Time-course of mRNA abundance of appetite-regulatory genes in the brain of rainbow trout fed a plant-based diet from the first feeding

The early developmental stages of fish are critical for improving feeding strategies and growth performance. Understanding feeding-regulatory mechanisms from the earliest stages of development is crucial, especially in the context of aquaculture, where early nutrition has a significant impact on feeding behaviour, growth and survival. This is particularly relevant in carnivorous species, such as rainbow trout (Oncorhynchus mykiss), where the complete replacement of fishmeal and fish oil with plant-based ingredients has negative effects on growth performance and early stage survival. This study investigates the time-course of mRNA abundance of genes encoding key appetite-regulatory neuropeptides and integrative signalling pathways from first feeding to 100 days post-feeding with either a commercial-like diet containing fishmeal and fish oil or a plant-based diet devoid of these marine-derived ingredients. Results showed that an initial diet based on plants does not notably affect the levels of mRNA for appetite-regulating neuropeptides in the brain of rainbow trout alevins. However, the plant-based diet induced slightly distinct patterns in gene mRNA abundance after the first meal, which may underpin reduced feed intake and growth performance. Some key appetite-regulatory neuropeptides, such as neuropeptide Y (npy) and cocaine- and amphetamine-regulated transcript (cartpt), exhibited progressive higher levels in the brain over time, while agouti-related protein 1 (agrp1) and pro-opiomelanocortin a1 (pomca1) levels decreased following initial feeding. Moreover, the expression of key integrative signalling components, including AMP-activated kinase α2 (pkraa2), mechanistic target of rapamycin (mtor), cAMP response-element binding protein 1 (creb1), and forkhead box O1 (foxo1), increased throughout growth, but their abundance was modulated differently by the dietary treatments. This study underscores the importance of understanding neuroendocrine responses to dietary formulations for optimizing aquafeeds and enhancing sustainability in aquaculture.