The Angelfish Is Among 4 Of The Most Aggressive Freshwater Fish
If you are interested in starting an aquarium, you should know some of the most aggressive fish you can buy. All fish can be passive or aggressive at times,but some fish are predatory in nature, like the Barracuda, which would make them a more aggressive species than say, a Guppy or Molly.
One of the most aggressive freshwater fish is without a doubt, the Red-Bellied Piranha. Though they can make a great addition to your tank, they will eat any fish that is smaller and they can grow to 12 inches, so putting them in a cross-species tank is a no-no.
Next is the stunning Siamese Fighting Fish or what is commonly known as the Betta Fish. Some would argue that this is the most aggressive freshwater fish as you can`t put two males together, or they will fight to the death. Even when breeding these fish, you must separate them shortly after breeding or they too, will fight.
Female Bettas are duller in color and usually don`t show this aggressive behavior and can live in a community tank though I have had females that were aggressive to other fish and had to be taken out of the tank so my advice would be to watch her closely, to see how she is acting after adding her to the tank. You should also be able to put just one male in a community tank with other species but there cannot be a female Betta in there with him.
Then there is the Angelfish. These Cichlids can be extremely aggressive but they usually co-exist with Tetras quite well. They should not be put with Guppies, however, as the Guppy will fin-nip the Angelfish. The best thing to do is only put fish that are the same size or bigger as the Angelfish, to avoid their aggressiveness. If you introduce a new fish to your tank that has an Angelfish, do it after feeding time and under a low-light condition. as per www.articlecity.com
Last is the Paradise Fish and the males are very aggressive, but once they have established a hierarchy, it usually subsides. Females will usually not display this aggressive behavior. For more info, you can visit: www.learnfreshwateraquariums.com
Image source en.wikipedia.
Breeding Siamese Fighting Fish - News

Next is the stunning Siamese Fighting Fish or what is commonly known as the Betta Fish. Some would argue that this is the most aggressive freshwater fish as you can`t put two males together, or they will fight to the death. Even when breeding these
Siamese Fighting Fish Care And Forum
The name Siamese Fighting Fish came from when they were first used by gamblers in the Far East. They would put two males together and watch them fight, often to the death of one, for money. Splendens are one of a few species of male fish that will not tolerate any other males in their vicinity. The origins of their aggression are unknown, but it is believed by some to be a natural territorial behaviour. However, through persistent captive breeding, this aggression has been increased to an un-natural level. Siamese Fighting Fish originate from the paddy fields, gullies and streams of South East Asia, and are found mainly in Thailand, Borneo and South Vietnam. They thrive in stagnant ponds and slow-moving water. Because of their Labyrinth, a special “lung”, they can survive in water with very little oxygen by coming to the surface periodically to breathe. In fact, they have been known to drown if they cannot get to the surface! Not all Siamese Fighting Fish are super-aggressive. Much depends on the way they are bred. If they are bred in a community the aggression is much less than if they are bred in separate jars. The aggression factor is further increased if they are not allowed to see any other Siamese Fighting Fish while growing to adult. “Carding”, (placing card between each jar to obscure the view of other fish), is very common amongst breeders of Siamese Fighting Fish for this very purpose, although many breeders will give the excuse that by constantly “flaring” at each other, they get tired. (Flaring is the term used to describe the spreading of gill covers and fins in a display of aggression.) Personally I have successfully bred splendens in a community with very little sign of trouble. I consider this to be successful if they can co-exist as a community until 6 months old, when the males are very noticeable. As juveniles, they will flare at each other, but I have not had any fatalities or even serious aggression displayed. Usually one of the males will quickly submit and swim away, doing a headstand to show his submission. Once this happens, the winning male flares and swims away too. At 6 months old, I take the males out and give them their own space, but still allow them to see other Siamese Fighting Fish. Females of the species are usually much more placid, and don’t carry nearly as much finnage. They can exist happily in a community indefinitely, either in groups of 6 or more females, or with one male and a group of females.
Breeding Siamese Fighting Fish - Bookshelf
Siamese Fighting Fish
The Betta Handbook
The Siamese fighting fish is one of the first fish you see in a pet store and one of the ... People breed them for fun or profit and throw away the excess, ...Siamese Fighting Fish
Pocket guide to the care and maintenance of aquarium fish
Avoid baby fish or small neons as bettas will eat them. Related species: Gouramis, paradise fish. Breeding: To breed Siamese fighting fish, ...A complete introduction to breeding aquarium fishes
The Siamese Fighting Fish ... of breeding for lovely colors, they try to produce males that will fight bitterly when placed with another of their own sex. ...Everyday Knowledge Directory
Breeding Bettas " MX Bettas - about Siamese Fighting Fish
Breeding Bettas is very rewarding. Discover some of the mistakes I made at my first attempt at breeding Bettas ... The Story of My First Two Siamese Fighting Fish Spawns ...
Breeding The Siamese Fighting Fish
Breeding the Siamese Fighter Fish is because of it's roots not very difficult, but definitely very interesting. The Fish is used to live in less than ...
MX Bettas - about Siamese Fighting Fish
Siamese Fighting Fish are very easy to keep as a pet and make a fantastic gift idea. Siamese Fighting Fish are also known as Betta Splendens, Betta ...
Breeding Bettas (Siamese Fighting Fish)
Breeding Bettas (Siamese Fighting Fish) Breeding Betta splendens can be quite a rewarding ... To condition the pair for breeding it is best to raise the water ...
Do-It-Yourself/Breed siamese fighting fish - Wikibooks, open ...
Breeding Siamese Fighting Fish. The system of betta fish is based upon aggression ... be serious consequences with fighting between fish, especially if the defeated ...