Influence of nitrogen compounds and water temperature on association of Lactococcus garvieae to gill tissue of rainbow trout in Lactococcosis

Lactococcosis is an infectious septicemic disease in fish. In the present study ability of Lactococcus garvieae to adhere to the gill tissue of rainbow trout (Oncorhynchus mykiss) was evaluated. The overall objective was to study the interaction between Lactococcus garvieae and rainbow trout during the infection process. Experiments were additionally carried out to assess the influence of water quality (ammonia, nitrate) and temperature on the adhesion process of the bacterial cells. For that purpose, an applied model of experimental infections (gill perfusion model) was adopted, offering a number of advantages compared to other in vitro as well as in vivo models. Bacteriological and histo-pathological results showed that the bacterium is capable of adhering to gill tissue and could be as a portal of entry to body of fish. It was also observed that adherence of Lactococcus garvieae was affected by a number of factors. These were immersion of the gill arches in water to which ammonia and nitrate were added and elevated temperature. All of them increased the bacterial adhesion ability.