Size-dependent male-male competition for a spawning substrate between Pseudorasbora parva and Pseudorasbora pumila

Pseudorasbora parva, a species native to western Japan, has been accidentally introduced into eastern Japan, where P. pumila is indigenous. We investigated inter- and intraspecific, male-male competition between P. parva and P. pumila for acquisition of spawning substrates in an experimental setting. Within each species, males of larger standard length and heavier body weight were more successful in acquiring a substrate. Males of the two species competed, but the outcome was determined primarily by body weight. This interspecific, size-dependent, male-male competition might be an important factor in the species replacement of P. pumila by P. parva.