red velvet swordtail

Question
Hi there -
I have a quick question about baby swordtails.  I purchased a red velvet swordtail a few weeks back to accompany a different platy and the day after I bought her, she had 7 fry that I caught and placed in the breeder tank.  She died unfortunately during the process.

The babies that I caught have done rather well.  My question is perhaps a silly one, BUT there are four VERY RED velvet looking swordtails and three that were white and over the last few days (they are 5 weeks old) have a PATCH of red now showing but are still mostly white with a line running down their backside that is getting darker each day.  They are much more aggressive than the all red ones.

Is this the difference between males and females?  Are the whiter ones the males and red one the females?  I know full grown males are the ones that develop tails, but the color difference at this point is so significant that I am thinking the swordtail I bought was breed with a different breed than the red velvet?

Should I separate the three that are getting aggressive? Could they be trying to mate already????

Thanks!
Maryann

Answer
Hi Maryann:

Congratulation on your new brood.  It sounds like to me that you have a variety of Swordtails.  Males will develop their swords when they are approximately three quarters grown.  Females will have a rounder shape and a gravid patch near their anus or the back of their stomach area.  I would guess that your female mother died due to stress as being pregnant and traveling to a new aquarium would likely be enough stress to shock her.  You more then likely are seeing a difference in genetics as opposed to different types of Swordtails.  As for separating them... if the white fry are causing damage of if you feel as though the continued interaction with the red fry would be detrimental to either group then I would separate them; otherwise I would let them stay in the same tank.  Fish develop a pecking order and that may be what you are seeing with the aggression.  Make sure  you have small food for the fry. My guppies love microworms and when my fry get to be about a month and a half old I start adding flake food... I just put it in a ziplock and crush it up small for them. Flake food is a good food right when you turn out the lights at night.  I hope this information helped... If you have any other questions please let me know... Dave