The simplest shrimp traps consist of a bamboo fencing or screen leader, running from the pond bank into the catch chambers. Shrimp moving along the bank will be led to the chambers, where they can be collected. Sometimes a grating is placed at the entrance to guard against the entry of large crabs, which might prey on the shrimp. The pound-net, originally developed in Japan, is an improvement over bamboo traps. Pound-nets use netting rather than bamboo, and can therefore select preferred shrimp sizes more effectively by changing the mesh size of the catch chambers (Fast, 1992).