Observations have been made from submersibles on the behaviour of certain mesopelagic fish. These have revealed that some species of Myctophid at night swim horizontally but during the daytime rest in a head-upwards or head- downwards position. This orientation must obviously reduce the size of their shadow when viewed from below. These fish have forwardly directed eyes, so the head-up attitude must assist detection of shadows above them. A variety of animals including fish such as eel pouts, have been observed to curl up and hang motionless when startled or attacked (Robison, 1995). Some scientists believe this may be a form of mimicry designed to hide them from predators. In the gloom, rounded shapes are usually associated with unpalatable animals such as medusae.
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