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Commercial Bacillus probiotic supplementation of rainbow trout (Oncorhynchys mykiss) and brown trout (Salmo trutta): growth, immune responses and intestinal morphology

Ramos, Maria Amélia, Gonçalves, José F M, Costas, Benjamín, Batista, Sónia, Lochmann, Rebecca, Pires, Maria A, Rema, Paulo, Ozório, Rodrigo O A
Aquaculture research 2017 v.48 no.5 pp. 2538-2549
Bacillus cereus, Bacillus subtilis, Oncorhynchus mykiss, Salmo trutta, body composition, complement, enterocytes, enzyme activity, experimental diets, growth performance, immune response, innate immunity, lysozyme, nutritional intervention, peroxidase, probiotics, soybean meal, trout, villi
Probiotic administration is associated with the enhancement of host resistance to environmental and nutritional stressors, improving survival and growth rates. This study was carried out to evaluate the effects of dietary supplementation of Bacillus subtilis and Bacillus cereus toyoi on growth performance, innate immune responses and gut morphology of two trout species feeding a commercial diet high in soybean meal. A commercial probiotic (4.2 × 10⁹ CFU g⁻¹ of additive) was supplemented to the experimental diets at 0% (control), 0.03% (P₁; 6 × 10³ CFU g⁻¹ of diet) or 0.06% (P₂; 1.5 × 10⁶ CFU g⁻¹ of diet) and fed to brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) for 9 and 20 weeks respectively. Rainbow trout showed significantly better growth performance than brown trout, regardless of the dietary treatment. No effect of dietary probiotic supplementation was detected on growth performance, body composition or innate immune parameters (plasma lysozyme, alternative complement and peroxidase activities). In both species, after 9 weeks, intestinal lamina propria and submucosa were widened, with increased presence of inflammatory cells, significantly higher in groups fed probiotics. This inflammatory process, with villi and enterocytes noticeably damaged compared with the control group, was more pronounced in brown trout. Under the current trial conditions, the B. subtilis + B. cereus toyoi had no positive impact in either trout species, on the contrary a harmful effect was observed.