How to tell if your marigold platy fish is pregnant and what to do?

Chances are if your female platy was kept in an aquarium with male platys the likelihood of her being pregnant is very high. The general rule for keeping both male & female live-bearers in the same tank is a ratio of 2-4 females per male. The reason for this (which you seem to be experiencing) is that the male will become very persistent and chase the females around. Keeping more than 1 female will help alleviate some stress in your aquarium. Both the male and female platy will try to eat the young fry once they are born so you may want to confine the female to a “floating nursery” until they are born. Once the fry are born, remove the female and place her back in the aquarium. From there you can keep the fry in nursery (or move them to another aquarium) until they are large enough not to be eaten.

A female guppy will develop what is known as a "gravid spot" when pregnant. It is triangular and located near the vent on the abdomen under the tail. It will get bigger and darker as she nears spawning. If she was skinny when you got her and she is that big now, she is pregnant. They are live bearers, so the fry (baby fish) will need cover (places to hide) or they will be eaten. It is best to separate them into grow out tanks.

She may have had too many babies developing and sacrificed some eggs in order to have the rest of them develop properly. I would not upset her now by removing the eggs. I suggest you leave her in the breeder box until she has the rest of the babies. Ignore the eggs on the bottom of the box, It is likely that they will not survive. But Platys have young all the time, so it is not such a problem. She will have live young soon.

On average, a platy female can spawn 20-50 fry (baby fish). The first spawning may be less. If she still appears bloated or round, she may still have fry to spawn. If no more appear after a day or two and she is back to "normal" size, then she can be returned to the main tank. The fry should remain in a grow out tank or they will likely be eaten.

You need only provide plenty of space, clean water and a quality flake or pelleted diet. Male goldfish will develop white dots on the fins and gills when ready to mate. He (they) may chase her around and bump her stomach to get her to spawn (lay eggs). When she is ready, she will seek out planted or quiet area of the tank and spawn. The males will then release sperm to fertilize the eggs. The eggs will need to be removed to a separate tank to prevent them from being eaten by the adults. The eggs will need to be kept at a certain temperature and in clean water until they hatch within a week's time. Afterwards, you will have MANY fish to care for and feed. This can quickly become an overwhelming task and should not be undertaken without serious forethought. You can read more about goldfish breeding here: http://thegoldfishtank.com/goldfish-care/breeding/goldfish-breeding-breed-goldfish/

Hard to say from your description whether she is pregnant or ill. You can tell male from female Mollies by looking in the area of the anus. A male Molly has a so-called gonopodium. The gestation period of a molly fish is about 60 days. Female mollies can store sperm for months and may fertilize eggs as often as every 30 days, even without a male in the tank. Mollies may release 10 to 60 live babies at a time. Here is an illustration of sexing Mollies (and other live bearers)(credit: Mwahahahaa) http://photobucket.com/gallery/user/Mwahahahaa/media/bWVkaWFJZDoyMDk0MTEzNw==/?ref=

She appears to have eggs given her girth. There are also some vertical bars on her side that indicate she may be ready to spawn. If possible, check underneath for a pronounced white dot. This is further proof that she is ready to spawn.