The effect of a depth gradient on the mating behavior, oviposition site preference, and embryo production in the zebrafish, Danio rerio.

Captive zebrafish (Danio rerio) exhibit a limited repertoire of mating behaviors, likely due to the somewhat unnatural environment of aquaria. Observations in their natural habitat led us to believe that a depth gradient within the mating setup would positively affect fish mating. By tilting the tank to produce a depth gradient, we observed novel behaviors along with a preference for oviposition in the shallow area. Although we did not see an increase in the likelihood of a pair of fish to mate, we did see an increase in the embryo output in both adults and juveniles. In the adults, tilting led to a significant increase in embryo production (436 +/- 35 tilted vs. 362 +/- 34 untilted; p < 0.05). A similar effect was seen in juvenile fish as they progressed through sexual maturity. These results suggest that tilting of mating cages in the laboratory setting will lead to demonstrable improvements in embryo production for zebrafish researchers, and highlights the possibility of other manipulations to increase fecundity.