Salmon and Eel Movement in Constant Circular Current

Underyearling salmon in a circular pond of moving water at 20–25 °C. swam during the day and rested on the bottom at night. Before feeding they translocated actively upstream in rapid shallow water and in all directions in slow deep water. During feeding they held position in slow water, but made short excursions to seize food. After feeding, most moved into rapid, shallow water, the largest into the most rapid water.Translocating salmon usually went upstream and swam faster in more rapid water so that the rate of translocation remained constant. The rate of translocation increased with the size of the fish, more than doubling from 3 to 4 cm. in length.While steady illumination caused the salmon to swim up in the water from the bottom, a sudden change in light intensity when they were swimming, as by an object moving against the sky, caused them to swim quickly from shallow to deep water.Eels translocated upstream regularly only in the more rapid water, the swimming rate increasing with current rate. Eels 7 cm. long translocated almost twice as rapidly as salmon 3.5 cm. long. Eels burrowed in the gravel in bright daylight, came out in the evening and translocated rapidly even at night when the salmon were resting.