Clownfish are among the most popular saltwater fish in home aquariums. They're colourful, hardy and don't require large tanks or expensive setups that most complex reef tanks demand. Breeding clownfish and raising fry (baby fish) can be an extraordinarily difficult task, however, that requires precise concentration and a great amount of care. When your clownfish mate and lay eggs in your tank, typically in clusters along rocks or coral, prepare to take care of them when they hatch.
Fill the 10-gallon aquarium with water (there's no need for substrate or decor or a filter) and then mix in 3 cups of marine salt. This is the hatchling tank and will be used to contain the fry immediately after they're born.
Measure the specific gravity of the hatchling tank's water with the hydrometer, which will tell you how salty it is. Dunk the hydrometer under the water's surface until it fills, then place it on a flat surface. A needle in the hydrometer will point to the specific gravity of the water. Ideally, you will want around 0.0020 ppt (parts per trillion). If the specific gravity is too low, then add more salt. Conversely, if it's too high, then dilute it with fresh water.
Cut the airline tubing into three equal sections, each 3 feet long.
Attach an air stone to the end of one section of the tubing. The air stone will simply squeeze on. When it's on tightly, place it in the hatchling tank's water.
Connect the other end of the same tubing from Step 4 to the output of the external air pump. This is where air is expelled.
Plug the external air pump into a power outlet. Air should then be forced through the airline tubing and out of the air stone, circulating the water.
Attach the compact fluorescent light to the tank. Most of these lights come with a clamp that attaches to the plastic trimming at the top of the tank.
Order live rotifers, which are tiny aquatic organisms that the fry can eat, and rotifer diet from an online retailer like Reed-Mariculture. Baby clownfish will not eat frozen food or flake food, only living rotifers for the first week or so of their lives.
Fill a bucket with water and mix in salt. Measure the salt using the hydrometer as outlined in the section above until you've achieved a specific gravity of around 0.0017 to 0.0020 ppt.
Push an air stone onto one end of the second section of plastic tubing and place it in the bucket of saltwater.
Attach the other end of the airline tubing from Step 3 to the output of an external air pump. The output is where air is expelled. Plug the external air pump into a power outlet to begin circulating the water in the bucket.
Add the live rotifers and rotifer diet once they arrive. Allow them to proliferate for around 3 days until the water turns green.
Locate the eggs in your aquarium. Hopefully, the clownfish have laid them on a rock that can be easily removed from the tank. Once they turn from pinkish to silver, they are ready to be transferred to the hatchling tank.
Submerge a plastic bag in your clownfish aquarium and scoop up the rock containing the eggs, making sure to keep as much water in the bag as possible.
Lift the bag of water and rock out of the aquarium and carefully place it into the hatchling tank. It is absolutely imperative that the eggs not come into contact with air.
Remove the bag from around the rock with the eggs and wait for the fry to hatch.
Scoop up some of the water from the rotifer bucket using a coffee filter. This will capture rotifers while filtering out the green water.
Submerge the coffee filter into your hatchling tank's water and shake it, removing all of the rotifers. They should begin swimming around the tank, and the healthy fry should dart after them.
Repeat Steps 1 and 2 daily for about a week. Make sure to scoop out any fry that do not survive this first week, as their carcases can cause an ammonia spike in the tank.
Cut the top off of a 2-liter soda bottle and fill it with water and marine salt. Use the hydrometer as outlined in Step 2 of Section 1 above to make sure the water's specific gravity is between 0.0017 and 0.0020 ppt. This will be your brine shrimp hatchery. The clownfish fry will be able to eat live baby brine shrimp after about a week.
Attach the last air stone to one end of the last section of airline tubing and place the other end of the tubing to the output of the final external air pump. The output is where the air is expelled. Place the air stone in the water and plug the external air pump into a power outlet to begin circulating the water.
Add the brine shrimp eggs and wait for about 24 to 48 hours for them to hatch.
Remove the brine shrimp from the soda bottle using a turkey baster, being careful not to collect any of the brown egg casings they leave behind.
Inject the baby brine into the hatchling tank, as well as some rotifers. Slowly ween the fry off of rotifers for about 3 days, and then completely feed them brine. Continue feeding them brine and repeating the necessary steps to hatch more for about 2 to 3 weeks, when the babies should be big enough to be moved into a larger aquarium and begin eating normal flake and frozen food.
If the clownfish laid eggs on a piece of coral or a rock too big to remove without exposing it to air, then wait for the fry to hatch and then transfer them one by one into the hatchling tank using a turkey baster to capture them.
Be prepared for the fact that most of your clownfish fry, particularly the first few times you attempt to raise them, will probably die. Even professional breeders lose about 10 per cent of their babies with each batch.