Guppy agression or fin rot?

[KimmiA]

I recently adopted a guppy about 3 weeks ago and added her to my 15g with 2 other females and 2 males. When I went over to the tank this morning I noticed that the newest female guppy's dorsal fin was nearly gone.

This female is much smaller than the other two females, and I'm questioning if this is a case of aggression, or could this be fin rot?

I transferred her to a 20g juvie tank I have set up for the time being. When I tried to net her, she was very skittish and was already hiding in some plants, which makes me think she experienced aggression in the tank.

Thoughts? Thank you!

 

[dmolavi]

I have the same problem, and based on the all knowing and all powerful Google...it would appear that it's due to a skewed male/female ratio in the tank.

Everything that I've read says to have approx 3 females per male; that way the males aren't nipping each other, and you don't have them all accosting the same female, or each other.