A 60-day feeding trial was conducted to evaluate the effects of dietary Anabaena blue-green algae (ABGA) meal on the growth performance, digestibility, and physio-metabolic responses of Catla catla fingerlings (initial average weight 9.45 ± 0.15 g). Six iso-nitrogenous (30% crude protein) and iso-caloric (378.09 Kcal. digestible energy/100 g) diets were formulated: a control diet (A0, 0% ABGA) and five experimental diets with varying ABGA inclusion levels (A3: 3%, A6: 6%, A9: 9%, A12: 12%, A15: 15%). The results demonstrated that there were no significant differences (P > 0.05) in percentage weight gain (PWG), specific growth rate (SGR), protein efficiency ratio (PER), and feed conversion ratio (FCR) among the experimental groups. Additionally, dietary ABGA did not significantly affect (P > 0.05) body carcass composition among different groups. However, amylase activity significantly decreased (P < 0.05) in the A12 and A15 fed groups, whereas lipase and protease activities remained insignificant (P > 0.05) across all groups. Notably, oxidative stress responses (SOD; superoxide dismutase and CAT; catalase), carbohydrate metabolic enzymes (LDH; lactate dehydrogenase and MDH; malate dehydrogenase), and serum glucose levels increased significantly (P < 0.05) with higher ABGA inclusion. Conversely, serum albumin content significantly decreased (P < 0.05) in the ABGA-fed groups. There were no significant differences (P > 0.05) observed in serum total protein, albumin/globulin (A/G) ratio, aspartate aminotransferase (AST), and alanine aminotransferase (ALT) activities among the experimental groups. Hematological parameters revealed that RBC (red blood cell) count, hemoglobin (Hb) concentration, and packed cell volume (PCV) significantly decreased (P < 0.05), while WBC (white blood cell) count significantly (P < 0.05) increased with higher dietary ABGA inclusion. In conclusion, the inclusion of dietary ABGA up to 15% did not impair nutrient utilization and supported normal growth performance in C. catla fingerlings. However, higher inclusion levels may have a detrimental effect on their growth, nutrient utilization, and physio-metabolic responses.
