Olfaction and gustatory senses promote feeding through different pathways in yellowtail, Seriola quinqueradiata

For sustainable aquaculture, the replacement of dietary fishmeal with plant protein is becoming more common because fishmeal resources are limited. However, in the case of carnivorous fish such as yellowtail (Seriola quinqueradiata), reducing the dietary fishmeal level often causes low feed intake. Improving feed intake is important in the use of a non- and low-fishmeal diet. However, little is known about the mechanisms that regulate feeding in yellowtail. The relationship between appetite, feeding behaviour, and food intake needs to be examined to elucidate the mechanisms of feeding regulation. The senses of smell (olfaction) and taste (gustation) are important for feeding in fish. However, it is unclear how each of these senses stimulates feeding behaviour, appetite, and feed intake. In this study, the effects of olfactory and gustatory stimuli on feeding behaviour, brain expression of neuropeptide Y (NPY), and feed intake in yellowtail were investigated using a strong olfactory stimulant (alanine, Ala) and a strong gustatory stimulant (proline, Pro). By using observation tanks, feeding behaviour was divided into ‘search’ and ‘bite’. Ala promoted ‘search’ feeding behaviour and significantly decreased npy mRNA expression in the olfactory bulb and telencephalon as the olfactory centre and hypothalamus as the appetite centre. No increment in feed intake was found in the Ala-supplemented diets compared to the control diet. Meanwhile, Pro increased npy mRNA expression in the gustatory centre (cerebellum), promoted ‘bite’ feeding behaviour, and increased feed intake. Odour stimulation promoted ‘search’ through npy mRNA expression but was not reflected in feed intake. Taste stimulation promoted ‘bite’ through npy mRNA expression, which increased feed intake. Thus, olfactory and gustatory senses may promote feeding through different pathways in the yellowtail. These results will contribute to increasing the feeding amount of non- and low-fishmeal diet in the feed of yellowtail towards sustainable aquaculture.