fa aquaculture aquaculture پژوهشي Orginal research papers <p>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 seaweed <em>Laurencia snyderiae</em> obtained from the Persian Gulf was evaluated for shrimp growth performance and to determine <em>in vivo</em> efficacy of this seaweed in the prevention of shrimp Vibriosis. The ethanol extract from <em>L. snyderiae</em> (EELS) that was fed to the <em>Artemia</em> instar I for their enrichment was found to be non toxic to them. Shrimp <em>Litopenaeus vannamei</em> juveniles were fed with these enriched <em>Artemia</em> 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 (<em>p</em><0.05) in survival rate in treatment groups compared with that in the control group. Shrimps fed with enriched <em>Artemia</em> showed a significant improvement in growth parameters when compared to those in the control group. When these juvenile shrimps were exposed to <em>Vibrio harveyi</em> (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 against <em>V. harveyi</em> that is useful in shrimp aquaculture.</p> <p></p> Red seaweed, Laurencia snyderiae, Litopenaeus vannamei, Vibrio harveyi 210 221 http://jifro.ir/browse.php?a_code=A-10-600-65&slc_lang=fa&sid=1 A. Dashtiannasb adashtiannasab@gmail.com 100319475328460020055 100319475328460020055 Yes V. Yeganeh 100319475328460020056 100319475328460020056 No