Fins Nipped By Who?

[wantmorefish]

Ive had my fresh water tank for about 2 months. I have two pink skirted tetras, one male fan tailed guppy, one female guppy, and a cory catfish. I recently introduced another female semi-pregnant female guppy, and 4 small ghost shrimp. About two day later I have noticed that my male guppy's back fin is nipped in two places. Who nipped it? Ive been watching all of my fish and I cant figure out who did the nipping. Maybe someone can give me some feedback.

 

[VaegaVic]

All of those fish can nip, except the cory.

Tetras need to be in shoals, if not, they can feel very insecure and turn aggressive, 5 or more ideally.
Male guppies also nip, as do females on occasion.

 

[wantmorefish]

I only have one male and he is the one getting nipped. Everyone was fine together, the tetras and the one female, but then when I put the other already pregnant female guppy in the tank two days later the nipping of the male started. I only have a 15 gallon for now so I dont want to get more tetras. Got any other advice? Thanks for the other.

 

[VaegaVic]

AH sorry I misread, so you only have 1 male.
I would still seriously put my money on the tetra, especially that species of tetra, at feeding times they can get rather excited. They normally take out the excitement on each other, but in such a small group...

You have more than enough space for a whole shoal of tetras in a tank that size! Really, the store you bought them from should have told you this.

 

[wantmorefish]

So you think I should get some more skirted tetras? How many do you think I should get?