A device which is applicable to a temperature-selecting experiment for small-sized aquatic animals relates to a device which is used in the temperature-selecting experiment, which can guarantee that mixed channels form stable gradients, and the device only needs a water resource with two temperatures simultaneously, and experiment objects can freely swim in a running channel. The device has the advantages of stable temperature gradients, small size and simple and convenient operation, and comprises a circular device and a running water
system, wherein, the circular device is provided with four concentric circular walls on a flat board, the mixed channels are arranged between the number 1 and the number 2 circular walls, the running channel is arranged between the number 2 and the number 3 circular walls, a
water discharge channel is arranged between the number 3 and the number 4 circular walls, baffles are respectively arranged in the mixed channels, the running channel and the
water discharge channel, the circle center of the flat board is provided with a
water discharge hole, the top portion of the outer wall of the mixed channels is provided with an interface, 8 gaps are respectively arrayed on the number 2, the number 3 and the number 4 circular walls, the inner walls of two sides of the running channel are provided with screen meshes, the running water
system is provided with a high-temperature water-accumulating
barrel and a low-temperature water-accumulating
barrel and a water tube, the water tube is led out of the high-temperature water-accumulating
barrel and the low-temperature water-accumulating barrel respectively from the insides of the barrels, and is connected with the number 1 circular wall.