Fish in the fast lane

Natural History, May, 2002 by Stephan Reebs

Love can sweep you off your feet (or fins), but for one species of freshwater fish, being swept away is the last thing an amorous male would want.

Rhinogobius is a small goby that lives in streams and rivers in Japan. During the reproductive season, the male builds a nest by clearing a space underneath a stone in a shallow area known as a riffle. Then he moves to deeper pools and tries, through energetic displays, to convince females to come spawn inside his nest. Two researchers at Osaka City University, Daisuke Takahashi and Masanori Kohda, have found that females are attracted to males that display in stronger currents within the pools. Not necessarily the biggest in absolute terms, these successful males are nevertheless rather heavy relative to their length.

According to Takahashi and Kohda, a female may use a male's performance in a fast current as an indication of his physical condition and his energy reserves. These are important, because after a female chooses a male and lays her eggs in his nest, she departs, leaving the male to guard the eggs, a task to which he devotes himself assiduously for two weeks. With no time for foraging, males sometimes cannibalize some of the eggs under their care. Healthy males with abundant energy reserves may be less likely to succumb to temptation, which may explain the females' preference. ("Females of a Stream Goby Choose Mates That Court in Fast Water Currents," Behaviour 138, 2001)

Stephan Reebs is a professor of biology at the Universite de Moncton in New Brunswick, Canada. He is the author of Fish Behavior in the Aquarium and in the Wild, recently published by Cornell University Press.