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

Two experiments were conducted to examine whether a mixture of bacteria composed of Bacillus licheniformis, Bacillus subtilis and Bacillus pumilus has a beneficial impact on survival, growth, lysozyme activity and total immunoglobulins (Ig) in perch larvae. In experiment 1, control fish were compared with fish receiving bacteria (4.93 x 107 CFU L-1 day-1) through tank water or both through tank water and Artemia metanauplii enriched with two bacteria doses (2 x 1010 or 4 x 1010 CFU L-1). Treatments were performed in 40 L triplicate tanks of 200 fish [initial body weight (IBW)=2.3 mg] each, placed in separated recirculating water systems. Experiment 2 evaluated the combining effects of bacteria feeding and densities (10 vs. 20 fish L-1, IBW=9.5 mg). In both experiments, the bacteria added to live food or both live food and water induced higher growth rate at the highest dietary dose and this was associated with higher Ig levels on days 14 and 28. In experiment 2, higher survival was associated to lower type-2 cannibalism (ingestion of whole prey) at the two dietary bacteria doses, and such positive effect was observed for fish fed bacteria at high density. Bacteria administration through water had no effect on growth and survival. In conclusion, the results show that high dietary concentrations of the mixture of bacteria used have potential stimulating impact on growth, survival, lysozyme activity and total Ig. But, further investigations are needed to demonstrate the optimal doses for emphasizing immune defence status.