| Summer flounder (Paralichthys dentatus) constitutes a major fishery in the coastal northeastern United States. Spurred by population declines, cultivation of summer flounder began in 1996, but expansion of culture efforts has been constrained by disease outbreaks. Flounder Infectious Necrotizing Enteritis (FINE) causes significant mortality of juvenile flounder. The disease is characterized by ascites, intestinal prolapse, and severe inflammation of the mesentery and posterior intestinal serosa, often resulting in intestinal rupture. FINE is caused by Vibrio harveyi, a bacterial pathogen of cultured marine fish and invertebrates. To better understand the immune response to FINE, recruitment and fluctuation of leukocytes within the summer flounder peritoneum were investigated during intraperitoneal challenge with V. harveyi. Consistent with the pathology of FINE, massive infiltration of large granular leukocytes was observed in coelom of flounder 24 hours after intra-peritoneal injection of live bacteria. In these fish, the number of lymphocytes doubled, though the number of B-cells was not significantly different from saline-injected animals. The large influx of granular cells resulted in a 15-fold increase in that population, decreasing the lymphocyte population from ∼65% to ∼20% of the total coelomic leukocyte pool. It is hypothesized that the influx of large granular leukocytes into the coelom of challenged animals may contribute significantly to the pathology of the disease. |
