In the context of sustainable aquaculture development, it is crucial to reduce the use of traditional ingredients such as fish meal and fish oil. However, their total replacement with plant-based ingredients leads to a significant alteration in the survival and growth performance of rainbow trout, starting from the first meal and throughout their life cycle. Increasingly, studies are identifying altered feeding behavior as a hypothesis, although few mechanistic studies have confirmed this so far. While the removal of fish meal and fish oil results in the removal of omega-3 intake (DHA/EPA), few data exist regarding the impact of these nutrients on the feeding behavior of farmed fish. Yet, nutrient detection plays a crucial role in food selection, assessment, and ingestion in animals.
Therefore, understanding the mechanisms that regulate the feeding behavior of rainbow trout, such as the involvement of omega-3 fatty acids, is a prerequisite for acquiring crucial knowledge to develop new nutritional strategies aimed at improving the regulation of food intake throughout the rainbow trout’s life cycle.
We investigated the effect of a plant-based diet on the mechanisms of food detection in rainbow trout. For this purpose, two postprandial kinetic studies (fasted, 20 minutes, 2 hours, 6 hours, 10 hours, and 24 hours postprandial) following a single meal (in juvenile trout) or after 30 days of feeding (following the first meal) were conducted.
Our results demonstrat e that the nature of the diet (diet with fish meal and fish oil vs. plant-based) influences the expression of nutrient receptor genes, such as free fatty acid receptors, at the gustatory system level in trout, both following a single meal with a plant-based feed or after 30 days of feeding following the first meal. An alteration in serotonin regulation (a key neurotransmitter in taste information transmission and animal behavior ) induced by plant-based feeding, particularly in areas associated with decision-making and behavior control, is also observed. These results not only show a deregulation of the integrated feeding response by plant-based feeding but also highlight the remarkable sensitivity of nutrient detection mechanisms in rainbow trout to new food sources.
Finally, additional in vitro data on the affinity of fatty acids on sensory receptors demonstrate that gustatory receptors could play a crucial role in the fine distinction of foods with different levels of omega-3 in rainbow trout, revealing increased sensitivity to certain fatty acids.
Acknowledgements: This research was funded by the French National Research Agency (grant no. ANR-21-CE20-0009-01 “FEEDOMEGA”