On the way into the butterfly house there is a walkway that is pretty much in darkness. I assume the dark is to discourage the butterflies from escaping as they like the light and will avoid flying into the dark should the door be left open. I might be wrong but it does sorta make sense. Anyway along this short dark corridor are fresh water and salt water aquariums.
I turned on the on camera flash and focused on something that wasn't moving in the hope that a moving fish would just happen to land in the shot. This only worked because of the image stabilizer in the lens that I was using. It helped to keep the camera steady and the flash helped with the faster shutter speed. I shot maybe a dozen photos of the fish and of that dozen I am happy with about 8 of them. A pretty good hit rate!