Oviposition decisions are mediated by spawning site quality in wild and domesticated zebrafish, Danio rerio

In oviparous species a female's choice of oviposition site can have a significant impact on off-spring survival and thereby on reproductive fitness. Here we compare the spawning behaviour of domesticated zebrafish, Danio rerio, in the laboratory with wild fish in a field-based mesocosm study in Bangladesh. We manipulated spawning site characteristics in order to examine oviposition decisions by females. In the laboratory experiment zebrafish were provided with a choice of four discrete spawning sites containing gravel or silt, with or without vegetation. We observed the behaviour of females and territorial males during spawning and recorded the number of eggs deposited in each spawning site. A gravel substrate was preferred by both males and females and vegetation was preferred over non-vegetated substrates. We repeated the experiment in Bangladesh and found the same substrate preference, although we failed to detect a significant effect of the presence of vegetation. When eggs were incubated under all four treatments, it was shown that egg survival was greatest in gravel, suggesting an adaptive explanation for zebrafish oviposition decisions.