High-speed camera recordings uncover previously unidentified elements of zebrafish mating behaviors integral to successful fertilization

The mating behavior of teleost fish consists of a sequence of stereotyped actions. By observing mating of zebrafish under high-speed video, we analyzed and characterized a behavioral cascade leading to successful fertilization. When paired, a male zebrafish engages the female by oscillating his body in high frequency ( quivering ). In response, the female pauses swimming and bends her body ( freezing ). Subsequently, the male contorts his trunk to enfold the female’s trunk. This behavior is known as wrap around . Here, we found that wrap around behavior consists of two previously unidentified components. After both sexes contort their trunks, the male adjusts until his trunk compresses the female’s dorsal fin ( hooking ). After hooking , the male trunk slides away from the female’s dorsal fin, simultaneously sliding his pectoral fin across the female’s gravid belly, stimulating egg release ( squeezing/spawning ). Orchestrated coordination of spawning presumably increases fertilization success. Surgical removal of the female dorsal fin inhibited hooking and the transition to squeezing . In a neuromuscular mutant where males lack quivering , female freezing and subsequent courtship behaviors were absent. We thus identified traits of zebrafish mating behavior and clarified their roles in successful mating.