Prevalence of necrotizing hepatopancreatitis in female broodstock of white shrimp Penaeus vannamei with unilateral eyestalk ablation and hormone injection

The present study analyzed the relationship between unilateral eyestalk ablation and steroid hormone injection in female white shrimp Penaeus vannamei, the prevalence of necrotizing hepatopancreatitis (NHP) caused by the intracellular rickettsia-like bacterium NHP-B. Two simultaneous bioassays determined the onset and development of NHP in broodstock. Wet-mount analysis, conventional histopathology, and in situ hybridization with an NHP-B-specific DNA probe were used to assess the prevalence and degree of severity of NHP and to confirm NHP-B infection. Wet-mount and histopathological results showed that females with unilateral eyestalk ablation had a 64% prevalence of NHP at grades 2 and 4, while females receiving the hormone injection showed a 23% prevalence of NHP at grades 3 and 4; control shrimp injected with phosphate-buffered saline (PBS) displayed a 9% prevalence of NHP at grade 3, whereas nonablated controls showed no signs of disease. The rickettsia-like specific DNA probe demonstrated a positive hybridization signal in NHP-B, and the hepatopancreas, the target tissue for the bacterium, showed a strong positive signal. Significant differences (P < 0.05) were found in females with unilateral eyestalk ablation compared with nonablated controls, in hormone-injected females compared with PBS-injected controls, and in females with unilateral eyestalk ablation compared with the hormone injection group. We conclude that unilateral eyestalk ablation enhances NHP disease prevalence in broodstock reared under maturation conditions.