The gut mucosal barrier of zebrafish (Danio rerio) responds to the time-restricted delivery of Lobosphaera incisa-enriched diets

Recent studies in mammalian models revealed compelling evidence that along with the intrinsic characteristics of diets, the time of their delivery could have a profound impact on their benefits. In this study, we explored a time-dependent modulation of the gut mucosal barrier by delivering diets enriched with the green microalga (Lobosphaera incisa) either in a time-restricted regime or randomly to zebrafish (Danio rerio). The basal diet was enriched with microalgal biomass through two inclusion levels (i.e., 10% and 15% w/w), and the feeding trial lasted for six weeks. The control group was fed with the basal diet. After collection of tissue samples at week 6, the remaining fish were challenged by intraperitoneal injection of Streptococcus inaie. A histological analysis of the gut structure revealed that the fish that received the microalgae randomly exhibited shorter villi length. Genes coding for immunity were modulated in the gut by dietary treatments. Notably, the transcript levels of lysozyme, β-defensin and hepcidin were significantly higher in the group subjected to the time-restricted feeding regime. Dietary microalgae affected the fatty acid content in the gut, particularly the level of arachidonic acid (ARA), and the time-restricted feeding influenced its accumulation. Groups that received diets enriched with 15% microalgae, regardless of the feeding strategy, displayed a significantly higher resistance to S. inaie 16 days post-infection, though differences between the delivery strategies were pronounced during the early stage of infection. In conclusion, the dietary inclusion of L. incisa modulated some of the features of the gut mucosal barrier of zebrafish, and the time of delivery appeared to have a considerable influence on immunomodulatory functions.