LAUSR

This study evaluated the hematological, biochemical, and histopathological responses of sorubim Pseudoplatystoma spp., experimentally infected with Lactococcus garvieae. Sorubim juveniles (n = 66; 21.3 ± 5.5 g; 17.1 ± 1.3 cm) were infected with L. garvieae by coelmatic inoculation (1.5 × 108 CFU mL−1) and sampling to 1, 3, 7, 14, and 21 days post-inoculation (dpi) for evaluation of hematological, biochemical parameters. Histopathological data of the spleen and kidney were estimated according to the histological alteration index (HAIn). Additionally, a decrease of hematocrit (1, 3, and 14 dpi), hemoglobin, and count of erythrocytes (3, 14, and 21 dpi), blood glucose (3 dpi), and proteinemy (14 dpi) were observed. Monocytes decreased at 7, 14, and 21 dpi; neutrophils at 3, 7, and 21 dpi; and lymphocytes at 21 dpi. Edema, hyperemia, hemorrhage, inflammatory infiltrate, and necrosis were the major histological changes observed in the spleen and kidney. HAIn was higher at 7 to 14 dpi in the spleen. Edema, hyperemia, and hyperplasia with hypertrophy of melanomacrophage centers (MMCs) associated with mild focal necrosis areas, particularly in white pulp, were observed. In the head kidney, it was observed that MMCs and melanomacrophages surrounded the capillaries and dispersed inside the sinusoidal capillaries network. Internalized bacteria by macrophages were commonly observed at 3 to 7 dpi. Tubular neogenesis characterized by nephrogenic bodies and rare MMCs at 21 dpi was observed. The experimental infection with L. garvieae caused significant hematological and biochemical responses. Pathological manifestations are closely related to the spleen and head kidneys mainly represented by hyperplasia and hypertrophy of melanomacrophage centers and mild necrosis areas.