Female Swordtails

Question
Oh my god, I am so full of questions about my fish.  I was recently given a 55 gal. tank.  2 wks later I was given 11 fish, 3 male swordtail, 5 female swordtail and 3 that are about 1/2 inch long at most, transparent fish that look like swordtail, but I'm not sure what they are.  
How can I tell if my female are pregnant?  I have had aquariums most of my life but have never dealt with swordtails.  These came from an outdoor pond and the biggest one is 2 1/2 inches long.  How many can I keep in the tank at one time and what other kinds of fish can I introduce that will get along with them?  The tank did not come with lighting or lids but I have not had a problem with them jumping out and I have a clip on desk lamp on the side of the tank.  I have a thermometer in the tank and watch the temp. every day, no problems.  The water has been clear and I've noticed no problems other than today.  They have started to "bunch" together at the top of the tank on one end or the other except for the small transparent fish, they stay mostly at the bottom.  Is this signs of something wrong?  If I send you a picture of the smaller ones can you tell me what they are?  Thank you for all your help.  I love my fish and want to keep them in the best conditions and health that I can.

Answer
Hello Sonya,

Swordtails come in every color of the rainbow, and can be really neat pets.  They can and will jump out of a tank, as will most fish if threatened, so I would strongly advise in getting a lid with a light, as a clip on light is really dangerous.

Females will be really fat when they are about to give birth.  Generally, if you have lots of cover in the tank, many will survive on their own.  Keep the 1 fish per gallon rule if they are about the size of your thumb.  Not including the sword part of their tails.  Any community fish will be okay with swords.  No cichlids, unless you don't want the swords anymore, as they will be eaten.  Mollies, guppies, tetras, platies, loaches, corys, rasboras, barbs, as long as you buy a bunch of them, otherwise they will get aggressive.  That should help fill it out.  

What type of filtration system do you have?  Over the back filter, or undergravel?  I didn't notice it, but for a tank that size, you will need at least 2 whisper 40's or 1 60.  Though two 40's would be better.


What temp do you keep your tank at?  It should be around 72-78 degrees.  Do you have airstones in it?  What are the ammonia, nitrite and nitrate levels?

Ideally, 0 ammonia, 0 nitrite and between 20 and 40ppm of nitrate.  Anything outside that, you will need to do water changes.  They should be done anyway, at least 20% every 2 or 3 weeks, depending on how many fish you have.  

I hope this has helped.  If you have any further questions, feel free to ask.  Don't forget to rate this.  

Sincerely,

Adrian