Why do archerfish spit water?

Answer: Shooting down insects to eat

Defending territory boundaries — The familiar aimed water jets knock food into reach rather than mark territorial boundaries. Their target is an insect above the water, not a line around the fish's home area.

Cleaning their gill filters — These outward-directed jets are a hunting tool, not a way to wash the gills. Water used in breathing passes over the gills inside the head; the aimed jet instead strikes prey above the surface.

Shooting down insects to eat ✓ — Archerfish shoot jets of water to knock insects from positions above the surface. They adjust their aim despite the bending of light at the air-water boundary. Once the prey falls into the water, the fish can capture it.