We have to be sure of certain facts:
As you get more experienced you will be able to merely glance at a fish to know its health, but obvious signs of illness to look for are:
Were the breeders in good condition after winter? If not it is too late to get them into breeding condition now.
Have you been feeding your fish live food since the start of spring?
Some other possible problems are:
We know goldfish get into breeding condition because of two triggers:
If you know your Goldfish are old enough to spawn, are in excellent health and conditions, are being fed live food or Repashy's Super Food, but the males don't develop tubercles and the female doesn't plump up with eggs, not enough natural light may be the cause.
This is seldom a problem with fish kept outdoors, even when the pond is quite shaded. It can be a problem with fish kept indoors.
It appears that the quality of the light is the problem, not the length of time the aquarium is lit.
Many breeders condition their fish outdoors, and then bring them indoors for breeding. Fish kept outdoors tend to spawn more readily than those kept indoors throughout the year.
If fish are in excellent condition, I have found it takes about three weeks for them to get into breeding condition once they have been moved outside.
If you suspect the female may have dropped her eggs, which would be indicated by the fish looking a lot slimmer, separate the fish for two weeks and feed them heavily with live food before trying again.
If Goldfish have been conditioned properly in the autumn, they will spawn multiple times in a season. Depending on temperature the interval can be as short as 6 days between spawns.
I tend to put them back together after no more than 14 days to avoid the female dropping her eggs prematurely.
If you are fairly sure the female hasn’t dropped her eggs, try a 25% water change in the afternoon. Keep doing this daily to see if it has the desired affect.
This is especially effective if the water temperatures are starting to get close to 80o F (27o C) when Goldfish start to lose interest in spawning.