Differences in Reproductive Behavior between Spawning and Non-Spawning Zebrafish Pairs and the Effects of 17α-Ethinylestradiol (EE2)

Reproductive success manifested by spawning and fertilization, in most fish, depends partly on an appropriate courtship behavior by both sexes. The zebrafish reproductive behavior can be resolved in some of its constituent elements by a computerized vision system and described in unbiased quantitative terms. Pairs of adult male and female zebrafish were monitored with automatic video tracking at 16 Hz for 45 min in a tank with a spawning area in one corner. Subsequently, spawning, if any, was registered and the swimming behavior and mutual interactions of the two fish were quantified. Further, temporal and frequency distributions of average velocity and turning rate were produced. It is demonstrated that the courtship behavior in spawning pairs differs markedly from non-spawning pairs with differences in both male and female behavior. EE2 (17α-ethinylestradiol), a contraceptive hormone found in aquatic environments, has only a slight effect on these behavior differences between spawning and non-spawning pairs.