Abstract
Many kinds of fish are characterized by a limited efficiency to use carbohydrates. For this reason, raw fish and mixed feed containing a lot of fish meal have been used as feed for fish farming. However, continuing to use high-protein diets not only increases the cost of fish farming, but may also fuel animal protein shortages. Furthermore, carbohydrates are added to improve the texture of the feed and act as a binding agent and are usually contained at 20% in the feed. It makes sense, therefore, to find ways to make good use of carbohydrates rather than wasting them. The physiological mechanisms of glucose intolerance in fish are not yet well understood. Therefore, we investigated the glucose utilization of fish, omnivorous goldfish Carassius auratus and carnivorous rainbow trout Oncorhynchus mykiss. Furthermore, the effects of oral administration of wild plant-derived minerals and red ginseng on the glucose utilization in these fish muscle cells were investigated. As a result, we found the following. (1) An extremely high insulin resistance in fish muscle and the symptom was more pronounced in carnivorous rainbow trout. (2) Administration of wild plant-derived minerals promotes the translocation of the insulin-responsive glucose transporter GLUT4 to the cell surface of white muscle via activation of the PI3 kinase axis, whereas administration of red ginseng not only promotes GLUT4 transfer and translocation to the cell surface of white muscle via AMPK activation as well as promoting glucose uptake into muscle cells via a pathway separate from the insulin signaling system. (3) In fish, at least goldfish and rainbow trout, both PI3K/Akt and AMPK signaling cascades exist to promote glucose uptake into muscle cells, as in mammals.