Water chemistry: Zebera danios are very tolerant of water conditions and temperature. For breeding purposes, we will go with a PH of 6.6 – 6.8, temperature of 78-82 degrees F.
Sexing Zebrafish: Zebra fish are easy to sex if you know what to look for. The males are more streamlined in appearance that the females and the females have a more compressed looking body, not to mention the extra girth that they have at their abdomen when loaded with eggs after conditioning. Take a look at the picture at the top left of this article. The Zebra in the picture on top is a male. The one below is a female. Study the shape of these two fish for a while and you’ll get it. Piece of cake!
Selecting and conditioning the breeders: Place about a dozen mature (about the size of 1 1/2 inches) Zebrafish in a 10 gallon or larger aquarium. Make the PH 7.0 or neutral at this point and temperature at 72-74 degrees F.(We will lower the PH and raise the temperature when we are ready to breed them.)
For conditioning, feed them a variety of frozen and flake food 3-5 times a day until you see that the females load up with eggs and can surely tell males from females. This should take 2-3 weeks.
Setting up the breeding tank: For breeding purposes we will need a 5 1/2 gallon tank, 25 watt submersible heater, air stone supplied with air from a vibrator pump (we won’t set up the air stone until the fish have laid eggs) and enough marbles to place on the bottom of the tank to a depth of 2 1/2 inches deep across the whole tank bed.
Fill the 5 1/2 gallon tank with a water line about 2 – 2 1/2 inches higher than the marble substrate. Set the PH at 6.6 with a water temperature of 78 degrees F. Keep it there!
Now we will get these baby’s to breed! Since Zebra fish breed in schools, select two or three trios of breeders, 2 males to one egg rich female. Having this ratio of males to females will ensure the fertilization of the eggs and stimulate the breeding process by males and females ready to spawn turning on the other breeders to spawn.
Once in the breeding tank if properly conditioned, the fish should breed within a few days. If they don’t, raise the temperature a few degrees to 80 degrees F and change 5% of the water. Wait another day, change another 5% of the water and raise the temperature to 82 degrees. The third day and there after just do the 5% water change.
Keep feeding them 4-5 times a day until they spawn.
The mating process: Once the fish are in breeding mode, the whole school spawns! The eggs are dropped by the females and the males fertilize them as they drop. Where do they drop? Into the marbles baby! Since Zebrafish will consume there on eggs while breeding, the marbles and the low water line are there to prevent them from doing so. The eggs will drop down through the marbles, bouncing their way down to the bottom of the tank off the marbles where the adult breeders can’t get them.
You have eggs, now what? Once they start breeding it only takes an hour or so for the females to noticeably look thin and streamlined due to dropping their eggs. No rush to pull the breeders out for a few hours, the eggs are protected by the layer of marbles.
Once you are satisfied that the fish are done breeding and the females have no more eggs, net the breeders out and place them back into the conditioning tank, place an airstone in the tank set to slow bubble and 2 drops per gallon of methlene blue or acraflavin fungicide.
It will take about 10 days for the eggs to hatch and fry to become free swimming. They will find there way through the marbles on their own so just watch and wait. When you see them swimming around, add 1/2 quart of water a day of same quality and temperature to the tank to a normal 5 1/2 gallon water level. This will take a few days. When you reach the right water level, add a sponge filter. Change no more than 5% water a day to keep things fresh.
Feeding the fry: For a few days after the fry become free swimming, they won’t need to be fed. They are supplied by nature with an egg sack of which they derive nourishment for a few days to get a head start in life. When the egg sack in the belly region disappears, it’s dinner time!
Zebra Danio fry are too small to eat any kind of commercial fish food, there mouths are too small. Then what do they eat? Microscopic live organisms or Infusoria. You can buy Infusoria tablets at your aquarium shop. You just drop a tablet in the tank and in a few hours, your tank will be infested with live microscopic live fish food for the fry. I would pop a few of these tabs in the tank while the fry still have their egg sacks. Buy the time they are ready to eat, they got food! Another thing you could do is place a 2×2 inch piece of lettuce in the tank at the egg sack stage. This will also produce live food for the fry. In about two weeks time they will be ready to eat live or frozen baby brine shrimp and fine flake food.
Raising the fry: Wait about a month after the free swimming stage, then transfer them into a 20 gallon rearing tank. Feed them everything!