Leptocephalus curling behavior
These video recordings show leptocephali curling behavior in surface waters at night at Osprey Reef in the Coral Sea, Australia.
Six of the 21 larvae filmed on 10 different nights between August and October of 1999, 2000, and 2001 displayed a distinct shape-change behavior of curling up into fully or partially coiled shapes.These three video clips show this unusual curling behavior and are associated with a soon to be published scientific paper.
The transparency and gelatinous consistency of the leptocephali performing these behaviors results in the coiled leptocephali resembling the typical body shapes and consistency of gelatinous zooplankton such as jellyfish, ctenophores, siphonophores and salps. Due to either stinging defenses or low food value, many fishes avoid consuming gelatinous zooplankton, so the curling behavior in response to threatening situations may result in mimicry of these organisms. This could provide leptocephali with higher survival rates compared with attempting to escape from pelagic predators that are close enough to detect them.
Video 1 - Video recordings at Osprey Reef of the curling behavior of a Conger leptocephalus (L15) that formed a tightly coiled round shape before swimming away, but then started to curl up again briefly; and the curling behavior of a chlopsid leptocephalus (L4) that showed a completely coiled shape and then also formed a partial coil part of the time with its tail region extending out from the coil.
Video 2 - Video recordings at Osprey Reef of the curling behavior of two muraenid leptocephali (L7 and L18) that formed much flatter oval-shaped coils and also sometimes made less tightly-coiled shapes. The L18 larva attempted to hold the tightly-coiled shape even while being moved past the diver by water currents.
Video 3 - Video recordings at Osprey Reef of the curling behavior of a larger-sized more elongated congrid leptocephalus of the genus Ariosoma (L17) that never formed a fully coiled shape with its whole body, but formed a very tight coil using the anterior part of its body and maintained the posterior part of its body extending out from the coil; and the curling behavior of a large muraenid leptocephalus (L3) that had an unusually deep body and curled up to a lesser degree by forming a partial coil with the anterior part of its body or a large open circle using its whole body.
Mark McGrouther , Collection Manager, Ichthyology