Evaluation of marine macro alga, Ulva fasciata against bio-luminescent causing Vibrio harveyi during Penaeus monodon larviculture

Vibrio harveyi is one of the major disease causing bacterium in shrimp larviculture and grow-out practices. V. harveyi produces many virulence cum pathogenic factors. Application of antibiotics against luminescence causes development of antibiotic resistance among V. harveyi. Therefore, it is obligatory to develop bio-inhibitory agents as substitute in lieu of antibiotics. Under this study, Ulva fasciata was collected and extracted for crude compounds, 300 µg extract showed 12.3 mm of bio-inhibition against V. harveyi through “agar well diffusion assay”. Further, U. fasciata extract at 300 µg/ml was treated against V. harveyi in LB broth and showed reductions on phospholipase and proteolysis. Production of bio-luminescence was reduced to 7.3, 7.7, 13.0, 17.0 counts per second (CPS) and growth also reduced to 24.91%. Further, U. fasciata extract at 200 mg/ml was tested against V. harveyi during Penaeus monodon larviculture and showed 32.40% reduction in the cumulative percentage mortality on postlarvae due to V. harveyi. Chemical constituents of U. fasciata was characterized by FTIR and GCMS. GC-MS analysis, reported to contain organic compounds such as Bis(2-ethylhexyl) phthalate was highest (88.42%), followed by 1,2- benzenedicarboxylic acid- butyl (2.47%). Therefore, it was concluded that U. fasciata may be a better bio-inhibitory agent against V. harveyi in shrimp larviculture.   Key words: Ulva fasciata extracts, antagonism, virulence factors, Vibrio harveyi, challenging shrimp postlarvae, cumulative mortality reduction.