my poor lonely puffer

"Nick Chan" wrote in news:1158892542.543057.202560
@k70g2000cwa.googlegroups.com:

i think it's a brown puffer, not sure, about 5.5inch

Looks active the first day though. Do they have the ability to change
colour?

I mix him with 2 scats and a kind of cleaner fish

Many fish can change colour--it is usually a sign of mood. Stressed fish
often appear faded or very dark depending on the species.

Judging from his stereotypic behaviour in the video he does appear to be
stressed, but he is active so he is probably healthy otherwise.

My guess is environment. If your water specs are on par for that fish then
perhaps it is due to lack of cover or due to interference from the other
fish in the tank. Scats are very active fish that can occasionally be
belligerent; they may be playing a part in stressing your puffer too.