Q: PZ Wrote,
We recently moved our betta to a cycled, planted, 10-gallon tank with a filter and a heater. He is acting VERY oddly, now that he is in the tank. He hangs out right next to the filter, flaring and puffing out his cheeks, and bumping the glass with his nose. I thought the flow of the filter might be bothering him, so I shut it off. He is still doing it though. When I remove the filter he stops.
Could he be mistaking the filter for another Betta?
A: The behavior you are describing sounds very much like a male Betta’s typical response to another male Betta or in this case, his reflection. Your tank’s filter is probably casting a shadow or blocking glare so that he is able to see himself in the reflection of the glass near the filter. This type of behavior is harmless and the frequency in which he is flaring should become less in a few days. If it remains a problem, you can place some plants (real or silk) around the filter to break up the sight lines. Go ahead and turn the filter back on and give him a little time to get used to the new tank and its reflections.