SCT counting tunnels can be used by both the SR-1101 and the SR-1601 fish counters. The SR-1101 counts with only one tunnel but is able to discriminate between upstream and downstream fish movements. Conversely, the SR-1601 counts up to sixteen tunnels but does not discriminate between upstream and downstream fish movements.
The standard SCT-1, 2, & 3 counting tunnels are 1, 2, and 3 inch diameter respectively. They all have a tapered entrance to prevent abrasive damage to fish. Counting tunnels are fabricated from PVC with stainless steel electrodes.