First evidence of bright-red syndrome in Pacific white shrimp Penaeus vannamei broodstock from India

Abstract Objective This study aimed to isolate and characterize the putative causative agent of bright-red syndrome (BRS) in Pacific white shrimp Penaeus vannamei broodstock in India and to evaluate its pathogenic potential through controlled experimental infection. To the best of our knowledge, this is the first documented report of BRS in Pacific white shrimp broodstock from India. Methods A total of 200 broodstock shrimp were systematically examined for clinical signs consistent with BRS. Affected individuals were subjected to histopathological examination to assess tissue-level alterations. Diseased broodstock were screened for World Organization for Animal Health-listed crustacean pathogens, including white spot syndrome virus, infectious myonecrosis virus, infectious hypodermal and hematopoietic necrosis virus, Taura syndrome virus, yellow head virus, and acute hepatopancreatic necrosis disease, as well as the nonlisted pathogen Enterocytozoon hepatopenaei. Following negative screening results, detailed microbiological investigations were performed using selective culture media, and the predominant bacterial isolate was identified molecularly. Its pathogenicity was subsequently evaluated through a controlled immersion challenge experiment. Results Fourteen shrimp (7.0%) were identified as BRS-positive; they exhibited sluggish behavior, anorexia, and prominent bright-red cuticular patches, occasionally accompanied by melanized erosions. Prolonged anorexia and progressive melanization were associated with persistent mortality in the hatchery. Histopathological examination revealed severe muscle fiber degeneration, cuticular erosion, depletion of hepatopancreatic vacuoles, and gill lesions characterized by hemocyte infiltration and encapsulation. A dominant yellow-pigmented bacterium isolated on thiosulfate–citrate–bile salts–sucrose agar was molecularly identified as Vibrio harveyi strain AGK0045. Its pathogenic potential was further supported by a controlled 60-d experimental challenge in Pacific white shrimp, during which characteristic disease signs were reproduced. The challenge strain was subsequently re-isolated from affected shrimp and confirmed by molecular sequencing. Conclusions The findings provide strong evidence supporting the association of V. harveyi AGK0045 with the etiology of BRS in Pacific white shrimp broodstock. Although the observed prevalence suggests that the condition may be managed through appropriate screening and biosecurity measures, the findings emphasize the need for early diagnosis and further investigation of disease dynamics and potential risks to the sustainability of shrimp hatcheries in India.