Wisenden zebrafish embryo early hatching

Plasticity in hatching time allows embryos to maximize fitness by
balancing benefits and costs of remaining bound within the chorion against
the benefits and costs of emerging as a free-swimming larva. In our first
experiment, we exposed zebrafish (Danio rerio) embryos to either chemical
cues from crushed embryos (simulating egg predation) or to blank water
control. Embryos exposed to alarm cues hatched sooner with shorter body
lengths and underdeveloped fins relative to larvae from the water
treatment. Burst swimming speed was significantly slower for larvae that
hatched from the alarm cue treatment. In a second 2 x 2 experiment, we
exposed zebrafish embryos to either chemical alarm cues from conspecific
embryos, mechanical disturbance (magnetic stir bar) to simulate a predator
probing the substrate for developing embryos, both chemical and mechanical
indicators of risk, or neither (control). We found similar effects in
terms of earlier time to hatch at an earlier stage of development and
poorer swimming performance of hatchling larvae. In the second experiment
these effects occurred in response to mechanical disturbance with or
without the presence of chemical alarm cues. Alarm cues alone produced no
effects in the second experiment. Taken together, these data indicate that
zebrafish embryos demonstrate a facultative tradeoff between risk of
predation acting on two stages of their life history.