While angelfish will pair and become fiercely territorial as breeders, the short answer to this is yes. Angelfish pairs can be broken, swapped, and even put back together, but there are few important things you need to do to ensure the safety of your fish. You also need to understand what's happening with your angelfish and know the breeding cycle of both pairs you're trying to swap. We've had a lot of success at swapping angelfish mates by paying attention to the points below.
All's fair in love and war and angelfish
Attraction in angelfish is a fickle thing. There's no list of points to hit to force angelfish to pair up with each other. If you have a male and a female in a well-kept tank, odds are they are going to try to mate. On the flip side, you'll notice that pairs who have mated for months or years can suddenly fall out of favor with each other.
It's been proven that pheromones or other chemicals released by angelfish affect their behaviors, helping them recognize each other, affecting how they act socially, and coercing them into mating. That being said, the only way the average aquarist can manipulate pheromones is through water changes. Keep that in mind as we talk about how to swap mating pairs. For the ease of conversation, we'll be referring to pheromones and any other chemicals that may be released by angelfish as pheromones.
In a nutshell, to swap angelfish mates you need to do the following steps:
Wait 48 hours after you've removed a pair's spawn.
Do a large water change in both aquariums - between 60-80%
In some cases, especially if you're new to breeding and reading angelfish body signals, add a tank divider. Definitely have one on hand for each aquarium.
Swap the males just before lights out.
Feed their favorite foods as a distraction just before removing the divider.
Using water changes as a disruptor
You may have noticed that water changes are a trigger with your angelfish. A happy pair likes to spawn after a good-sized water change, to the point of clockwork. In our experience, pairs that are closer to their wild counterparts tend to fight, or "test" each other, after a sizeable water change. One can only conclude that the pheromone balance in the water has been thrown off, and these fish don't recognize each other anymore. After a day of tussling, these fish reaffirm their choice in mates and everything goes back to normal. What's really interesting about this is that the fish never lose sight of one another, so while they may be able to visually recognize their mate, the pheromones are the key trigger whether or not the other fish in the tank looks familiar.
Know your pair's mating cycle
Angelfish breeding cycles are fairly predictable. Some fish like to breed every 7-9 days, while others will regularly breed every 3 weeks. One thing that is common between all angelfish is the build-up toward the day they lay their eggs. The pair becomes very territorial and their tubes drop as they ready to lay. If you were to swap mates in the days prior to spawning, you'll end up with a dead angelfish as the "owner" of the tank is on a mission to defend their home. If you're thinking about swapping two pairs of partners, you need to ensure you're careful at reading your fish. We've found it's best to swap a pair around 48 hours after removing a spawn from the aquarium. If the fish breed on a Monday and you remove the eggs that day, then you should be swapping the mates that Wednesday.
Ideally, you would break apart a pair first, separating them for a few days after a spawn so that their hormones can settle without their partner's pheromones affecting them, but we've directly swapped pairs and kept an eye out for aggression.
Move the males
When defending their spawn, both males and females become territorial. You'll notice in larger aquariums that the female will play close-quarter defense, staying near her eggs or the spawning site, while the male provides long-distance air strikes as he dart attacks anything in the aquarium. When trying to swap mates, it's safer to swap the males of the pair and leave the female in an aquarium she knows and feels that she owns. Females tend to be smaller than males, which works well if she's the aggressor. It's easier to deal with a little bully rather than a big one.
Keep an eye on body language
There are a handful of things you need to be wary of, and if you see them, you need to separate your fish with a divider. Many of the issues below can be avoided by making sure you swap mates just before lights out.
Ripping attacks - Pecking and nipping will be normal, but when an angelfish bites and tries to tear with its head, they are trying to dish out some serious damage. An occasional bite like this is normal, as the new fish is "invading" its territory, but repeated, successive attacks means is a bad sign.
Darting attacks - When your angelfish flips on its side and goes for a high-speed ram, you've got a problem. This is a big attack. The angelfish is not trying to test a new mate, it's trying to kill the intruder.
Destroyed fins - So you went out for a bit when everything looked fine, and you came back to some torn fins. That's ok, it's your angelfish trying to sort things out. You should never see more than some minor nips or tears. If I had to give it a number, maybe 5-10% of the fish's overall fins being damaged. If you see major damage, like fins ripped off or dorsal fins cut in half, or large patches of scales ripped up, you missed some critical signs and need to add a divider immediately.
Hiding fish - If your new addition is hiding, that's ok. He probably is smart enough to know he doesn't want to fight. If you find that when you feed your fish, the other angelfish is attacking him and keeping him away from food, you have a situation you need to keep an eye on. Angelfish can bicker, but typically when food is added to the tank they call a truce on their fighting. An angelfish won't take longer than a day to come out of hiding when dealing with a new mate.
Rebound attacks - This is important, pay attention. The female may stop attacking the male, and the male could rebound and start attacking your female. A little aggression is fine, it means they're testing each other out, but keep an eye out for any of the above aggression factors as the male works to claim the aquarium.
Try a few different set-ups
Not every forced pairing will work out, but if you really want those specific angelfish to breed, try a change of scenery. Put them into a 48" long aquarium that's new to both of them, and treat them as you would normally. Angelfish tend to have a 36" area that they guard, so a tank of this size is ideal for letting your angelfish meet each other on their own accord.
Leave a comment, a question, or even a contradiction down below and we can learn together.
Andrei Vexler is an aquarist with over 20 years in the fish hobby. Having run a fish room with over 700 freshwater and saltwater aquariums, Andrei found his passion in South American cichlids, particularly Altum angelfish. Growing and wholesaling angels to the GTA and the surrounding area, he shares his years of experience in his blog for advanced aquarists.