Bolitas Syndrome in Penaeus vannamei Hatcheries in Latin America

In September 2023, several Penaeus vannamei hatcheries across Latin America experienced severe larval mortalities reaching up to 90% at the zoea 2 stage. Wet-mount observations identified spherical, lipid-like structures characteristic of Larval Bolitas Syndrome (LBS), alongside empty digestive tracts. Comprehensive PCR screening for over 20 known shrimp pathogens showed no viral causal agents and ruled out Acute Hepatopancreatic Necrosis Disease (AHPND). Microbiological assessments revealed that total heterotrophic bacterial counts were an order of magnitude higher, and presumptive Vibrio counts were almost two orders of magnitude higher in affected zoeas (reaching 10^6 CFU/g; 17% of total microflora) compared to healthy larvae (6%). Molecular and biochemical analyses identified multiple Vibrio species, predominantly Vibrio alginolyticus. Histopathological examination of affected zoeas demonstrated distinct epithelial cell shedding, hepatopancreatic necrosis, degraded peritrophic membranes, and heavy colonization by Gram-negative bacteria, in contrast to healthy larvae displaying intact gut structures with active microalgal feeding. These findings underscore the critical role of Vibrio dysbiosis in LBS outbreaks during early shrimp larviculture.