Strange behavior coming from my pygmy angelfish

[friendofgum]

I've had this pygmy angelfish for about five months or so, and it's been great. Getting along well with tankmates, eating normally, etc. The past couple days or so, however, I've noticed it doing a strange, neurotic-type behavior: there's a spot on the side of the tank where the heater is suctioned on, and it swims rapidly up and down, up and down, with its face against the glass, over and over again on either side of the heater. It almost looks like it's trying to get through the glass. I'm wondering if maybe it sees its reflection and is displaying aggression towards itself, or...? But it's never done this before a few days ago, and it's beginning to trouble me. Also noted, I have no idea what the fish's sex is, so I wouldn't know if it's male aggressive behavior or neurosis or what.

I'm thinking about putting some kind of sheet or paper in that area to block the fish from seeing anything on that side. Do you think this would fix the problem?

 

[pktech]

It can't hurt to try - I had a coral beauty tht did that exact thing & I was concerened. I could only guess whether the reflection or somebody was stressing it out. It would eventually stop, but the up & down was alarming. Does it eat ok now? Is it aggressive towards it's pals? Did you add anyone new or did you do a recent water change?