So what's the deal with tangs? How do I keep them together? Why are they so aggressive and difficult to keep sometimes? It's a common discussion point. Some may dissent with what I have to share but I've never had less than three tanks running at a time, up to 7, and have been in the hobby ~15 years with 2 of them spent working for an LFS running their saltwater fish dept largely, for what it's worth.
Root of Tang Aggression:
Understand that from a tangs point of view, more herbivores means less algae. They've evolved to defend their patch of algae and territory very hard because they may starve if someone else comes in and takes it over. It's literally life or death for them. Angels and other herbivores are occasionally ousted but tangs in particular are often in direct competition for food and will be heckled heavily. The only herbivore that is tolerated (sometimes) is foxface. This is because they're venomous. Even still I've seen tangs stress them to death literally.
Tangs are often most aggressive to members of the same species in home aquaria and species in the same genus. When not schooling, they often protect a patch of rock from other fish, often other tangs, particularly tangs of the same species. (It is much more likely that they will compete for food since their diet is identical)
Tangs are also more likely to be aggressive in the home aquaria because they are stressed and in smaller quarters. Even the best hobbyists have questionable environments compared to their natural homes in the ocean. Fish that swim several miles each day such as many acanthurus tangs (particularly PBT, Achilles, etc) feel cramped and as with any organism that is stressed, they can respond to this by "acting out" (aggression).
The author keeps quite a few tangs in his own aquarium as you can see in the 2 photos below.
What Does Tang Aggression Look Like?
Tangs are purpose built for eating algae and defending said food source. They're equipped with at least one scalpel near the base of the tail for "swiping" other fish. This is where the name "surgeonfish" came from. These can do a lot of damage and leave serious lascerations. When adding or mixing tangs, be on the lookout for aggression and know when to implement "Plan B". Constant chasing, nipping, and swiping is not a good sign and unlikely to stop. As you'll read later, some species hold grudges forever and others let bygones be bygones on occasion. It's your job as the hobbyist to know when to intervene. Occasional chasing, flaring fins, circling each other, or swiping motions that are clearly a dominance display rather than a true attempt at puncturing the other fish should be noted but are common in a tank mixed with territorial herbivores.
With all of this in mind, your existing tangs are not going to be welcoming.
The degree of aggression the new tangs receive can be curbed by:
1) Keep them very very well fed. Keep enough nori in there that by the end of the day it is gone but they have access to it for most of the day. This will make them feel like they need to compete less, but it's no guarantee.
2) Re-arrange rockwork. This can be successful because the tang feels like they are no longer in their territory temporarily and may hesitate to be as aggressive as otherwise.
3) Add multiple tangs at a time. Tangs can take some serious abuse, but 3 on 1 new addition is terrible odds. It may work but the new fish will be very stressed and possibly stabbed several times. Even if only one new tang heckled the new tang it would not be a fair fight - a fat established and possibly more aggressive species targeting a fish that has been through heck getting to you and as such has a weak immune system, is thinner presumably because it hasn't eaten as it should, and is very stressed. More tangs will increase distraction and will break up aggression considerably, providing you don't have a tang that singles one of the newcomers out. Powder blue are notorious for picking a grudge and taking it to their grave. Other aggressive species often simmer down in a weeks time. If the fish makes it that long things should get better, presuming they don't succumb to ich or other parasites.
4) Use acclimation boxes. This shields the newcomer from attacks from other fish and gets them used to seeing the new fish. It also allows the new fish to adjust a bit so that it is better able to defend itself and know its surroundings better.
5) Mirrors placed in the corner of the tank. For a very aggressive tang, sometimes a mirror placed in the corners will keep the fish flashing and attacking itself rather than harassing a new addition. I've personally never done this but have heard of some limited success.
6) Removal of the problem fish and a re-introduction later. This can work because the tank pecking order is disrupted. The fish will be confused by the change and work out their own new pecking order and be less concerned with harassing the newcomers. Upon reintroduction some few days or months later, assumedly the new fish will not be the tank boss and will not be as territorial as a result (since it is not his territory now - yet)
7) A combination of these ideas. To hedge your bets, mixing strategies may well be worth the effort.
8) If you are planning to add tangs of the same genus, definitely add more than one. I frequently break the rules with tangs. One tank has a PBT and Achilles tang together, another has a PBT, Achilles, and goldrim together. I even have a pair of achilles together (do NOT try this at home). They get along great. This wasn't easy and some fish had to be moved around and they were added simultaneously most of the time. I've always kept purple, yellow, and sailfins as a trio. Again, adding at the same time. They've always gotten along well. I've done this for 12 years with more than three test groups in various tanks on various occasions.
Adding a yellow to an established purple for instance is likely to end in the death of the yellow. Adding an Achilles to a PBT is often murder.
Notice the 2 Achilles tangs, PBT, and Goldrim together in these two photos.
9) Adding tangs of larger OR smaller size. There is different logic to this theory, both is probably valid. Add larger less aggressive tangs than your most aggressive tang to intimidate it. Again some may not be intimidated... particularly PBT.
Adding smaller tangs may make sense because the existing tang may see them as LESS of a threat for dominance in the pecking order (but still a threat to its food sources...)
Many people have different opinions but the only steadfast rule I follow is not to add tangs of the same exact size unless I am adding them in groups.
Conclusion:
Understand that none of this is fool proof. Powder blue tangs in particular are notorious for holding a permanent grudge. Months of time apart will not work if they have a "personal vendetta" to destroy a fish-- not always a tang, either.
Sohal tangs IME are not nearly as aggressive as people make them out to be. I hypothesize that a few people had terror sohal tangs and their stories keep getting repeated by other members and shared with others. As such, they get a worse rep than they deserve because of the same stories being told by several reefers. Honestly I don't even rank sohal tangs in the top 5 most aggressive tangs, although it is on my list because I've not owned all tangs
My list is this: (I'm only ranking tangs I've actually had experience with). This is just an opinion after having several of each species over the years in multiple tanks.
1) Powder Blue
2) Powder Brown
3) Sohal (increasingly nasty with size)
4) Clown (increasingly nasty with size)
5) Achilles (some are docile but the nasty are up there with PBT)
6) Purple
7) Yellow
8) Goldrim/ White Cheek
9) Scopas
10) Gem
11) Kole (increasingly nasty with size)
12) Sailfin
13) Atlantic blue
14) Desjardini Sailfin
15) Hippo & YB Hippo
16) Tomini Tang
17) Chevron
18) Orange Shoulder
19) Convict Tang
20) Blonde Naso
21) Naso
A lot of variance exists between species, this is just my experience and observations over the years with other peers and kin I interact with or see them and their tanks frequently.
I hope this is helpful.
