Studying the contribution of two types of landlocked Ayu fish in Lake Biwa to the next generation using nitrogen-stable isotope ratio analysis

Contribution of amphidromous (Ooayu) and lake types (Koayu) of the landlocked Ayu (Plecoglossus altivelis altivelis) fish population in Lake Biwa to the next generation was investigated by isotopic approaches. δ15N values of eggs in adult ovaries distinctively differed between the two types. Contribution of Koayu, calculated using δ15N values of spawned Ayu eggs, was much greater than that of Ooayu in general, as previously reported. Ooayu spawned more eggs in the upper area of the spawning ground and did so late in the season. These results show the potential of isotopic approaches for identifying maternal life-history types of spawned eggs of migratory animals.