Yellowtail (Seriola quinqueradiata ) is an important aquaculture species in Japan; it has low palatability for an alternative protein source of fishmeal. For sustainable aquaculture, increasing the feed intake of low- or non-fishmeal diets in yellowtail is necessary. Olfactory and gustatory senses are important in fish feeding; h owever, it remains unclear how each of these senses stimulates feed intake in yellowtail. Therefore , this study investigated the effects of amino acids on the feeding mechanisms of yellowtail.
Twelve L-amino acids (Ala, Pro, Ser, Asp, Tau, Thr, Gln, Met, Trp, Val, His, and Ile), exhibiting both strong or weak olfactory and gustatory stimulation, were selected for this study. Different amino acid solutions (10 mmol) were added to the rearing water of yellowtail, and the frequency of “search” and “b ite” instances were counted (Fig. 1) . The addition of strong odor-stimulati ng amino acid solutions resulted in significantly higher frequencies of “search” behavior than that seen with the vehicle. Compared to that seen with the vehicle, the “bite” frequency was significantly increased by the addition of Pro and Met. Pro was the most taste-stimulating amino acid, whereas Met exerted a very weak taste-stimulating effect. The mRNA response of neuropeptide Y (npy ), an orexigenic hormone in the olfactory bulb, telencephalon, hypothalamus, and cerebellum of the yellowtail, was measured after adding 10 mmol of amino acid solution to the rearing water. The addition of Ala, the strongest olfactory stimulator, significantly decreased npy expression in all brain regions. Fifteen minutes after adding an amino acid solution to the rearing tank, a commercial diet was fed until satiation and feed intake were measured. Compared to that seen with the vehicle, the addition of strong olfactory stimulants such as Ala, Ser, Met, and Gln significantly reduced feed intake (Fig. 2).
In conclusion, yellowtail recognizes amino acids as feed via olfaction and gustation, leading to feeding behavior and contributing to feed intake , primar ily by regulating npy expression in various regions of the brain apart from the hypothalamus.
This work was supported by Grant-in-Aid for JSPS Fellows Grant Number JP21J23499, JSPS KAKENHI Grant Number JP21H02286, and a JST Grant Number JPMJPF2117.