Tributyrin Supplementation in Rainbow Trout

In the experimental feeding trial, each tank was randomly assigned to one of the dietary treatments as follows: basal control diet (Cont), diet supplemented with a tributyrin product (TBT, supplied by Lucta S.A., Barcelona, Spain) at 0.1% (m/m) (TBT1), 0.2% (TBT2), and 0.4% (TBT4) (triplicate tanks per diet). This product consisted of 98% purity tributyrin (55%) and silica carrier (45%). A detailed description of the formulation of each diet can be found in Supplementary Table S1. Despite using 60% plant-based meals, it is worth noting that this was not a fishmeal-free diet, and 10% fishmeal was included. This formulation was developed to be nutritionally challenging but with a realistic application in the commercial context. Fish were hand-fed twice a day to apparent satiety at 9:00 h and 16:00 h during 50 days. Rainbow trout had an initial body weight (IBW) of 18.99 ± 0.19 g (mean ± SE) and a final body weight (FBW) of 63.23 ± 1.02 g at the end of the trial. No significant differences were found in the IBW (P = 0.478).