At the arboretum where I photograph the real koi, you’re not allowed to touch them. They have a slime coat that is vulnerable to injury if millions of hands reach out to pet them, day after day, season after season. Nobody told the koi, these koi who are always hungry no matter how much food they’ve eaten, and they are remarkably outgoing and indiscriminate in their affections. I must look exactly like all the other humans to them, especially the ones with the bags of food, so they come up to the surface and are very available for petting.
Not that I pet them. I never pet them. There’s a sign right there telling you not to pet them. I obey the sign, but it’s perfectly obvious that the koi cannot read.
However, I can pet my own fish anytime I want. Mine have a wax coat. It’s vulnerable to smudging, but I’m careful not to smudge my fish.