en aquaculture aquaculture پژوهشي Orginal research papers Probiotics can improve growth, survival and resistance to pathogenic organisms of the cultivated species in aquaculture systems with water recirculation. However, their possible benefits on biofloc systems have been less studied. In this study, the benefits of <em>Bacillus amyloliquefaciens</em> bacterium, on a biofloc culture of <em>Litopenaeus vannamei</em> were evaluated. <em>B. amyloliquefaciens</em> was applied as dissolved in water. To our knowledge, no previous assays on biofloc systems have been published, and on recirculation systems it has only been tested mixed with feed. The objective of the present study was to evaluate the effect of <em>B. amyloliquefaciens</em> on water quality, growth parameters and the immune system of shrimp. Three concentrations of probiotic were tested in triplicate (9.48 &times; 10⁴, 1.90 &times; 10⁵, and 3.79 &times; 10⁵cfu ml^-1) and were compared with the control (without probiotics). Water quality parameters such as nutrients and suspended solids were monitored. In <em>L. vannamei</em>, growth, survival and their immune system parameters (total protein concentration, cell number with apoptosis and percentage of granular and hyaline hemocytes) were studied. The results showed that the application of <em>B. amyloliquefaciens</em> did not produce significant differences in water quality or shrimp growth. However, it showed significant improvements in the immune system. As compared with the control treatment, an increase in the total protein concentration and granular hemocytes, and a decrease in the cell number with apoptosis in the hempolymph were observed. Thus, we can conclude that <em>B. amyloliquefaciens</em> provides greater resistance to shrimp against the attack of pathogens in biofloc systems. Growth parameters, Immunological parameters, Water quality, White shrimp 904 920 http://jifro.ir/browse.php?a_code=A-10-2866-1&slc_lang=en&sid=1 F. Llario ferllase@upv.es 100319475328460033954 100319475328460033954 Yes Insitut d’Investigació per a la Gestió Integrada de Zones Costaners (IGIC). Universitat Politècnica de València (UPV). L.A. Romano luisalbertoromano0@gmail.com 100319475328460033955 100319475328460033955 No Estação Marinha de Aquacultura, Instituto de Oceanografia, Universidade Federal do Rio Grande (FURG). M. Rodilla mrodilla@hma.upv.es 100319475328460033956 100319475328460033956 No Insitut d’Investigació per a la Gestió Integrada de Zones Costaners (IGIC). Universitat Politècnica de València (UPV). M.T. Sebastiá-Frasquet mtsebastia@hma.upv.es 100319475328460033957 100319475328460033957 No Insitut d’Investigació per a la Gestió Integrada de Zones Costaners (IGIC). Universitat Politècnica de València (UPV). L.H. Poersch lpoersch@mikrus.com.br 100319475328460033958 100319475328460033958 No Estação Marinha de Aquacultura, Instituto de Oceanografia, Universidade Federal do Rio Grande (FURG).