Clinical and histopathological evidence of Hepatobacter penaei in Litopenaus vannamei culture with high mortality

Abstract

With the appearance of high mortalities in traditional cultivation of Pacific white shrimp (Litopenaus vannamei), the objective was to evaluate the health in semi-intensive nurseries in Mossoró/RN. A random sample of 200 shrimp was collected for presumptive clinical and histopathological examination of the hepatopancreas. Histologically, the hepatopancreatic fragments were evaluated for the presence of intracytoplasmic bacteria, and scores (1-4) were assigned according to the degree of severity of the lesions (DS). Morbidity percentages of 89.5% of shrimp infected with the bacterium Hepatobacter penaei were recorded. Hemolymph clotting time did not prove to be a good parameter to diagnose individuals with necrotizing hepatopancreatitis. The affected individuals presented melanized lesions; 45.5% presented focal to diffuse necrosis in the abdominal segments, and the pleopods presented an expansion of chromatophores only in the most evolved cases of the infection, with 73% presenting uropods with expanded chromatophores. In the hepatopancreas, it was found that 57.5% had tubules with a significant reduction in lipid levels, 66.5% had DS 3 indicating the transition phase of the disease, and 23% had DS 4 considering the chronic phase. Absence of cytoplasm was observed in B cells with chromatin condensation. It is concluded that abiotic factors such as salinity and high temperatures favored the virulence of the pathogen in marine shrimp ponds, triggering a high mortality rate.