A Red Siamese Fighting Fish

The Siamese fighting fish (Betta splendens), also known as the Betta and simply as the fighter, is a popular species of freshwater aquarium fish. The name is derived from Ikan Bettah, taken from a local dialect of Thailand (Siam). 

Betta is pronounced /ˈbɛtə/. The wild ancestors of this fish are native to the rice paddies of Thailand, peninsular Malaysia and Cambodia and are called pla-kad or trey krem ("fighting fish") in Thai.

Siamese fighting fish have upturned mouths and are primarily carnivorous surface feeders, although some vegetable matter may be eaten. In the wild, they feed on zooplankton including crustaceans and the larvae of mosquitoes and other insects, such as flies, crickets, or grasshoppers.  Fish who feed on a wide range of foods live longer, have richer colors, and heal fin damage more quickly.

For reproduction the male betta will flare his gills, twist his body, and spread his fins, if interested in the female.

The female will darken in color, then curve her body back and forth. Males build bubble nests of various sizes and thicknesses at the surface of the water. The act of spawning itself is called a "nuptial embrace", for the male wraps his body around the female; around 10-41 eggs are released during each embrace, until the female is exhausted of eggs.

The male, in his turn, releases milt into the water, and fertilization takes place externally. During and after spawning, the male uses his mouth to retrieve sinking eggs and deposit them in the bubble nest (during mating the female sometimes assists her partner, but more often she will simply devour all the eggs that she manages to catch). Once the female has released all of her eggs, she is chased away from the male's territory, as it is likely that she'll eat the eggs due to hunger.

Henceforth, the eggs remain in the male's care. He carefully keeps them in his bubble nest, making sure none fall to the bottom, and repairing the bubble nest as needed. Incubation lasts for 24–36 hours, and the newly-hatched larvae remain in the nest for the next 2–3 days, until their yolk sacs are fully absorbed. Afterwards the fry leave the nest and the free-swimming stage begins.
A Red Siamese Fighting Fish in an Aquarium - Pictures