Reproductive behaviour of wild zebrafish (Danio rerio) in large tanks

Zebrafish are an intensively studied model organism, and yet there are no studies describing the reproductive behaviour of wild zebrafish. Here we investigated the reproductive behaviour of wild-caught zebrafish (Danio rerio) from India in large (1100 l) aquaria containing gravel and plants and low population densities. We observed the behaviour of focal individuals in groups of eight fish (equal sex ratio; 28 replicates; 42 h total observations), and found similarities to what has been previously described for domesticated fish in small aquaria. However, we also found several notable differences and, in particular, we found that the fish usually spawned in pairs rather than in groups, and we found evidence for sexual selection. We conducted additional observations of wild-derived fish in smaller, conventional aquaria (17 l) and high densities, and found that group spawning is more common in these conditions. Taken together, our observations suggest that high rates of group spawning may be an artefact of small aquaria, which may reduce or eliminate sexual selection by giving more opportunities for sneaky males and preventing females' from choosing their mates.