Posted: Sat Mar 13, 2010 8:08 pm
Both my RES do this. It could be because they see their reflection (like coreyvht said) or because the glass is clear and they see that there is something beyond it and try to reach it. RES don't usually exhibit this behaviour if they are in a container that doesn't have see-through walls.
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Tank #1:
~Charlie - 4 inch male RES
Tank #2:
~Charlotte - 6 inch female RES