Las Bolitas Syndrome in Penaeus vannamei Hatcheries in Latin America

In September 2023, several hatcheries in Latin America experienced up to 90% mortality in zoea stage 2 of Penaeus vannamei exhibiting clinical signs of "las bolitas syndrome" (LBS). This study evaluated healthy and diseased zoea via microbiology, PCR, and histopathology. Microbiological analyses showed total heterotrophic bacteria (1.28 × 10^7 CFU/g) and presumptive Vibrio counts (2.22 × 10^6 CFU/g) were up to two orders of magnitude higher in diseased larvae compared to healthy controls (6.85 × 10^4 CFU/g). PCR screening for over 20 known shrimp pathogens was negative for AHPND and major viruses, but positive for Vibrio spp. and Rickettsia-like bacteria in diseased batches. Fourteen isolated bacterial strains were identified as Vibrio spp. by PCR, including strains biochemically identified as Vibrio alginolyticus and V. fluvialis. Histopathological examination revealed marked epithelial cell detachment, hepatopancreatic necrosis, presence of Gram-negative bacteria, and compromised peritrophic membranes in affected larvae. These findings clarify the pathology of bolitas syndrome in P. vannamei hatcheries.