Increased leptin may be involved in the short life span of ayu (Plecoglossus altivelis).

It is well known that ayu (Plecoglossus altivelis) die after spawning and have a life span of only 1 year. The determinants for such a short life span are probably connected with spawning and related changes in hormonal homeostases. One of these changes is that the ayu's feeding activity decreases both during and after spawning. We investigated the relationships among leptin, one of the regulators of food intake, and two other major hormones, 17 beta-estradiol and prolactin (PRL). Ir-leptin levels were significantly higher during spawning, and were associated with a decrease in appetite. Ir-leptin levels were also synchronized with levels of 17 beta-estradiol and PRL-like protein. Therefore, one possible explanation for the decrease in appetite during ayu spawning is that the elevation of 17 beta-estradiol homeostasis induced the secretion of Ir-leptin. The inability to decrease leptin to the basal levels because of high estrogen after spawning could be in part responsible for the short life span of ayu.