Clinical and histopathological evidence of Hepatobacter penaei in Litopenaus vannamei (Pacific white-shrimp) culture.

With the appearance of high mortalities in the traditional cultivation of Pacific white shrimp (Litopenaus vannamei), the objective was to evaluate the health in semi-intensive nurseries in Mossoró, Rio Grande do Norte, Brazil. A random sample of 200 shrimp was collected, with 50 shrimp sampled per month during the dry season (August to November), 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 was not suitable for diagnosing individuals with necrotizing hepatopancreatitis. The affected individuals presented melanized lesions, such as focal to diffuse necrosis in the abdominal segments (45.5%), 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. The absence of cytoplasm was observed in B cells with chromatin condensation. The findings suggest that abiotic factors, such as salinity (34.3‰ ± 2.78) and high temperatures (27°C ± 1.40), may have contributed to the pathogen's virulence in marine shrimp ponds, resulting in a high mortality rate. [ABSTRACT FROM AUTHOR]