Acquired versus innate prey capturing skills in super-precocial live-bearing fish.

Live-bearing fish start hunting for mobile prey within hours after birth, an example of extreme precociality. Because prenatal, in utero, development of this behaviour is constrained by the lack of free-swimming sensory-motor interactions, immediate success after birth depends on innate, evolutionarily acquired patterns. Optimal performance however requires flexible adjustment to an unpredictable environment. To distinguish innate from postnatally developing patterns we analysed over 2000 prey capture events for 28 metallic livebearers (Girardinus metallicus; Poeciliidae), during their first 3 days after birth. We show that the use of synchronous pectoral fin beats for final acceleration and ingestion is fixed and presumably innate. It allows for direct, symmetrical control of swimming speed and direction, while avoiding head yaw. Eye movements and body curvatures, however, change considerably in the first few days, showing that eye-tail coordination requires postnatal development. The results show how successful prey captures for newborn, live-bearing fish are based on a combination of fixed motor programmes and rapid, postnatal development.