Effects of probiotic bacteria on growth parameters and immune defence in Eurasian perch Perca fluviatilis L. larvae under intensive culture conditions

This study evaluated the efficacy of a commercial Bacillus probiotic mixture (Bacillus licheniformis, Bacillus subtilis, and Bacillus pumilus) on the zootechnical performance and immune response of Eurasian perch (Perca fluviatilis) larvae and postlarvae. In two 28-day trials, probiotics were administered via tank water (4.93 × 10^7 CFU/L/day), live food (Artemia metanauplii enriched with 2 × 10^10 or 4 × 10^10 CFU/L), or a combination of both across different stocking densities (10 vs. 20 fish/L). Delivering the highest probiotic dose (4 × 10^10 CFU/L) via live food significantly enhanced specific growth rate (up to 20.3% per day) and reduced final weight heterogeneity compared to control groups. In postlarvae, dietary probiotic delivery increased survival by 17% to 20% by mitigating type-2 cannibalism (whole-prey ingestion), even at higher stocking densities. Immunological assays revealed that total immunoglobulin levels increased significantly (by up to 191% over controls) by day 28 in groups fed probiotic-enriched Artemia, whereas lysozyme activity showed moderate or inconsistent stimulation. Probiotics delivered solely through rearing water yielded no significant benefits on growth or survival. Overall, dietary administration of Bacillus probiotics via live prey improves growth uniformity, reduces cannibalistic mortality, and stimulates humoral immune parameters in intensively reared perch.