en aquaculture aquaculture پژوهشي Orginal research papers <span lang="TR" style="font-size:11.0pt"><span style="font-family:&quot;Calibri&quot;,sans-serif"><span style="color:black">This study evaluated the effects of biofloc technology (BFT) on growth performance and digestive enzyme activity in common carp (<i>Cyprinus carpio</i>) across two consecutive culture phases: a 90-day nursery phase (250-L tanks) followed by a 120-day grow-out phase (100 m&sup3; ponds). Three treatments were compared: a semi-closed recirculating system (control), a biofloc-recirculating system with indigenous <i>Bacillus</i> spp. (BFT+P), and a biofloc system without probiotics (BFT). Key growth parameters (<i>i.e. </i>specific growth rate, relative growth rate, feed conversion ratio (FCR), protein efficiency ratio, and daily weight gain) and intestinal digestive enzymes (<i>i.e. </i>trypsin, chymotrypsin, amylase, lipase, total protease, and alkaline phosphatase) were monitored. Results showed that BFT+P significantly improved growth and feed utilization. By day 90, FCR was lowest in BFT+P (1.10&plusmn;0.10) versus control (1.36&plusmn;0.20). Digestive enzyme activities were significantly higher in biofloc treatments (<i>p</i><0.05), with total protease peaking at 215.53&plusmn;4.31 U mg</span></span></span><span lang="TR" style="font-size:11.0pt"><span style="font-family:&quot;Cambria Math&quot;,serif"><span style="color:black">⁻</span></span></span><span lang="TR" style="font-size:11.0pt"><span style="font-family:&quot;Calibri&quot;,sans-serif"><span style="color:black">&sup1; in BFT+P at day 90. During the grow-out phase, BFT+P yielded the highest final average weight (1.4 kg), the highest harvested biomass (1228&plusmn;123 kg), and the lowest FCR (1.27&plusmn;0.24). Survival rate remained 100% across all treatments. Enzyme activities increased time-dependently under biofloc conditions, with the most stable and elevated responses in BFT+P. In conclusion, biofloc system, particularly when combined with indigenous probiotic supplementation, enhances digestive physiology and growth performance of common carp throughout sequential culture phases. These findings offer practical strategies for improving intensive carp aquaculture efficiency.</span></span></span> Biofloc technology, Common carp, Growth, Feed conversion ratio, Digestive enzymes, Recirculating aquaculture system, Culture phase 675 690 http://jifro.ir/browse.php?a_code=A-10-2127-4&slc_lang=en&sid=1 T. Mohammadian tak.mohammadian@gmail.com 100319475328460059230 100319475328460059230 Yes Department of Livestock, Poultry and Aquatic animal Health, Shahid Chamran University of Ahvaz A. valipour a.valipour@scu.ac.ir 100319475328460059231 100319475328460059231 No Department of Mechanical Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran M.R. Mokhtari MohammadRezaMokhtari@scu.ac.ir 100319475328460059232 100319475328460059232 No Faculty of Veterinary Medicine, Shahid Chamran University of Ahvaz, Ahvaz, Iran M. Mesbah MehrzadMesbah@scu.ac.ir 100319475328460059233 100319475328460059233 No Department of Livestock, Poultry and Aquatic animal Health, Shahid Chamran University of Ahvaz, Ahvaz, Iran M. Alishahi Alishahi@scu.ac.ir 100319475328460059234 100319475328460059234 No Department of Livestock, Poultry and Aquatic animal Health, Shahid Chamran University of Ahvaz, Ahvaz, Iran B. Dixson BrianDixson@yahoo.com 100319475328460059235 100319475328460059235 No Department of Biology, University of Waterloo, Ontario, Canada S. Samiee SepidehSamiee@scu.ac.ir 100319475328460059236 100319475328460059236 No Department of Chemistry, Shahid Chamran University of Ahvaz, Ahvaz, Iran