In fish, appetite control is closely related to feed intake. Feed intake is an essential factor in fish production, and it is directly related to fish growth and improves aquaculture production. Ghrelin, a gene linked to appetite regulation, increases the expression of ghrelin in mammals and fish as the fasting time increases, thereby promoting the individual’s appetite. Ghrelin binds to the ghrelin receptor in the pituitary gland to stimulate the secretion of growth hormone and acts on the nervous system to promote food intake. Since appetite control of starry flounder is also closely related to feed intake, basic research on appetite regulation is essential to improve the production of starry flounder.
In this study, we confirmed ghrelin expression and growth in long-term fasting of the starry flounder, and the endocrine changes in ghrelin according to the long-term fasting pattern were approved. In addition, LEAP2, which has been reported as an antagonist of ghrelin, was used as a tool to identify the endocrine pattern of ghrelin. The long-term fasting patterns of the experiments in this study were group A (regular feeding twice daily for eight weeks), group B (2-4 weeks, fed for 6-8 weeks, fasting the rest), and group C (feeding for 4-8 weeks, fasting for the rest of the period) and group D (fasting for 0-8 weeks) were all different.
Group C showed the highest daily growth rate, followed by group B and group A the lowest. According to long-term fasting and refeeding, the expression of ghrelin in the starry flounder increased slightly during the first two weeks of fasting in group B, decreased after feeding, and increased more than seven times during the 4-6 weeks fasting period. Similarly, in group C, the expression level of ghrelin continued to grow during the fasting period. Starry flounder growth hormone, according to long-term fasting and refeeding, tended to increase at four weeks after the fasting period in group B, rose at two weeks and 5-6 weeks in group C, and increased at two weeks in group D, these showed a tendency to increase at 4-5 weeks. According to the results of this study, long-term fasting in starry flounder increases the expression of ghrelin and leads to an increase in the growth hormone and acyl ghrelin. These results will be used basic data to help us understand the physiological role of ghrelin in the endocrine system of fish.