The role of fanning behavior in water exchange by a nest‐guarding benthic fish before spawning

Abstract

Lay AbstractIn some species of fish, males provide parental care and fan within nests before eggs are deposited. Courtship fanning behavior by the male may serve to advertise to females both his ability to disperse reproductive chemical signals and to ventilate eggs once deposited in the nest. We used a technique, called particle image velocimetry, to visualize and characterize flow both in and out of a nest generated by courting Round Goby males, a bottom‐dwelling fish. Once flow was characterized, we conducted a laboratory experiment to determine if caudal and pectoral fanning behavior was influenced by the presence of a female near the nest. The presence of a single female in the vicinity of the nest had no effect on fanning rates. However, there were significant differences between fanning behavior between types of fins. Fanning by caudal fins (with the tail at the nest entrance) resulted in water being pushed out of the nest. We estimated that caudal fanning currents propagated over a distance of at least 34 cm from the nest entrance (2–3 times the body length of an adult Round Goby). In contrast, fanning by pectoral fins (with the head at the nest entrance) resulted in flow entering the nest. Flow entering the nest was much lower than flow being pushed out of the nest. We speculate that by pumping water out of the nest with their tail, males disperse odors to guide reproductive females to the nest; whereas pectoral fanning serves mainly to ventilate the nest, denoting specialization of these locomotive structures as pumping and water stirring appendages.