Betta fish are indeed territorial but that doesn't mean they're destined to live a solitary life, forever swimming alone in their tank. Although that may be your Betta's preference, you might enjoy having a tank inhabited by diverse species of marine creatures. The key is in knowing which is the best tank mates to pick for your Betta.
Territorial temperament of Betta fish
Although birds of the same feather flock together, the same is not true for Bettas. They are highly territorial and see others like them as rivals. So keeping two Betta males together in a tank - unless there's a divider to separate them - is never a good idea. Sometimes, even with a divider in between them, it's still not a good idea because they'll keep sparring with each other and end up stressing each other out.
In the wild, when two Bettas engage in a battle, there's always space for one of the Bettas to flee. Not so in a Betta fish tank. Male Bettas aren't very tolerant of the female of the species either, except when it's breeding time. And that's a very small window.
Female Bettas are pretty confrontational as well, but not as much as their male counterparts. It is possible to put female Bettas together in an aquarium, but you need to keep an eye on them initially. When two females are in the same tank, there's going to be a lot of bullying by the dominant one.
It's a better idea to put several females in the tank instead of just a couple. When there are several present, there will be some skirmishing at the start, but usually only until a hierarchy is established. Just keep a close watch. There are some females who are just too aggressive and don't like living with other Bettas.
The bad tank mates for Betta fish
You have to be very selective in deciding a companion for your Betta. Many species can be best mates for the Betta but there are many others that don't go well with them. As it is important to know which fish makes the best companion, it's equally important to understand the species that cannot exist with them.
One of them is Goldfish. They can grow to six inches long and create a terrible mess. They tend to generate more waste in comparison with other fish. They take the food from one side and discard from the other end. This crap (no pun intended) could be disastrous for the Betta. Also Gold fish survive in cold water while Bettas are tropical fish. Other non-candidates as Betta tank mates are fish that are a great deal larger or much smaller than the Betta.
Paradise fish male and female. Source
If you are thinking about Gourami and Paradise fish then stop right there. They are an absolute no-no. Firstly, though some Gouramis are dwarf, there are some that can be one foot long. This would not give adequate space to the Bettas. Secondly, both these species of fish build bubble nests that are similar to one another. This would only contribute to the aggression towards each other. So it is better to keep them away.
If you love your Betta fish and want to save them from enemies, then never think of keeping Angelfish. Many people think Betta fish might pose a threat to the Angelfish, but it is other way round. It's the Angelfish that can be dangerous for Betta fish. They are not only larger but can also nip away the beautiful fins of the Betta fish. Angelfish are known to grow as large as ten inches and require a bigger tank.
Fin nippers are aggressive, as they would show their dominance over others through fighting. Some Tetras species like Rosy and Serape Tetras, Danios, and Barb are fin nippers and that makes your Betta's beautiful flowing fins a prime target for them.
Serape Tetras are well-known as fin nippers. Source
On the other hand, Bettas can perceive fish with fancy fins such as male Guppies as rivals and go after their fins. You might want to also stay away from Mollies, as they would go to a great extent of bugging Bettas. In return Bettas would give them a good chase and even bully them if they come in their way.
So, if you really love your Betta fish then you need to be selective in your choice for their companionship as a slight mistake can have disastrous impact on their overall health. They can become irritable and even die.
What kinds of fish can live with Betta fish?
Corydoras, Platies, Plecos, Harlequin Rasboras, Dwarf Rasboras, Swordtails, and Tetras are some of the best tank mates for Betta fish. Some fish such as Corydoras, Neon Tetras, and Rasboras can live very well in small tanks but they are schooling fish and need to be kept in groups of more than five specimens to live happily. Neon Tetras and Rasboras are mid-tank fish, Corydoras are bottom feeders, so they and Betta will stay out of each others' ways that makes them the best tank mates for Betta.
Cory catfish – best tank mates for Betta
Fish don't have to be the only tank mates of your Betta. Bettas get along well with snails and shrimps. They're actually ideal companions for your Betta since they're slow moving and they're bottom dwellers. (Bettas don't like a lot of motion in the water.) An added benefit of having some ghost shrimps or a zebra snail in your tank is that they'll keep the bottom of the tank clean. Amano shrimps are also a good choice to keep your Betta tank free of algae.
Betta fish and ghost shrimps
Female Bettas are usually more accepting of other fish than are male Bettas. Again, it all depends on the individual Betta's personality as well as the size of the tank. If you provide enough space for the fish to have their own individual territory and lots of hiding places, you may be surprised at what some Bettas will accept as companions. Remember, it's all about territory.
You can't really tell how your Betta will react to a potential tank mate until you release the candidate into the water. It'll take a few days of close monitoring before you finally know. The newcomer will have to find his place in the tank and your Betta will decide whether he will tolerate the situation or not. There may be some initial bullying or skirmishing, but things may settle down. Or they may not. It's important to have an extra tank on hand as backup, in the event that your Betta doesn't feel hospitable. You need a home for the other fish.
Choosing tank mates for your Betta is an exercise that requires preparation, experimentation, and observation, but when you come up with the right mix, it will reward you with many hours of delight.