As your fantail goldfish mature, they'll want to make fantail goldfish of their own. Be aware that, when this happy time comes, you’ll need to help the spawning process along. Nutrition and environment are important. While fantail goldfish are hardy, they need the ideal spawning conditions.
Ideal Egg-Laying Conditions
Your fantail goldfish love, love, love cold water, so keep their water colder than for other species -- about 70 degrees F during the day and 50 degrees F at night is ideal. To induce spawning, you’ll gradually raise the temperature of the water in the tank over several weeks, imitating a change of seasons. Change about 20 percent of the water once a day, and make sure to raise the temperature slightly to put them in the mood for some lovin’.
Feed your fantail fish a varied diet, using high-quality food, such as live or frozen brine shrimp or worms. Your fantail goldfish also enjoy fish food with veggies.
Separate your female fish from their male companions, putting them into another tank for a few weeks. Even for fish, absence makes the heart grow fonder. When you reintroduce the females to the males, they’ll be much more interested in each other -- “Hey, remember me, Felix? You're Felicity, right? I, uh, I like your fantail.”
When it’s time for your fantail goldfish to start spawning, add spawning mops to the aquarium. These enable the sticky li’l fish eggs to adhere to them when baby-making time has come. You’ll find these at the fish store, ready to take out of the package and drop into your aquarium.
Female Goldfish Role
The female fantails have the simpler role -- they simply begin depositing their eggs, which stick to almost any surface inside the aquarium. A larger fantail goldfish is capable of laying about 1,000 baby eggs in one spawn, but only a fraction of the eggs will survive. The mama fish can release several batches of eggs, but the first one usually produces the strongest eggs. Once the mama fantail has laid her eggs and the male has fertilized them, look for the clear eggs -- these are the ones that will become the small fry.
Male Goldfish Role
This is the fun part: Once you’ve reintroduced the soon-to-be mama fantail goldfish back into their community, watch the male goldfish as they respond. They’ll act like typical males do, chasing the females all over the tank. And they'll butt up against the females' bellies. As soon as the females release their eggs, the males catch their breath -- seriously, though, fish don’t breathe -- and they spray something called “milt” over the eggs, fertilizing them.
The Human Protector
Yep, you’re gonna take on a protective role with the little newborn babies. Adult fantail goldfish have a rather bloodthirsty habit -- they like to eat baby goldfish, even their own. They also like to eat the eggs. Right after the eggs have been fertilized, take the spawning mops out of the aquarium, rinse them in clean water and put the mops into a 20 gallon tank with water no deeper than 6 inches. The little egglets love cool water, so keep the water temperature at about 70 degrees F.
It’s important for you to remove the fertilized eggs that have taken on a cloudy appearance. These little ones won’t grow up into baby fantail goldfish and, if they are allowed to stay in the aquarium, will attract all sorts of unattractive, unwelcome fungi. To prevent this, you’ll need to remove these dead eggs. The ones that don't turn cloudy will hatch in about three to four days as long as the temperature stays constant.
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