Many of the reef fish in our California seas are territorial or just plain curious. When confronted with their own image in a mirror, they become pugnacious or confrontational, even confused. Prop up a mirror on the reef and watching the ensuing behavior patterns will be at the least, entertaining, but also educational.
Do not take a glass mirror underwater. The risk of breakage is too great. Plastic or metal mirrors are readily available at sporting goods stores in the camping or backpacking section. They are usually small enough to fit in a BC pocket without the fear of shattering.
The California State Marine Fish is your best candidate for underwater mirror fun. They are fiercely territorial and will confront any intruders, especially other adult garibaldi of the same sex. They will approach their own images in a head down, confrontational posture. Listen for the popping they often make in the throats to ward off intruders. Biting will ensue. As they realize the match is a stalemate, the fish will spend more time studying its image than confronting it, trying to figure out how to get the upper hand. This action can last an entire dive.
Sheephead are also territorial, although considerably less so than garibaldi. They are, however, much more curious and, to some degree, gregarious. Sheephead will sometimes bite at their own image, mouth wide, but more often than not they will just study this strange fellow fish. I have also seen sheephead actually look behind a mirror, an unusual behavior normally only seen in animals of higher intelligence.
The sarcastic fringehead is the most ferocious fish in California waters. Fortunately they are not very large—about six to eight inches. When confronted, by anybody or anything, including divers, they will exhibit a dramatic behavior. Their dorsal fin has a metallic blue dot. They will raise this high and open their mouth large. Their gill plates on the male shine bright yellow and mouth opening can be as large as half their body length. Watch out! This is often followed by a viscous attack and a sharp, powerful bite.
A mirror will precipitate an immediate response, display, and attack (fortunately on the mirror, not you). The spectacle usually does not last long but is well worth it. Sarcastic fringeheads can be found on sand and mud flats and in submarine canyons.
OTHER FISH AND MARINE LIFE
When it comes to nesting and mating, painting greenlings can be ferocious. They go into dramatic color changes and spasmodic dances. Usually they do not react to a mirror but when they do, watch out—the ensuing spectacle can be quite fun.
Sometimes lingcod will react to its own image. But watch out. If they attack they have sharp teeth, so keep your hands clear.
Other fish that sometimes react to mirrors include gobies, rockfish, and perch. And other critters will sometimes respond. Crabs sometimes behave strangely when confronted with their own image.
For even more fun, try more than one mirror. Make kind of an underwater “fun house” room of mirrors. Fish will not know what intruder to turn toward. Also, turn a mirror slightly up so that it reflects the surface. Fish seem to perceive this as a “hole” in the reef and try to swim through it only to be confronted by another oddly similar looking fish swimming back the same way.
Experiment. Nearly all animals will react to one degree or another but in uniquely different ways.