Jealous angelfish?

[FroFro]

So when I purchased my first angel it was I'd like to say.... maybe two years old? Anyway, I've no idea how to sex angelfish and research has shown that they are hard to determine gender till they pair off with another angel. Along with the mature angel fish I purchased another smaller one, perhaps 2 to 2 1/2 inches in length now. I'd like to repeat, I have had these angel's for the same amount of time and they both get along, even for their size difference. They've been living together for months and I've never seen any fin nipping or chasing around the tank or wounds on either fish. I am aware that angel's are part of the cichlid family so they can be naturally aggressive, but are known to be of a more even temperament than other cichlids. Anyway.

My Uncle had the bright idea to buy another immature angelfish since part of his pair has died. When I "acquired" this new and young angel he seemed to be alright if a bit stressed out. He (or she, don't really know) was being constantly harassed by the older angel and forced to hide in a cave ornament inside the tank. I adopted the fish and have since placed him in my tank. He seemed to perk up pretty quickly as I have ample room and no other middle swimming fish other than my two existing angelfish. I took the precaution of removing my own angelfish from the tank while I rearranged two of the plants and one ornament to kind of screw up territory for them but keep it largely unchanged. I then returned the angels to the tank with the third and they have been getting along fine for a week, until now.

I have absolutely no idea what gender my angel's are, but my smaller gold one has always had a shine for the larger, so I'm assuming they are two different genders, even though my mature koi angel has no interest in return for the younger gold one. Now to my point. I also noticed the new angel likes to follow my larger one around the tank, no matter where it goes. I came home this evening to find a small part of the new angel's top fin bitten off. The area isn't aggravated or ragged but looks like a clean sort of snip as if someone took a pair of scissors to his fin. I have no sharp decorations and my filter intake has a sponge all around it since my corydora like to get stuck on it otherwise. The new angel still follows the larger around, but if the gold one goes near him he hides or goes to the other side of the tank for a few seconds before swimming back to the larger koi angel.

So is my gold one being territorial? Jealous? I've since removed the new angel from the tank until I can figure this out and how best to solve the behavioral issue. Do I need to have an even set of angel fish? Should I perhaps re-home the new angel? I've seen pictures and read different posts on other fish forums on how people can and do keep a few angels together successfully as long as the environment/care is right. I just want to know if their is a way I can perhaps solve this behavior before I just give up on keeping this little guy, but if its for the best I'll find him another home.

Yes my tank is cycled. Has been for a while.

36 gallon tall, three angelfish and 6 corydora catfish, various types.

Tested the parameters again two days ago, everything is coming back safe.

I feed them once every two days.

Tank is kept at 77 degrees with the odd 1 degree dip during the night.

 

[Byron]

You were extremely fortunate that your original two angelfish got along at all. I would assume either they are both female, or they are male/female and have "accepted" each other in the same territory. This does not always happen, in fact it is rare, so you are lucky there. When one wants a "pair," it is necessary to select a pair that have obviously accepted each other in the store tank. Even so, sometimes for reasons we do not know, bonded pairs will suddenly turn. But if they bond on their own, it is generally safer than putting any female in with any male and hoping it works, as it usually doesn't.

Adding a third angelfish now is a real risk and almost guaranteed to not work out, as I believe you are seeing. It would seem that the aggressor is the smaller of the original two, and this fish is most likely thus a male, the larger likely being a female. This would also explain why the added fish is trying to stay close to the larger (presumed female), whether the new fish is male or female. It has invaded the territory of the original regardless of gender and this is not going to last long before it is killed.

Now some biological background on this fish, Pterophyllum scalare, the common angelfish (in any of its man-made varieties). Angelfish in nature form smallish groups, and establish a distinct hierarchy. Males will form a territory, and if they pair off to spawn, other angelfish will not be tolerated within the territory. The larger the group in the aquarium, the better, up to a point; five is the minimum. And before someone jumps in to say it, sometimes four can work, rarely three or even two unless they bond, but less than five is risking things and rarely works long-term. This needs space however, at least a 4-foot tank like a 70/75g minimum for five, larger with more.

A 36g tall will not allow any territories aside from that of the dominant male, so please don't consider adding more angelfish. It simply will not work, and given the situation as you have set it out, I can guarantee this.

The corys are fine, but your new angelfish needs another home or it will not live long (if back in the 36g I mean). Feel free to ask if anything is unclear.

Byron.