Abstract

The influence of two commercial probiotics on the growth, innate immune parameters and intestinal morphology of rainbow trout (Oncorhynchus mykiss) juveniles (initial weight: 16.4 ± 0.4 g) was evaluated. Two probiotic types: A, multi-species (Bacillus sp., Pedicoccus sp., Enterococcus sp., Lactobacillus sp.) and B, mono-species (Pediococcus acidilactici) were tested at two levels each (A1: 1.5 g kg−1, 8.6 × 105 CFU g−1; A2: 3 g kg−1, 1.6 × 106 CFU g−1; B1: 0.1 g kg−1, 2.6 × 104 CFU g−1; B2: 0.2 g kg−1, 7.2 × 104 CFU g−1) versus an unsupplemented diet (C). Diets were distributed to sextuplicate tanks, three times a day to visual satiation for 8 weeks. Growth performance and immune responses (plasma lysozyme, ACH50, peroxidase and head kidney respiratory burst) were determined at 4 and 8 weeks of feeding. Body composition and intestine morphology were determined at the end of the feeding trial.At 8 weeks, the lower dose of multi-species probiotic (A1) improved growth rate, while both probiotic types improved feed conversion rate compared to the control animals, at the lower dose of multi-species (A1) and at the higher dose of mono-species (B2) probiotics. Body composition did not vary between treatments. At 4 weeks, ACH50 activity was significantly higher in fish fed higher dose of B probiotic (B2, 123.7 ± 50.6 vs 44.1 ± 7.7 U.ml-1 in control). At 8 weeks, lysozyme activity was higher in fish fed A1 (13.1 ± 5.2 μg ml−1) diet compared to fish fed control diet (7.8 ± 1 μg ml−1). Plasma peroxidase and head-kidney respiratory burst did not differ among the dietary treatments. Villi length and integrity and goblet cell counting of a cross section of the anterior intestine were not significantly different between groups.Results suggest benefits in zootechnical performance and immune humoral responses using both probiotic types, in a dose dependent manner, without apparent alterations in intestinal morphology.

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