By advising someone to check water levels is giving someone the thought that something could be wrong. And I was not being rude at all with my reply and I know very well what this forum is all about. I was just stating the fact that your answer came off as if it is impossible to breed tetras and that the fish were sick. Instead of jumping ahead of ourselves and stating that it could be dropsy why not ask if there are any signs or symptoms present first? It could be nothing at all.
Do I know for sure that she is holding? No, heck for all I know it could be a male but for the death of potential argument I am respectively waking away from this thread, to the OP, best of luck.
IMO you could throw a PM to Andy Sager and find out a little more information about the breeding of tetras.
Thanks for the nod butterfly
but I believe all the points that I would have made, have been made. Only livebearing fish can be pregnant so at best, this fish is "carrying eggs" or the term is gravid.
This is some other info to keep in mind:
If this was a disease, typically, when a fish is sick with bloat or dropsey, they will not be acting "normal" but I have to say that based on the pics, this is not a sick fish. I will say. tho, that routine checks of the water chemistry should be done anyway so if any fish starts to change in appearance and you do not do routine checks of the water, you should do so to confirm that water chemistry is not an issue.
As for type, I believe the poster who said these are cardinals may be correct. The main difference between Cardinals and Neons is that cardinals are more elongated than Neons and their red stripe goes from gill to tail as opposed to a Neon whose red stripe is only halfway through the body. These look to me, from the pictures, as elongated fish with full red stripes so they would be cardinals in my book. (I am using the characteristics of wild caught fish so if these are tanks raised, this method might not be acurate anymore. I would then be using the body shape comparison.)
As for breeding: Cardinals, Neons and all egg laying fish can be holding eggs without breeding for their entire mature lifetime so if you are not trying to breed them, don't be concerned about it. HOWEVER, Cardinals have been bred commercially for quite some time, just as Neons have, in the Far East so they are not impossible to breed. In fact, many breeders from around the world have bred them. The common themes with breeding them are soft water and a low PH. If you are trying to breed these fish and they are in a community tank that differ from these water parameters, I'd use a separate tank as the lower PH levels might harm some of your other fish (I say this precautously as I don't know what other fish you have in the tank.)
As for sexing Cardinals, it's usually only confirmed when the female fills up with eggs. Young/ immature females look exactly like males so when you are trying to breed them, you want to make sure you pair a "fat one" with a "skinny one" if you hope to have any success.
If you have any further questions regarding breeding these fish, feel free to PM me.