Hi, I'm new here and this is my first post, so pleease bear with me. My son brought home a goldfish from a carnival over the summer and we kept it in one of those small desktop aquariums for months and for his birthday, we decided to get him a nice 10 gallon setup with some more fish. That was about a month or so ago.
We had the goldfish, some sword tails and a pleco in the tank, plus a snail and spongebob.
I noticed the goldfish was floating all weird yesterday and figured he'd lived his goldfish life to the fullest and I was prepared for his upcoming funeral. Only he evidently wasn't a HE because this morning, I found about 10-15 babies in the tank.
I'm totally not prepared for grandmotherhood. How is this possible?
Short answer is, "it isn't". Goldfish are egglayers, not livebearers, and cannot reproduce with a single individual.
Swordtails are livebearers--the color of the tail has nothing to do with the sex. The shape does.
The female--with a normal tail--is on top. The male, with the long extension on the tail, is on the bottom in both of these photos.
You can leave the fry be and see if they survive--the parents might cannibalise them or the goldfish may eat them--or you can buy a little net breeding trap to put the fry in to raise them. Your call.
Unfortunately, your setup remains less than ideal in quite a few ways.
Most people don't realise it, but common goldfish (comets, carnival goldfish, etc) grow over a foot long and can live over 20 years (so he is/was nowhere the end of his natural life span.) The 10-gallon tank MIGHT be big enough for the goldfish, alone, by the time he's grown. The pleco, also, will more than fill that tank all by himself--they also reach well over a foot, I've seen several at nearly 18 inches. Also, Plecos and goldfish both are extremely messy fish, and produce huge amounts of waste even at fairly small sizes.
The swords are the only fish, sizewise, that are approrpiate for a 10-gallon.
Also, there are habitat and dietary issues at play here--goldfish and swordtails need practically opposite things when it comes to their water. (The plecos are more adaptable.) Goldfish need COLD water--they thrive at room temperature, can surive freezing temperatures, and begin to get stressed out when the water reaches the high 70's or low 80's. Swordtails are tropical fish--they need the tank in the 74-78 range, which during winter in most places, means it needs a heater. They both can tolerate similar Ph, although the goldfish like it a little higher (above 7.5, even up on to 8) when the swordtails like it just above neutral (7) to maybe 7.5. It's not the worst Ph mismatch possible--tetras, who like it down in the 6's, would be a much worse match with goldfish--but it's still not fantastic.
Also, diet--goldfish are extremely prone to constipation (quite likely why your fish was floating upside down, actually)--and need a diet nearly entirely made up of plant matter. Tropicals need more protein in their diet. If you're feeding "tropical flake" the goldfish will have issues, including the aforementioned constipation, and if you're feeding "goldfish flake" the swords won't do as well.
BTW, if the goldfish is still floating oddly, try feeding him a cooked, shelled, smushed up green pea. That's one of the best cures for constipation in fish, there's a lot of plant/roughage bulk in the peas and it helps clear them out.
I would honeslty advise you to reconsider your tank--returning the swords and pleco might be the easiest option--and to start shopping at a good, quality local fish store who'll give you the proper advice on a tank--wherever you've been going doesn't seem to know their facts if they sold you the setup and the fish they did. Best of luck with whatever you end up doing.
