Q. The two angelfish I bought are a mated pair and have already laid their first hatch of eggs. About 50 fry survived. I tried feeding liquid food for the fry because I didn’t have time to hatch brine shrimp eggs. I put half of the fry in a 5-by-7-inch nursery in the same aquarium. A day later, all of the fry in the nursery were dead. The rest of the fry disappeared a few days later. The angelfish just laid another batch. Any suggestions for keeping them alive?
A. I’ll assume your fish are Pterophyllum scalare, the hobby staple. In this case, it really doesn’t matter what species you have because the following could be applied to any of them. Immediately after your angelfish finish spawning, you have two choices: leave the eggs with the adults or remove them for artificial incubation. Removing the eggs for artificial incubation means you’re going to play angelfish parent for the brood. If you want fry from the effort, it is easier to remove the egg-bearing structure (Amazon sword plant leaf, piece of water-logged wood or perhaps even the aquarium heater) than wait for the larvae to hatch. Once the larvae hatch, good angelfish parents will move them on a regular basis, which makes it more difficult to find and remove them. Also, there is some risk in siphoning very young fish larvae.
Let’s assume you are going to remove the eggs. Carefully separate the leaf, lift the piece of wood or unplug the aquarium heater the eggs are attached to and — while keeping the eggs underwater — place it in a smaller tank inside the aquarium housing the adults. It seems like you already have some practice with this part; just be sure to use something a little larger next time. (Actually, a 5-gallon glass aquarium floating in the aquarium containing the adults makes a fine nursery aquarium for the first week or so.)
Next, add some circulation, preferably in the form of an air stone operating vigorously enough to the keep a strong flow of water over the eggs. I also suggest adding enough methylene blue to significantly darken the water to prevent fungus from affecting the viable eggs.
The eggs will hatch in about two to three days, depending on the temperature. At that point, start making small, daily water changes in the floating aquarium to dilute the concentration of methylene blue; the larvae are not in any danger from fungus once they have hatched. Replace the water removed from the floating tank with water from the aquarium housing the adults, then top off that aquarium with fresh, dechlorinated tap water. The reason for all this water changing is that fresh tap water, even suitably conditioned, can be hard on the larvae.
Depending on the temperature, the larvae will use up their yolk in about five to six days and slowly begin to swim in the water column. By this point, you will have to make the necessary arrangements for feeding them. Newly hatched brine shrimp nauplii are perhaps the easiest and best food for newly free-swimming angelfish fry; swimming movements of the shrimp elicit feeding responses from the fry. Keep up with the daily water changes in the floating 5-gallon aquarium — still with water from the aquarium containing the adults. As you may have noticed, we’ve not started talking about filtration in the fry aquarium.
After about a week, and depending on how many fry you have, the floating aquarium may start to look a little crowded. At this point, it becomes necessary to set up a fry rearing aquarium; consider something around 15 to 25 gallons. When you set it up, fill it with water from the aquarium containing the adults to avoid any drastic changes in water chemistry that might stress the fry. As for filtration, the easiest method is to use a small box filter with the lid removed, so it can’t trap any of the fry inside. Again, continue regular water changes. You probably don’t need to do daily water changes, but that time will come. When the fry start to look like little angelfish and appear to “fill” the aquarium with their numbers, increase the water change schedule to daily. Otherwise, the juvenile angelfish may not develop properly. The most common side effects of poor water quality brought on by crowded conditions are short, stubby fins and curled gill covers.
As the fry grow, increase the amount of brine shrimp nauplii, and add in some other foods such as crushed flakes. You’ll also have to gradually increase the amount and frequency of the water changes, as well as clean the filter more frequently.
There is, of course, the other choice of leaving the eggs with the adults. Unfortunately, the aquaristic dream of watching a pair of angelfish herding their free-swimming young through the aquarium is seldom easy to arrange. Many times, tankmates prove too distracting for the pair — while they are seeing off an intruder, other fish in the aquarium make an opportunistic meal of the brood. Also, power filters can consume some or all of the fry. Even something as simple as turning the aquarium light off at night can cause free-swimming fry to panic. They disperse throughout the aquarium, then fall prey to the other fish. Of course, the angelfish pair may eat the eggs or fry themselves. While I’m a big fan of leaving the eggs with the adults, as I really do enjoy watching the brooding behavior, you’re most likely going to have to intervene if surviving fry are what you want. Good luck!