Effects of a plantmeal vs. fishmeal diet on intestinal integrity between two strains of rainbow trout (Oncorhynchus mykiss) reveal regional, strain, and diet differences

This study investigates the physiological differences in intestinal integrity between two strains of rainbow trout ( Oncorhynchus mykiss ), a commercial strain (CS) and a genetically selected strain (ARS- Sel ) developed for improved growth on plant-based diets, in response to differential dietary treatments. Fish were fed either a fishmeal (FM)- or a soybean-rich plantmeal (PM)-based diet for 19-weeks, after which intestinal integrity was evaluated across four intestinal regions using transepithelial electrical resistance (TEER) in Ussing chambers. This was in addition to assessing growth performance, distal intestinal histopathology, and gene expression of tight junctions and regulatory proteins. Interestingly, similar patterns of TEER profiles for all segments and treatment groups suggested conserved regional function, but diet and strain specific differences were observed. Specifically, the anterior proximal intestine exhibited a strain effect between the FM diets, where the lower TEER in the ARS- Sel FM group likely reflects a physiological adaptation associated with selection for PM-based growth. On the other hand, the mid-intestine TEER was significantly lower in the CS PM (strain effect), suggesting that the CS fish may be more susceptible to compromised integrity when fed the PM. In contrast, the distal intestine exhibited diet effects, where both strains had statistically lower TEER under the PM diets, consistent with diet-induced enteropathy linked to high-inclusion levels of soy. This was further corroborated via histopathology and gene expression analyses. Overall, these results show distinct dietary and genetic influences on intestinal barrier function in rainbow trout, strongly suggesting further studies correlating digestive physiology in response to plant-based feeds. • Differences in intestinal integrity influenced by genetics and diet in rainbow trout. • Integrity in proximal segments preserved in response to fishmeal and plantmeal diets. • Mid- and distal segments exhibit compromised barrier function to plantmeal diets. • Plantmeal diet significantly affects integrity in distal segment in both strains. • Underlying physiological mechanisms do not align with observed growth performances.