Agricultural Research,Education and Extension Organization Iranian Journal of Fisheries Sciences 1562-2916 25 4 2026 07 01 A comparison of growth performance and digestive enzyme responses in common carp (Cyprinus carpio) across different culture phases 675 690 135849 10.22092/ijfs.2026.135849 EN T. Mohammadiam Department of Livestock, Poultry and Aquatic animal Health, Shahid Chamran University of Ahvaz, Ahvaz, Iran A. Valipour Department of Mechanical Engineering, Shahid Chamran University of Ahvaz M.R. Mokhtari Faculty of Veterinary Medicine, Shahid Chamran University of Ahvaz, Ahvaz, Iran M. Mesbah Department of Livestock, Poultry and Aquatic animal Health, Shahid Chamran University of Ahvaz, Ahvaz, Iran M. Alishahi Department of Livestock, Poultry and Aquatic animal Health, Shahid Chamran University of Ahvaz, Ahvaz, Iran B. Dixson Department of Biology, University of Waterloo S. Samiee Department of Chemistry, Shahid Chamran University of Ahvaz Journal Article 2026 07 20 This study evaluated the effects of biofloc technology (BFT) on growth performance and digestive enzyme activity in common carp (<em>Cyprinus carpio</em>) across two consecutive culture phases: a 90-day nursery phase (250-L tanks) followed by a 120-day grow-out phase (100 m³ ponds). Three treatments were compared: a semi-closed recirculating system (control), a biofloc-recirculating system with indigenous <em>Bacillus</em> spp. (BFT+P), and a biofloc system without probiotics (BFT). Key growth parameters (<em>i.e. </em>specific growth rate, relative growth rate, feed conversion ratio (FCR), protein efficiency ratio, and daily weight gain) and intestinal digestive enzymes (<em>i.e. </em>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±0.10) versus control (1.36±0.20). Digestive enzyme activities were significantly higher in biofloc treatments (<em>p</em><0.05), with total protease peaking at 215.53±4.31 U mg⁻¹ 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±123 kg), and the lowest FCR (1.27±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. https://jifro.areeo.ac.ir/article_135849_ffd14bf3370f4e3f9b5131bda65db93d.pdf