Flow sensing in the deep sea: The lateral line system of stomiiform fishes

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Fishes inhabiting the deep sea are notable for the production of bioluminescence and specializations of their visual systems. However, they are also equipped with non-visual sensory systems that probably mediate critical behaviours as they do in other fishes, but they are not well-studied. The mechanosensory lateral line system of fishes in the order Stomiiformes, the largest and most diverse order of deep-sea fishes, was studied in detail in 28 species (in 17 of 52 genera, in all four stomiiform families) using several morphological methods. Some or all of the narrow cranial lateral line canals are partially reduced or absent in representatives of all genera examined. In addition, hundreds to thousands of small superficial neuromasts were found on the head and body in 17 species in 11 genera of sternoptychids, gonostomatids and stomiids. Reported here for the first time, this feature of the lateral line system would enhance sensitivity to the velocity component of water flows (probably of biotic origin) and is hypothesized to be an adaptation in the low-light environment of the deep sea. These observations require that we think beyond vision when considering the behaviour and sensory ecology of these critically important and globally distributed deep-sea fishes.

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Zoological Journal of the Linnean Society