Pacus (tested with the Gulp Fish living in my colony) will attemp to swim through open mechanized airlocks, but once they do so, they can not leave. They become glum and confined as they would in a wall. Dividing a tank in two and showing their pathing confirms that they do think they can swim through, the “show pathing” lines are indicated as per normal inside the airlock and on the other side of the tank. Upon attempting to swim through the airlock, these pathing indicators disappear and the fish becomes trapped.
These airlocks are opened by automation wire hooked up to a clock sensor.
Divide a tank of pacus in two with mechanized airlocks, then use automation to open them.