A friend of mine rescued a fish from her irresponsible neighbours. They attempted to clean their small fishtank and the water they used for that was boiled. Recently. Then they went to get her opinion because the fish "was behaving strangely". She said that the moment she put her hand in the fishtank, she reflexively took it out, so hot it was. Immediately she caught the fish with her hands and put it in a cup of home-temperature water.
The fish lived through the night in a small container and in the morning she got a fishtank with all equipment, and even bought some plants for it. The fish behaves normally, eats normally. It is a male betta, no idea how old it can be.
There appears to be a thin layer of something on his scales. The scales are whole, not sticking out, no scales loss. What do you think it can be? Could you give some advice what else can she do for the fish?