Determinants of male mating success in a natural population of a stream goby of the genus Rhinogobius

The mating success of individually identified males of a stream goby, Rhinogobius sp. CB (cross‐band type), was recorded over one breeding season. One to 3 year‐old males were active in mating, but 3 year‐old males, which accounted for 36% of the population, amounted to c . 70% of the total males guarding eggs in the nest. Three quarters of the breeding males had only one brooding cycle, but the others had two or three. All the latter males changed their nest sites between cycles within a riffle. In 1 and 2 year‐old males, the number of brooding cycles contributed more to the mating success than egg mass size in one brooding cycle. For mating success of 3 year‐old males, the egg mass size in one brooding cycle, which can be enhanced by spawning with a large female or multiple females, was as important as the number of brooding cycles. These male reproductive tactics could be attributed to the age‐related ability of nest construction and mate acquisition.