Predation strategies of larval clownfish capturing evasive copepod prey

Abstract

Fish larvae depend on finding and capturing enough prey for rapid growth during the planktonic phase. The diet of many fish larvae is dominated by copepods, small crustaceans that are highly sensitive to hydrodynamic disturbances and possess strong escape responses. We examined how fish larvae with immature jaws, musculature and fins capture such evasive prey. The kinematics of feeding attempts by larval clownfish Amphiprion ocellaris on 3 developmental stages of copepod Bestiolina similis were investigated using high-speed videography. A stealthy approach brought the fish larva within ~1 mm of the copepod; shortest distances were observed in early larvae (1 to 5 d post-hatch [dph]) attacking immature copepods. Peak speeds during strikes increased with fish age and copepod developmental stage (150 to 250 mm s -1 ), with time to capture <8 ms on average. Most successful captures (70%) were of copepods that failed to initiate an escape response during the strike. If a copepod initiated an escape, capture success decreased to ~50% for nauplii and copepodites and 25% for adults. Adult copepods were more likely to attempt an escape response than copepodites or nauplii. Prey stage and the interaction between strike distance and speed were the parameters that best fit a logistic regression model to the observed captures and escapes. The successful switch to larger and more evasive copepod prey by A. ocellaris larvae did not occur until 7 dph and coincided with ontogenetic changes (post-flexion) and a predatory strategy that included shorter approach phases and greater strike speeds.