In vertebrates, taste provides critical information about the quality and nature of nutrients, leading to specific eating responses (consumption or avoidance), fundamental to their growth and survival. Taste perception is one of the first sensing system involved in oro-sensory detection of nutrients that play key role in the regulation of feeding behavior. Previous studies revealed that the concomitant replacement of traditional ingredients of aquafeed, fish meal and fish oil by plant ingredients (totally devoid of omega-3 long chain polyunsaturated fatty acid, ω-3 LC-PUFA) from first feeding of rainbow trout (RT, Oncorhynchus mykiss) led to a reduction of growth and survival rates (Lazzarotto et al., 2018), mainly related to altered feeding behavior. In fish, the impact of ω-3 LC-PUFA in the modulation of food detection and its involvement in the regulation of feeding behavior is largely unknown. In this study, we assessed the impact of feeding of alternative plant ingredient (without ω-3 LC-PUFA) vs commercial-like diet on the mechanism of food detection in the oro-sensory system in RT. After unique meal, we characterized by post prandial kinetics experiment (before meal, 20mns, 2 hours, 6 hours, 10 hours and 24 hours after meal) the expression pattern of appetite regulating neuropeptides in hypothalamus, free fatty acids receptor family (FFAR), the calcium signaling pathways and indolamine pathways in tongue. Overall findings show that RT displayed the fundamental mechanisms for oro-gustatory perception of nutrients related to different diet composition. The data obtained also indicated that taste receptors for fatty acids (such as the ffar receptor) and pathways involved in nutrients detection (such as calcium or monoaminergic pathways) are involved in the post-prandial regulation of food intake in fish, and their differential regulation according to the proposed diet could suggest a role in the regulation of appetite.