The LPS derived from the cell walls of the Gram-negative bacteria Pantoea agglomerans stimulates growth and immune status of rainbow trout (Oncorhynchus mykiss) juveniles

• Dietary LPS from Pantoea agglomerans promotes growth performance in trout.
• Dietary LPS from Pantoea agglomerans enhances the immune status of trout.
• Dietary LPS from Pantoea agglomerans enhanced the density of intestinal goblet cells.
• Dietary LPS from Pantoea agglomerans can be used as fish immunostimulant.

The effects of oral administration of LPS derived from the cell walls of Pantoea agglomerans (LPSp) were tested in rainbow trout fry (10 and 20 μg LPSp kg BW− 1 day− 1) considering their general condition, growth performance, body proximate composition, digestive enzyme activities, histological organization of the intestinal mucosa (number of goblet cells and villi height) and analysis of immunological blood parameters related to the non-specific immune response (hemolytic complement, lysozyme, bacteriolytic activity and respiratory burst). Trout were stocked in a recirculation system and fed three diets: a commercial trout feed (Aller Futura, ALLER AQUA) without the immunostimulant; LPSp, and the same diet in which the top coating the pellets of the control diet with the lyophilized powder of IP-PA1 dissolved in 2% fish oil (final concentrations were 0.06 and 0.12 g LPSp kg− 1 in order to achieve a feed dosage of 10 and 20 μg LPSp kg BW− 1 day− 1, respectively). Each dietary treatment was tested in triplicate and the trial lasted for 93 days. Diets containing LPSp promoted growth; the final mean body weight and standard length in animals fed the LPSp at 20 μg kg BW− 1 day− 1 were 17.4 and 6.4% higher than in the control group (P < 0.05). In addition, the oral administration of LPSp enhanced the density of intestinal goblet cells (P < 0.05) suggesting an enhancement of the intestinal innate immune function. These results were supported by the enhancement of the blood non-specific immune parameters (lysozyme, bactericidal activity and the levels of complement in serum, and respiratory burst from hemocytes) in fish fed 20 μg LPSp kg BW− 1 day− 1. These results may be of practical significance for fish farmers, since the administration of LPSp at 20 μg kg BW− 1 day− 1 might not only prevent disease in aquaculture systems, but also improve at the same time their growth performance and efficiency of the rearing process.