Essential oils promote the growth performance of grass carp, Chinese soft-shelled turtles, and zebrafish

Essential oils have been increasingly used as feed additives or preservatives due to their safety and antibacterial activity. However, few studies have examined the effects of combined essential oils on growth performance of aquatic species and the underlying mechanisms. In this study, we found that the combined essential oils, cinnamaldehyde, thymol, carvacrol, and monolaurin, in a certain ratio, promoted the body length and weight significantly in grass carp (Ctenopharyngodon idella), Chinese soft-shelled turtles (Trionyx sinensis), and zebrafish. Mechanistically, the combined essential oils significantly promoted the up-regulation of growth hormone (GH) and insulin-like growth factor (IGF), enhancing the expression of genes involved in insulin-like growth factor I binding, hormone biosynthesis, histidine metabolic process, nutrient reservoir activity, lipid transporter activity, and carbon metabolism. These changes, generally, promoted the expression of the subsequent signaling such as JAK/STAT, PI3K/AKT, and MAPK/ERK significantly in the brain, liver, and muscle, which might jointly contribute to the increased growth performance in grass carp, Chinese soft-shelled turtles, and zebrafish. This study for the first time demonstrates that the four essential oil components, cinnamaldehyde, thymol, carvacrol, and monolaurin, combined in a certain ratio, promote GH-IGF axis and the subsequent JAK/STAT, PI3K/AKT, and MAPK/ERK signaling, thereby enhancing the growth in grass carp, Chinese soft-shelled turtles, and zebrafish generally. This study reveals the potential of combined essential oil in promoting the growth of aquatic species.