Evaluation of Ulva ohnoi as functional dietary ingredient in juvenile Senegalese sole (Solea senegalensis): Effects on the structure and functionality of the intestinal mucosa

This study evaluates the effects of the macroalgae Ulva ohnoi on growth and intestinal functionality and integrity of Solea senegalensis juveniles in a 90-day feeding trial. Ulva diet (U-5) included 5% dry U. ohnoi biomass, whereas an algae-free diet was used as control. After being fed for 45 and 90 days, fish body weight was recorded for growth evaluation, and biological samples were taken. The inclusion of U. ohnoi (5%) significantly affected growth performance of sole juveniles, given that after being fed for 45 and 90 days fish showed lower body weight, specific growth and weight gain rates than fish fed with the control diet. Compared to fish fed with control diet, protease activities measured in the pancreatic secretion was also reduced when Ulva was included in the diet, but these fish also showed increased alkaline phosphatase activity in their intestinal mucosa. Quantitative PCR revealed changes in the relative expression of a set of genes coding for enzymes involved in lipid absorption and metabolism, several digestive enzymes, as well as for some stress response indicators. Electron microscopy revealed a lack of damage in the intestinal mucosa, as well as significantly increased mucosal absorptive surface in those fish fed with Ulva-supplemented diet for 45 days, compared to control fish. The results suggest that U. ohnoi at low inclusion level could protect the intestinal epithelium of fish, but a relatively short administration period is recommended with the aim of avoiding negative effects on Senegalese sole growth and proteolytic digestive enzyme activities. [Display omitted] •The potential of Ulva ohnoi as functional additive for Solea senegalensis was evaluated.•Fish growth and pancreatic protease activity were reduced by U. ohnoi.•U. ohnoi improved the mucosal intestinal epithelium of Senegalese sole juveniles.•Diets including U. ohnoi modulated transcription of intestinal protein and lipid metabolism-related genes.