Unravelling the intricate language of fish guts: Impact of plant-based vs. plant-insect-poultry-based diets on intestinal pathways in European seabass

The long-term sustainability of aquaculture depends on finding economically viable and environmentally friendly feed ingredients to reduce the use of fishmeal and fish oil. An optimal strategy for the industry is not to identify substitutes or alternatives, but to find a combination of complementary raw materials that together meet the specific nutritional requirements for a given farmed fish species. The study aimed to examine the effects of different diets on the pyloric caeca and distal intestine of subadult European seabass (Dicentrarchus labrax) by applying transcriptomics and transmission electron microscopy. The study examined three dietary approaches: the classic fishmeal-based diet, a plant-based diet, and a plant-insect-poultry-based diet. The distal intestine was more sensitive to dietary changes than the pyloric caeca. The differentially expressed genes in both experimental diets were mainly involved in the digestion and absorption of proteins, fats, and vitamins. The overall transcriptomic changes were greater in the plant-based group than in the plant-insect-poultry-based group and included a greater number of overrepresented metabolic and signalling pathways. In contrast to the transcriptomic results, the ultrastructural findings showed decreased inflammation and/or evidence of tissue repair in the plant-based group, particularly in the pyloric caeca. Since the nutritional quality of all fish groups in this study was previously evaluated positively, the detected transcriptome-level changes can serve as evidence supporting the efficient nutrient utilisation and adaptability in European seabass. The study provides valuable insight into the potential benefits and implications of these dietary modifications on intestinal health and pathway regulation in European seabass. This can serve as a basis for further development of sustainable European seabass aquaculture practices and optimisation of diet formulations. •Novel dietary approaches: Plant-based diets with complementary non-fish ingredients.•Overall transcriptomic changes greater in the plant-based diet group.•Gut specialisation: Distal intestine showed stronger response than pyloric caeca.•Ultrastructural analysis: Reduced inflammation noted in the plant-based diet group.•Sustainable implication: Insights for optimising European seabass aquaculture diets.