Fish Pregnancy / Disease Question

Question
QUESTION: How can you tell if a fish is pregnant?

I have read all through the fish disease symptoms and I can not seem to find an exact match to a problem that my red Platy is having.  She looks like her scales are coming off on her side and her underbelly, the area looks like it could be silver and a little concave. It is not a large spot and it's happening only on one side of her.  She is not as active in the tank as she used to be.  I added a dalmation Molly to the tank about 1 month ago and she seems to be a bully (just to the red platy), could this be part of the problem? I stopped at Pet Smart and they told me to treat with Maracyn for 5 days.  She doesn't seem to be much better, but she doesn't seem worse either. None of my other 7 fish in the tank are sick. Do you have any suggestions?

ANSWER: Hi Kristen,
I keep many platies and what you are describing does not sound like pregnancy.  When a platy is pregnant, she will look like she hasnt pooped in a month.  The underside of her belly will be big and plump.  It will bulge all around the belly and not just 1 side.  Also, their activity level also doesnt decrease that much.  Maracyn is an anti-bacteria medication.  If her scales are coming off something could definitly be wrong.  Have you tested your water chemistry?  What are you ammonia, nitrite and nitrate levels?  Has she been eating? If she has just been floating or laying at the bottom of the tank she could be having swim bladder disease which can be treated by any antibacterial med.  Do water changes to reduce nitrate level to promote healing of the fish.
-Matt-

---------- FOLLOW-UP ----------

QUESTION: I just had the water checked 2 days prior to my email to you at Pet Smart. The ammonia level is great, however the PH was a little low. The color is starting to fade on her as well now.  She doesn't seem slow anymore, and is eating fine. I will change 50% of the water tonight. Is there a medication that you can recommend that would work better than Maracyn?

My question in regards to pregnancy was general.  Will all species of fish look like they have a bloated belly?

Thank you for all of your help!!!

Answer
Hi agian Kristen,
What about nitrite and nitrate?  I know a fellow aquarist who just recently had 4 fish die because nitrates are high.    All fish can adapt to your current pH and temperature of the water.  Your ph is probably fine for the fish.  However live-bearing fish such as platies prefer higher pH, but they can also do well and will adapt to a lower pH.  Only fish that are live-bearers will have a bloated belly.  Live-bearers such as Platies, Mollies, Endlers, Swordtails, and Guppies.  Other fish will lay eggs and will not look bloated.  Maracyn works well, and I recommend it.  If she is eating fine and is active agian, she is probably recovering.  It is up to you if you want to dose antibiotics or wait to see if she will fully recover on her own with her immune system.
-Matt-