The best time to hand spawn is when the breeders are in the act of spawning, and there are problems such as:
If the breeders look ready but are reluctant to spawn, (the more exotic the variety the more likely this will occur), then you can test just how ready they are.
Net the female carefully. Her struggles or the slightest finger pressure on her abdomen will cause a spurt of amber eggs into the net.
Net the male and perform the same test. This time a small amount of white milt will be expelled.
If the breeders pass the tests, you can safely hand spawn your goldfish.
You will need a small shallow container such as a soup dish. The size will depend on the size of the female and the number of eggs you expect to collect. If your female is say an 8 inch Comet, expect several thousand eggs.
If the container is too small, there will be too many eggs clumped together and they will not get enough oxygen.
Prepare the container to catch the eggs by filling it with water from the breeder’s pool or aquarium.
Place spawning mops or plants in the container to catch the eggs making sure the sides and bottom are covered.
Net the male.
You can leave the male in the net. Apply gentle pressure to his abdomen as can be seen in the picture below. A small puff of milt should be seen. Repeat this several times, applying gentle pressure to both sides.
You only need a few puffs of milt.
The small volume of water in the container will mean the fertilization rate will be high.
Move the net or fish around the container to distribute the milt evenly. Return the male to his container.
Stir the water again to help distribute the milt.
Net the female. Note her distended abdomen swollen with ova. If she is ready to spawn, the eggs will squirt out with her slightest movements.
The female can’t be left in the net like the male because the eggs attach themselves to the first thing they touch.
Lift the female from the net using your hands, refer to the picture. Keep fingers away from her anal pore unless you want to hold your hand in heated water for 4 days until the eggs that attach to your fingers hatch.
Her slightest struggle will spray eggs into the container. Move her around to distribute the eggs evenly. Remember, you aren’t milking a salmon. Be very gentle. Even a few hundred fertile eggs will make the effort worthwhile. It isn’t worth the risk to try and strip every last egg from the female.
Once you have collected enough eggs, let them water harden for 30 minutes. Remove the spawning mops or plants from the container, flush them in clean aged water of the same temperature and place them in the aquarium or container you will be using to hatch the eggs.
If several hundred eggs are expelled before you can remove the female from the net, you can always cut the material from the net frame and leave it in the hand spawning container to be fertilized, then move it to the hatching aquarium.
If a large number of eggs attach themselves to the hand spawning container, you can either place it in the aquarium you will use to hatch the eggs, or if the container is something like a small plastic aquarium, just flush the eggs with clean aged water after a few hours and then place a heater and air stone in it.
Warning: I've viewed some YouTube videos to see if there was anything suitable to use on this page, as a video is far superior to images.
I was horrified at what I saw. DO NOT use these videos as examples of how to hand spawn goldfish. If I find something suitable, I will provide a link or create a video myself.
With your eggs now sitting in your aquarium awaiting hatching, start reading the page on raising your goldfish fry.