i have just bought 2 silver mollies and 2 guppies for my tank. I introducted them yesterday and they seem to be doing fine. However, i am very interested in breeding them, but i have absolutely no idea whether they are M or F. I was going to get another 2 mollies 1 M & 1 F, and the same with the guppies, but i am not sure if my tank is too small. Thats why i wanna know how big they grow...

Guppies will grow to 2/2.5'' mollies a bit bigger at upto 4'' You can tell the sexes apart easily by their anal fins -males have a long 'tube'like fin whereas the females will have a fan like fin, its normally recomended that if u do keep mixed sex you have more females per male to avoid the females being harassed by the males constantly which can be stressfull.Mixed sex will breed quickly and easily so make sure you have enough room to take care of the fry.

Be sure to keep an eye on the fry when they come, as the parents may eat them if given the chance.

my guppies gave birth to fry, but sadly she eat all of them bar one, but now that is also dead due to the high temperatures we just had.

Euryale is correct, it is highly recomended that u buy a couple more female guppies and mollies, to stop your females getting sexed to death lol what a way to go