Sense of smell is mediated by diverses families of olfactory sensing receptors, conveying important dietary information, fundamental for growth and survival. In rainbow trout (RT, Oncorhynchus mykiss), the identification and regulation of their olfactory system remain poorly described. The aim of this study was to elucidate the implication of the sensory olfactory pathways in the regulation of feeding behaviour of carnivore RT fed from first feeding until 8 months with plant-based diet and to characterize their modulation before and after a meal. RT fed plant-based diet drastically altered growth performance by early affecting feed intake. Exhaustive examination of RT genome database identified 3 vomeronasal type 1 receptor-like (ORA), 10 vomeronasal type 2 receptor-like (OLFC) and 14 main olfactory receptor (MOR) encoded, all highly expressed in sensory organs, revealing their potential functionality. Gene expression after feeding revealed importance in olfactory sensing perception of some OLFC (olfcg6) and MOR (mor103, -107, -112, -113, -133) receptor family in RT. Conversely, ora1a seem involved in olfactory sensing perception for fish fed a commercial-like diet, ora5b, mor118, mor124 and olfch1 for fish fed plant-based diet. Results indicated an impact of the plant-based diet on the regulation of olfactory sensing pathways as well as its influence on monoaminergic neurotransmission in brain area related to olfactory-driven behaviors. Overall findings suggested that feeding behaviour are mediated through olfactory sensing detection and olfactory-driven behavior pathways in RT.