Researchers were able to train the fish to hit targets at various heights, then filmed them in action to observe the mechanisms behind the shot. They found that the fish were adjusting their jet stream to hit each target with maximum impact, whatever the distance. The fish adjusted the jet by changing the way they moved their mouths: Starting with an open mouth, a spitting fish closes its mouth partially to create a smaller, more focused stream of water. By closing its mouth more slowly, the fish creates less acceleration. This slower stream is designed to hit a distant target with more impact. By closing its mouth quickly, a fish creates a highly accelerated stream that's ready to hit a close target at optimum force.
This physiological trick, the researchers said in a statement, could potentially be used to create better human-built nozzles.