening.