Conditioned-response experiments show that both bony fishes and selachians have surface thermal receptors. Electrophysiological studies have demonstrated in selachians two mechanisms which could provide continuous information about constant temperature conditions—the ampullae of Lorenzini and the lateral-line system. In other fishes only one such mechanism has been demonstrated, namely the trunk lateral-line system. Impulses from the ampullae and the lateral-line organs are, apparently, always being poured into the central nervous system at a rate which is characteristic of the temperature of the environment. The change in frequency of these action potentials with a given change in temperature is not great and there is no sign of adaptation. These sensory receptor mechanisms could operate in such a way as to give fish an absolute sense of temperature. In addition to this non-adaptive effect of temperature on these two kinds of receptors, there occurs, in the ampullae of Lorenzini only, another spectacular change in frequency of the nerve impulses with change in temperature, and this response is adaptive. This effect disappears with continued exposure to the new temperature, and the spontaneous impulses gradually assume the stable frequency which is characteristic of the temperature.The principal effects of temperature on the activities of fish are as follows: Fish moving in a temperature gradient select a particular temperature because of an effect of the gradient temperatures on their movements. When fish move through the temperatures of a gradient, the frequency of their movements is least in the selected region. Moderately rapid changes of temperature do not elicit locomotor responses from resting fish until very high temperatures are reached, but do affect the frequency of movements of active fish. The frequency of spontaneous movements is related to the equilibration temperature, being greatest at the temperature ordinarily selected by the same fish if placed in a temperature gradient. Maximum cruising speed, as measured at different equilibration temperatures, is greatest at the selected temperature, as is also the distance moved in response to an electric shock. The maximum cruising speed that can be maintained by fish increases, with acclimation temperature, to a peak at the final preferendum.Temperature selection by fish in a gradient is a function of surface thermal receptors not in the trunk lateral line, and of the forebrain. The relation between frequency of spontaneous movements and equilibration temperature depends in some way upon the integrity of the cerebellum.There are a few instances where a correlation has been demonstrated between temperature conditions and behaviour of fish in nature because of the effect of temperature on activity. There are other instances in which distribution of fish in nature appears to be correlated with temperature as a result of selection responses to temperature gradients.
The effect of temperature, gradient, and load carriage on oxygen consumption, posture, and gait characteristics