It never occurred to me to ask the question, until last night. We have a fish in an aquarium in the corner of our dining room. I think he is a char — we caught him in a pond as a minnow so I have never been sure.
He doesn't get upset easily; I can move around the room without disturbing him and we went all the way through Thanksgiving — setting up the table, eating and cleaning up — without his showing any sign of stress.
He can clearly see what is going on. When I come down in the morning, he swims to the corner (closest to the kitchen) and wags his tail, waiting for me to feed him as is the daily ritual.
But last night, after clearing the table, I figured we would switch directly from Thanksgiving to Christmas, but as I moved towards the table to put on the new tablecloth, our fish (Sam) suddenly started splashing and darting back and forth in alarm. Something had set him off.
What was it? I occasionally take him by surprise and he splashes and hides behind his rock. But this time he was more alarmed than usual. And I wasn't even that close to his aquarium. But there was one difference: I was carrying a bright red tablecloth.
The bright color red had triggered something in him. He was very agitated until I had the tablecloth on the table. Once it stopped moving, he calmed down. I hadn't seen behavior like this since he was a very young fish (and not accustomed to his environment).
So, do fish react to the color red like the proverbial bull? Or would it be anything bright and moving that triggers a defensive response? He hasn't reacted to colored shirts or other materials that I noticed. Whatever the cause, the result was dramatic.