What do you mean by aggressive?

Sometimes my loaches will chase each other in play - but don't harm one another.

He was pestering and poking at him and when he would swim away just kept coming at him. Today he seems to have settled down. These guys are fun to watch!

I think they were probably just getting to know each other. Clown loaches definitely love to hang out with their own kind.

Clown loaches have a sharp razor like "plate" on either side of their little cheeks, that they flip up during a fight, mine were pretty aggresive towards each other and other fish, the older they got the worse they were, I had three that got to be about the size of a computer mouse, crazy little critters they are!