Paradise fish - Macropodus opercularis
The genus is spread all over the south-east Asia, it belongs to Belontiidae. They are burly, slender, strong and flank oblate fish. They have a short mouth with marked lips. The dorsal fin is equal or bigger than 
the anal fin. The first ray of the pectorals fin is very prolonged, sometimes it`s even forked. The middle, superior or inferior rays of the caudal fin can also be very prolonged. The lateral line is incomplete or it is absent completely. They are very resistant fish but only the youngsters are friendly. In general, the can hardly endure the presence of other species in the same aquarium. They eat both alive food, which they prefer, and dehydrated flakes. They prefer sunny aquariums or an aquarium with lot of light. It`s better to avoid introducing them in new aquariums or in much planted aquariums.
Macropodus opercularis are long body fish, with very oblate flanks especially in the back part of the body. 
The males can reach 8 cm, females are a little smaller but with a big abdominal are (especially after sexual grow). The colors of the body can change because the fish are restless, especially males when they feel the presence of another male from the same specie. When they are excited, the color of the body looks like this: a blue-shining green background with transversal red lines. When they spawn, the males have the head and abdominal area colored in velvety black, the fins are from blue to red with another nuance blue lines. The male is more colored than the female and its lips are more marked.
Macropodus opercularis are spread from Korea to China, Vietnam and Taiwan where they live in stagnant or slow flowing waters. They were first introduced in European aquariums in 1869 and their first reproduction in captivity has been realized by Carbonnier. First Alfred Gunter and Boulanger thought they are artificial created fish, but Kreienberg proved they are not. He observed that the Chinese don`t keep them in aquariums and don`t even sell them like other species (selected goldfish).
A variant of Macropodus opercularis is Macropodus opercularis concolor. They are easy to breed fish; the temperatures can vary from 15 to 30° C and the minimum temperature can be 10° C.
Macropodus opercularis concolor doesn`t have the transversal lines, the only difference is that Macropodus opercularis concolor becomes almost black in the reproduction period and its fins are very prolonged. Their reproduction involves the building of a bubble nest, a particularity of the family. The water level in the reproduction aquarium doesn`t matter because the eggs are very oleos and they remain in the nest under the supervision of the male. Their reproduction is very similar to Tricogaster trichopterus and you can find more information there.