Exploring the effects of size and age on vulnerability to predation of larval zebrafish (Danio rerio)

Abstract

Predation is a leading cause of mortality in the yolk sac larval stage of teleost fish. Size and age are known to impact larval vulnerability to predation, but how they do so have been debated. The bigger-is-better hypothesis that proposed large larvae have fitness advantages over their smaller counterparts has come under scrutiny as most studies that support this hypothesis only consider proxies for probability of capture. A less explored hypothesis suggests that the benefits of size vary with each day, where it could be beneficial to be small or large depending on external conditions. This study seeks to expand on this hypothesis by exploring the effects of size and age on proxies of probability of encounter and probability of capture during the yolk sac stage of zebrafish larvae (Danio rerio). Direct yolk sac manipulation attempted to create larvae of distinct size groups at hatch, but it was found unsuccessful as the control and reduction groups were not significantly different at hatch (p = 0.878). Instead, larvae were split into large and small groups from the top and bottom 25% from standard length that varied in size from 8 to 22. Probability of encounter was estimated from free swimming trials which measured distance travelled (mm) and mean velocity (mm/s). Probability of encounter was estimated from escape response experiments, where larvae experienced a tactile stimulation. It was found that large larvae moved significantly further distances on day 4 (p = 0.00835), and significantly faster on day 3 (p = 0.00813). Escape response was measured as distance travelled (mm), mean velocity (mm/s), max acceleration (mm2/s), and latency to respond. It was found that small larvae travelled significantly further on day 2 (p = 0.00216), but large larvae responded quicker to a threat than small larvae on day 2 (p = 0.00399). The estimates of probability of encounter and probability of capture in this study do not indicate that age or size effect the vulnerability to predation of yolk sac zebrafish larvae. This suggests small larvae are not at a fitness disadvantage to large cohort members, potentially providing the beginning steps to a counter argument of the bigger-is-better hypothesis.