Think of that glow stick you get at ball games. You have to bend it to make it light up. Bending the stick breaks a glass vial inside, which allows two chemicals to mix. The males spit out tiny balls of bioluminescent material that leave glowing trails of dots and dashes. The pattern and orientation of the trail identifies the species of seed shrimp.
Females watch for the watery sparks and swim over to find the perfect match.
The Angler fish has a spine-like appendage that slants forward like a fishing pole over its mouth. At the end is a fleshy organ that's lit up by bioluminescence. We're Block and Byrd for Earth and Sky.