Pathological aspects of experimental infection of Lactococcus garvieae in European Sea Bass (Dicentrarchus labrax L.): Clinical, hematological, and histopathological parameters

This study, it was aimed to examine the clinical, hematological, and histopathological aspects of lactococcosis induced in European sea bass (Dicentrarchus labrax), which was experimentally infected with Lactococcus garvieae. For this purpose, the infection was induced intraperitoneally with L. garvieae strain (108 CFU/mL), and blood samples were collected from the infected fish on different days (6, 18, 26, 31, 36, 44, and 48th) of infection. The morphological structures, erythrocyte and leukocyte count, hematocrit value, sedimentation rate, and coagulation time of the blood cells in the collected samples were calculated. As a result of the infection, while there was a decrease in erythrocyte count, hematocrit value, and coagulation rate, in addition to changes in the morphological structure of blood cells, it was determined that there was a significant increase in the leukocyte count and sedimentation rate. Furthermore, histopathological examination was also performed in the organs of infected fish such as the brain, liver, spleen, kidney, heart, gill, and intestine. Histopathologically, in the infected sea bass, while hemorrhage, diffuse necrosis, and hyaline droplets were detected in the granular brain tissue, hyperemia and hemorrhage were noted in the liver and spleen, and widespread necrosis in the hematopoietic tissue of the kidney, in the gills intensive hyperplasia, an increase in the goblet cell were detected. Although there are studies on lactococcosis in various marine fish species around the world, the infection of L. garvieae in farmed sea bass and various parameters and pathological aspects were investigated in detail for the first time in this study. L. garvieae was determined to have clinical significance for European sea bass with a high economic value.