Rainbow Fish And Behavior

[tameem]

My cute rainbow shark that I have has always been busy foraging the tank for alge, on the plants and decorations. Sometimes if other fish gets in his way, he will chase them, but only briefly and continue doing his own thing. Today I notice him swimming and staying in place sometimes, and not nearly as active. He looks fine and nothing physically a problem, I just noticed that his behavior was different then before

Any reason I should be concerned? Its not often I see him in one place swimming, he has always been real active.
Here is a pic of him.

 

[tameem]

anyone want to respond to my question? this evening I notice him just hanging around, swimming in one spot, and more or less stationary. He looks healthy. I also never really saw him eat any flake food or anything I dropped in the tank, he was always so consumed by the grazing of algae.

Any ideas? or am I worried for no reason?
I try to be meticulous with my tank water and do 20% water changes weeking, and I test water all the time, 0 nitrites, 0 ammonia.

Thanks

Okay,
I need to add to this and say the cute fish also is sometimes resting on the decorations, or closer to the substrate. IM getting real concerned now anytime a fish is near touching the decoration or foor withuot moving around...??

 

[tameem]

well, everyone thanks so much for your overwhleming responses to my posting! Tonight I came home and learned that my rainbow fish died, and his eyes eaten out. I removed the body. Maybe I could have taken some action if I had some information or helpful replies to my posting, but its too late!
I must say Im pretty disapointed. Perhaps I should have posted in the emergency forum, instead.