THE ROLE OF THE SENSORY SYSTEMS OF HERRING LARVAE IN EVADING PREDATORY FISHES

Herring (Clupea harengus L.) larvae, ranging from 8–35 mm T.L. were subjected to predation by juvenile herring and sprats (Sprattus sprattus L.) ranging from 80–160 mm T.L. Responses to attacks and non-threatening encounters were recorded by a TV system operated with infra-red light, which was invisible to both predator and prey. Records were made in both light and dark with larvae before and after the otic bullae filled with gas, before and after lateral line canal formation, and before and after chemical ablation of the neuromasts with streptomycin. Larvae often responded with a C-start, turning away from the stimulus source, both in dark and light. Attacks on larvae occurred only in the light. Responsiveness to attacks was very low in the smaller larvae but increased as the otic bulla filled with gas and the lateral line canal developed. Larger larvae responded more often to attacks than to non-threatening encounters with predators. Vision seems to inhibit unnecessary responses since responsiveness was lower in the light than the dark for non-threatening encounters. Response distances were generally short, only 2–4 cm, with no substantial differences associated with sensory capability. In dealing with a predation risk, young larvae appear to depend on being inconspicu ous (transparent, inactive), whereas older, more opaque larvae actively evade capture. © 1990, Marine Biological Association of the United Kingdom. All rights reserved.