Gustavo Alberto Arbeláez Rojas, Nataly Neves Oliveira dos Santos, Larissa Stockhausen, Bia Pacheco Kozikowski, Mariana Bender, Fernanda Regina Delzivo, Luiz Augusto Cipriani, Éverton Skoronski, Pedro Toledo, German Merino Araneda, Thiago El Hadi Perez Fabregat
. Three fermentation times (3, 6, and 9 h) were compared against a non-fermented control diet. The experimental design followed a randomized block scheme, with four treatments and four replicates. Juvenile rainbow trout (22.2 ± 0.9 g) were distributed among 16 tanks (500 L) connected to a recirculation system at a density of 15 fish per tank. A commercial diet (45% crude protein) was fermented through solid-state fermentation. After 60 days, growth performance and intestinal condition were assessed. The microbial fermentation of extruded commercial feeds was efficient, increasing the lactic acid bacteria count and reducing pH within 6 h. Feeding fermented feeds reduced feed intake without affecting fish growth performance. Feed fermented for 3 and 6 h improved feed efficiency, and evidence of enhanced nitrogen utilization was observed. In addition, feed fermented for 6 h increased intestinal colonization by lactic acid bacteria and enhanced intestinal lipase activity. Feed fermented for 9 h showed evidence of improved intestinal condition. Overall, this study indicates that feed fermentation improves feed efficiency and intestinal condition in rainbow trout.