[EDIT: Though this blog focuses on tangs, these methods can be applied to many other fish that are aggressive toward others of their same or similar species.]
Many aquarists have successfully added a young captive bred Biota tang to their tanks that have existing older, wild tangs. This Biota blog will help you learn some useful tips and tricks for keeping multiple tangs together.
Why are tangs aggressive toward conspecifics and similar species?
Some people tend to think of only carnivores as being aggressive, but tangs and other herbivores can be aggressive to protect their territory. Many tang species are considered to be “peaceful,” while some are “aggressive,” but even peaceful tang species can be aggressive toward other tangs, and sometimes even toward other herbivores like blennies if they feel their territory is too small or if their food supply is perceived to be limited. Tangs also tend to be more aggressive toward their own or similar species.
How do tangs fight?
Most fish species will use their teeth to fight, so new tang owners might be surprised to see their fighting tangs line up side by side. Instead of biting, tangs typically use a sharp spine (scalpel) at the base of the tail (caudal peduncle) to slap and puncture their opponent. If you see your tang swim next to another fish while flaring all its fins and darting quickly back and forth, this is aggressive posturing.
top and bottom left: various tang species' caudal peduncle weapons
bottom right: a tang with injuries
How to introduce new fish to a tank that already has fish
We strongly recommend introducing any new fish to a tank using an acclimation box; this is particularly important for smaller fish. This allows the new fish and your existing fish to get to know each other in safety. More importantly, using an acclimation box also lets you keep a close eye on the fish so you know it is getting food and isn't swept away by pumps or filtration while it's tired from its long journey. Make sure your acclimation box is large enough to accommodate your new fish comfortably for several weeks. Place it in an area that gets plenty of flow so the water inside doesn't become stagnant. Provide lightweight hiding places like PVC or macroalgae in the box. Observe the fish in the box for at least a week, and if the fish aren't acting aggressively toward it, try releasing the fish.
All fish are individuals, and like other animals, have unique personalities. If at any point your fish fight, ideally you'd catch the aggressor and isolate it in the acclimation box to allow the other fish to establish territories and gain strength. If you can't catch the aggressor, it's OK to put the bullied fish back into the acclimation box until signs of aggression are gone. With particularly aggressive fish, you may need to repeat these steps. Have a back up plan in place in case you need to permanently isolate or re-home an aggressive fish.
Tang groups should be kept in a very large tank
Your tank should be at least 6 feet long if you want to keep multiple tangs together. Very young tangs can be kept in a smaller tank together temporarily during quarantine or grow-out, but they grow quickly. Adult tang groups should ideally be housed in the largest aquarium possible. A tang that feels crowded may act out aggressively.
Have a lot of rock arranged with a lot of hiding places
The aquascape of your tank is important. Tangs are strong swimmers and need plenty of open space, but they also need lots of live rock with caves and crevices to feel safe.
A well-fed tang is a happy, peaceful tang. In the wild tangs graze constantly. If they sense a lack of food, they will be more likely to fight. It can be a fine balance between feeding enough to make tangs happy and controlling organic waste in the tank. Especially when tangs are first introduced together, feed multiple stations of "grazing" type foods like nori seaweed sheets on clips or Easy Reefs Masstick at opposite ends of the tank and replace as often as possible.
Add tangs at the same time
Your best bet is to add an odd number of tangs to the same tank at the same time. Two tangs will only have each other to fight with, but three tangs will disperse their aggression three ways. It’s better if you can find tangs that are already used to being together. Biota captive bred tangs are housed in our facility together with others of their species and tend to acclimate together better than tangs that have been housed alone. Younger tangs also tend to get along better than tangs introduced together as large adults. Though it's more likely for young fish that are already familiar with each other to get along in a new environment, there is still a possibility of aggression, so have an acclimation box on hand to separate the aggressor temporarily while the new fish get used to their surroundings and new hierarchy.
Turn out the lights
When you open the shipping box, you don't want to shock your new fish with bright lighting. Turn off your aquarium lights and make your room as dark as possible. Adding new fish into a dark tank will also encourage the fish to rest instead of fight. Keep the lights off for the rest of the day and allow them to come on in the morning. Aquarium professionals use red light in dark dedicated acclimation rooms because fish don't see red light. You can use a red light at home or a red flashlight to view your tank at night.
Add tangs in order of size and each species’ aggression level
If possible, add tangs according to size. The smallest specimens should be added to the tank before larger ones. If you’re adding different species together in one tank, consider their aggression level. For example, a Blue Tang is considered to be peaceful while a purple tang is considered to be semi-aggressive, and a clown tang is aggressive. Add the most peaceful species first. Some individuals of the same species can be more or less aggressive depending on their personality and life experiences. If you can't follow these rules, be sure to use an acclimation box to introduce new fish! Adding multiple tangs in odd numbers helps break up aggression if you already have established, older tangs in the tank.
It is usually easier to add tangs together when they have a different body shape, color, and are a different genus. For example, adding a captive bred Yellow Tang and a captive bred Blue Tang together at the same time is likely to be successful.
Aquarists use creative ways to distract their "bully" tangs. 3D printed "decoy" tangs, a mirror or a picture of a tang taped to the side of the tank can attract a bully to help keep it away from a new tang. Moving the rockwork around and breaking up a bully's territory can also help when adding a new fish.
If you have any questions about adding a captive bred Biota tang to your aquarium, please feel free to reach out to our support team.