Effects of organism and substrate size on burial mechanics of English sole, Parophrys vetulus

Flatfishes use cyclic body undulations to force water into the sediment and fluidize substrate particles, displacing them into the water column. When water velocity decreases, suspended particles settle back onto the fish, hiding it from view. Burial may become more challenging as flatfishes grow because the area to be covered increases exponentially with the second power of length. In addition, particle size is not uniform in naturally occurring substrates, and larger particles require higher water velocities for fluidization. We quantified the effects of organism and particle-size scaling on burial behavior of English sole, Parophrys vetulus. We recorded burial events from a size range of individuals (5–32 cm total length, TL), while maintaining constant substrate grain size. Larger fish used lower cycle frequencies and took longer to bury, but overall burial performance was maintained (∼100% coverage). To test the effect of particle size on burial performance, individuals of similar lengths (5.7–8.1 cm TL) were presented with different substrate sizes (0.125–0.710 mm). Particle size did not affect cycle frequency or time to burial, but fish did not achieve 100% coverage with the largest particles because they could not fluidize this substrate. Taken together, these results suggest that both body size and substrate grain size can potentially limit the ability of flatfishes to bury: a very large fish (>150 cm) may move too slowly to fluidize all but the smallest substrate particles and some particles are simply too large for smaller individuals to fluidize.