Bacterial diseases have been reported to be the major limiting factor in shrimp production. The use of natural products such as antimicrobials has been reported as a solution to the problem. The crude extract of a red seaweedLaurencia snyderiae obtained from the Persian Gulf was evaluated for shrimp growth performance and to determinein vivo efficacy of this seaweed in the prevention of shrimp Vibriosis. The ethanol extract fromL. snyderiae (EELS) that was fed to theArtemia instar I for their enrichment was found to be non toxic to them. ShrimpLitopenaeus vannamei juveniles were fed with these enrichedArtemia at 0 mg mL-1 (Control group), 200 mg mL-1, 400 mg mL-1 and 600 mg mL-1 for 30 days. The results obtained showed a significant increase (p<0.05) in survival rate in treatment groups compared with that in the control group. Shrimps fed with enrichedArtemia showed a significant improvement in growth parameters when compared to those in the control group. When these juvenile shrimps were exposed toVibrio harveyi (after 30 days) they showed notably lower mortality than the control. These results indicate that EELS has a good potential in promoting growth and antibacterial activities againstV. harveyi that is useful in shrimp aquaculture.

Keywords: Red seaweed,Laurencia snyderiae, Litopenaeus vannamei, Vibrio harveyi