I categorized them with labyrinth fish. I have already written a section on bettas, but if you'd like to, by all means, go ahead! Here is my section:
Betta (Betta Splendens)
Native to: Thailand and surrounding countries.
Ease of care: Easy, males should be kept alone.
Length: 2.5 in. (6 cm.)
Minimum Tank Size: 5 gallons for a single male or female, 20+ gallons for a group of females.
Temp: 72 - 78 Fo (22 - 25 Co)
Ph: 6.5 to 7.5, can be kept in harder water with Indian Almond leaves.
Aggression: Males are very aggressive towards each other, Females are semi-aggressive, if you keep multiple, you must have 4 or more.
Is it pronounced Bay-tah or Bet-ah? (I think it's Bay-tah, but that's not important). The betta has exploded in popularity over the years, going from just veiltailed, red or blue varieties to hundreds of color morphs, including mustard gas, black samurai, koi, and galaxy, and a wide selection of fin types, including half-moon, plakat, crowntail, double tail, and elephant ear. There are even giant bettas, which can reach up to half a foot! The possibilities are endless!
Bettas tend to be very aggressive, especially the males. For that reason, males should not be kept with other males, and they are best kept alone. A good target size for a single-betta tank is 5 gallons. Females can be kept together, provided the tank is large enough, and has enough cover. The tank should be planted, and the lower the flow, the better. The tank should be at least 20 gallons for a group of 4-6, with peaceful cleanup fish, such as Corydoras or Otocinculus, and peaceful schooling fish, such as Cardinal Tetras. Do not house bettas with fin-nipping fish. These fish need easy access to the surface to breathe atmospheric air, and they like to have floating plants.
Male bettas can be identified by their pelvic (lower) fin. The males will have a longer pelvic fin that extends past the tail fin, and females with have shorter pelvic fins that do not extend past the tail. Females tend to be a bit more plump than the males, and they do not build bubble nests. Do not keep bettas with shrimp, because they will eat babies and sometimes even the adults!
I think for the sake of not confusing readers too much, we should put the silver halfbeak in, but with the oddballs. Otherwise, we should stick to the 5 common ones: Guppies, Endlers, Mollies, Swordtails, and Platies, as well as maybe the American Flagfish.