Hi, I have a betta fish. 
Those fish are great! They're small so you don't need a big aquarium and they have such beautiful colors!
I agree, they also dont need much food so they are low maintenance (unlike my wife).
Ha! Bettas are also known as Siamese fighting fish! Hopefully also unlike your wife!!
Siamese fighting fish? Can you tell me more about this? 
These fish are extremely territorial! They have extremely high levels of aggression toward each other. That's why they're always kept alone in their bowls.
I see, perhaps they might serve better as food than pets. Would you agree?
Maybe so! Betta owners even have to be careful when trying to breed their fish! The male and female can only share their space for a very short time, or they kill each other. Ha! 
Thats is rather shocking! I wonder what evolutionary purpose such aggression may have served.
5.5 in) in the Akar betta ("B. akarensis").
Bettas are anabantoids, which means they can breathe atmospheric air using a unique organ called the labyrinth. This accounts for their ability to thrive in low-oxygen water conditions that would kill most other fish, such as rice paddies, slow-moving streams, drainage ditches, and large puddles.
The bettas exhibit two kinds of spawning behaviour: some build bubble nests, such as "B. splendens", while others are mouthbrooders, such
Siamese fighting fish
The Siamese fighting fish ("Betta splendens"), also known as the betta, is a popular fish in the aquarium trade. Bettas are a member of the gourami family and are known to be highly territorial. Males in particular are prone to high levels of aggression and will attack each other if housed in the same tank. If there is no means of escape, this will usually result in the death of one or both of the fish. Female bettas can also become territorial towards each other