Betta fish, also known as Siamese fighting fish, are very common sights in fish bowls and home aquariums. Often found in small cups on pet store shelves, the Betta fish has become an extremely popular pet for its hardiness and ease of care. Like many fish, Bettas have developed a variety of physical adaptations that help them survive.
Betta fish contain a unique organ in their heads called a labyrinth organ. These special organs allow the fish to extract oxygen from air at the water's surface instead of extracting it from the water itself using gills. Fry (baby fish) typically have primitive gills, but they fade as the fish develop, replaced by the labyrinth organ.
The Betta fish can survive in very harsh, low-oxygen environments thanks to its labyrinth organ. Being able to breathe in oxygen from the surface means that not only can the fish survive in poor water conditions, such as near drainage pipes or puddles that receive practically no aeration, but it can even survive out of water for a fairly substantial amount of time.
The most commonly kept Betta, the Betta splendens, rarely grows more than 2 1/2 inches in length, and because of its combination of small size and low-oxygen tolerance, it can survive in very tiny spaces. This adaptation accounts for the fish often being found in cups or small fish bowls. In the wild, they can survive in puddles and tiny streams.
The male Betta fish is a very territorial animal. It is aggressive toward many other fish, particularly other male Betta fish. The male Betta can typically only be kept with female Betta fish and medium-sized tropical fish like gouramis and angelfish.
The Betta fish reproduces using bubblenests. Bubblenests are mats of bubbles blown by the males that float on the surface of the water, often anchored to a floating plant or piece of wood. The female Betta releases eggs, which the male fertilizes, and the female then mouthbroods them, taking them into her mouth, swishing them about, and then depositing them into the bubblenest where they will develop into eventual fry.