This study evaluated the effect of fermentation with Lactobacillus acidophilus on the biochemical and nutritional compositions of a plant-based diet and its effects on the productive performance and intestinal health of juvenile Nile tilapia (Oreochromis niloticus) reared in a biofloc technology (BFT) system. The in vitro kinetics of feed fermentation were studied to determine the L. acidophilus growth and acidification curve through counting the colony-forming units (CFUs) mL⁻¹ and measuring the pH. Physicochemical and bromatological analyses of the feed were also performed. Based on the microbial growth kinetics results, vegetable-based Nile tilapia feeds fermented for 6 (FPB6) and 18 (FPB18) h were evaluated for 60 days. Fermented diets were compared with a positive control diet containing fishmeal (CFM) and a negative control diet without animal protein (CPB). Fermentation with L. acidophilus increased lactic acid bacteria (LAB) count and the soluble protein concentration of the plant-based feed, as well as decreasing the pH (p < 0.05). FPB treatments improved fish survival compared with CPB (p < 0.05). Fermentation increased feed intake but worsened feed efficiency (p < 0.05). The use of fermented feeds increased the LAB count and reduced pathogenic bacteria both in the BFT system’s water and in the animals’ intestines (p < 0.05). Fermented plant-based feeds showed greater villi (FPB6; FPB18) and higher goblet cell (FPB6) counts relative to the non-fermented plant-based feed, which may indicate improved intestinal health. The results obtained in this study are promising and show the sustainable potential of using fermented plant-based feeds in fish feeding rather than animal protein and, in particular, fishmeal.

This study evaluated the effects of different total suspended solid (SST) levels (0, 250 and 350 mg L⁻¹) on the productive performance, intestinal condition and antioxidant enzyme activity of rainbow trout (Oncorhynchus mykiss) fry reared in a biofloc technology (BFT) system. The experimental design was completely randomized with three treatments and five replicates. A total of 225 rainbow trout fry (0.81 ± 0.06 g) were distributed into 15 tanks (70 L working volume) at a stocking density of 15 fish per tank. Tanks designated for the control treatment (clear water) were connected to a recirculating aquaculture system, whereas BFT treatments were maintained in independent units. Performance analyses were conducted and fish were sampled for intestinal histomorphometry, intestinal microbial counting and antioxidant enzymatic activity. Rearing rainbow trout fry in BFT systems with TSS levels up to 250 mg L⁻¹ proved feasible and preserved zootechnical performance, intestinal condition and antioxidant enzyme activity during the early stages of development. The higher TSS concentration negatively affected fish growth performance. However, increased colonization by lactic acid bacteria was observed, indicating that biofloc may serve as a source of probiotic bacteria. The BFT system is a viable alternative for rearing rainbow trout fry, enhancing biosecurity and reducing water consumption.

This study evaluated the effects of feed fermented with Lactobacillus acidophilus and Lacticaseibacillus rhamnosus on the growth performance and intestinal condition of the juvenile rainbow trout Oncorhynchus mykiss. 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.