en aquaculture aquaculture پژوهشي Orginal research papers <span lang="TR" style="font-size:11.0pt"><span calibri="" style="font-family:"><span style="color:black">The aim of this study was to investigate the effects of dietary supplementation of a commercial probiotic containing <i>Bacillus subtilis, Lactobacillus acidophilus</i>, <i>L. delbrueckii</i>, <i>L. rhamnosus</i>, and <i>L. plantarum</i> on growth performance, hematological and immunological parameters of bester fingerlings. Two-hundred and forty fingerlings (10&plusmn;0.9 g) were randomly distributed into 12 fiberglass tanks. The experimental diets were formulated using 0 (control), 100 (T100), 200 (T200), and 300 (T300) mg/kg of the probiotic. The fish were fed at 3% of body weight for 8 weeks. The result revealed that dietary probiotics increased final weight, condition factor, daily growth rate, specific growth rate, and body weight increase (<i>p</i>>0.05). Also, we observed a significant increase in feed efficiency ratio and protein efficiency ratio for fish fed with T300 compared to T200 (<i>p</i><0.05). Hematological parameters were not influenced by dietary probiotic levels (<i>p</i>>0.05). There were no significant differences in total immunoglobulin (<i>p</i>>0.05), while alternative complement activity was significantly enhanced by the inclusion of probiotics in diets (<i>p</i><0.05). The present study showed that feed efficiency, protein efficiency, and immunological parameters of bester fingerling have been improved by adding the commercial probiotic at 200 mg/kg.</span></span></span> Probiotic, Bester, Growth, Hematological parameters, Immunological Parameters 293 306 http://jifro.ir/browse.php?a_code=A-10-4609-1&slc_lang=en&sid=1 A. Hossienpour Zelaty ahpour.z@gmail.com 100319475328460051318 100319475328460051318 No International Caspian Sturgeon Research Institute, Agricultural Research, Education and Extension Organization (AREEO). Rasht. PO Box: 3464-41635 M.H. Seyed Hassani mirhamedhassani@yahoo.com 100319475328460051319 100319475328460051319 Yes International Caspian Sturgeon Research Institute, Agricultural Research, Education and Extension Organization (AREEO). Rasht. PO Box: 3464-41635 T. Sohrabi t.sohrabi@areeo.ac.ir 100319475328460051320 100319475328460051320 No International Caspian Sturgeon Research Institute, Agricultural Research, Education and Extension Organization (AREEO). Rasht. PO Box: 3464-41635 F. Bagherzadeh Lakani f.bagherzade@areeo.ac.ir 100319475328460051321 100319475328460051321 No International Caspian Sturgeon Research Institute, Agricultural Research, Education and Extension Organization (AREEO). Rasht. PO Box: 3464-41635 M. Mohseni 100319475328460051322 100319475328460051322 No International Sturgeon Research Institute, Iranian Fisheries Science Research Institute (IFSRI), Agricultural Research, Education and Extension Organization (AREEO), Rasht, Iran Z. Pajand sh.mirnabi@gmail.com 100319475328460051323 100319475328460051323 No International Sturgeon Research Institute, Iranian Fisheries Science Research Institute (IFSRI), Agricultural Research, Education and Extension Organization (AREEO), Rasht, Iran