Can fish die because of aggression?

Question
One of my mollies died today :(
It had its gills swollen and body thinned out. But I dont think it was any disease. What I think it was that due to aggression from other molly and platy, it wasnt eating much and became thin.
But anyways its dead today. What could it be? Can fish die due to aggression?
Is my other fish in danger of some disease, parasite? What can I do to prevent it?

Answer
Hi there,
Sorry to hear that.

It's always possible fish could die of too much stress. But it could have also been internal parasites. A thinning body and loss of a appetite can be a sign of internal parasites. Stringy white or clear waste is also a warning sign. Internal parasites can wreck havoc on fish and it can be difficult to treat, involving feeding a special anti-parasite food and treating the water with salt/medications.

I hope none of your other fish develop this. The best way to prevent this is keep up with water changes and be careful of any live food you give to your fish as they can be transmitters of parasites.

Best of luck, I hope this helps!
Karen~