The paradise fish or paradise gouramis (Macropodus opercularis), are small freshwater labyrinth fish found in ditches and paddy fields in East Asia, ranging from the Korean Peninsula to Northern Vietnam.
Paradise gouramis were one of the first ornamental fishes available to western aquarium keepers, having been imported to Europe as early as the 1800s. These small fish (adults are typically about 4" (10cm)) are ideal lone inhabitants of aquariums, being physically robust, somewhat colorful and more alert/behaviorally interesting than goldfish. The paradise fish is one of the more aggressive members of its family, by being more aggressive than the blue gourami. Yet they are far less aggressive than the rarely kept Combtail.
Paradise Fish are fairly combative, harassing and attacking each other as well as potentially killing small fish. In the wild, they are predators, eating insects, invertebrates and fish fry. The popularity of this species has waned in recent decades as much more colorful (and often, less pugnacious) species of gouramis have become widely available to hobbyists. This species is one of the few fish that can change its color (lighter or darker) in response to stimuli.
Paradise gouramis are tolerant of virtually any water conditions, surviving in cool and warm waters alike. They can be kept in outdoor ponds, or even the simplest of unheated aquariums. They will accept virtually any food, but should be given a reasonably high-protein diet (as opposed to vegetable-based foods of the sort sold for goldfish.)
Male paradise fish should be kept apart, since they will fight aggressively by locking jaws. Male can be kept with females; females may also be kept together in groups. A tank that includes paradise fish should be at least 2.5 gallons in size for a single male or 20-30 gallons for a community tank. The tank should be well planted and covered; bogwood and rockwork may be included. Paradise Fish are often aggressive thus tankmates must be chosen with care. Suitable tankmates include giant danios,large tetras,most smaller catfishes and even some of the less aggressive cichlids,such as firemouth cichlids.They can hold their own against most South American cichlid species of a similar size, that aren't overly aggressive. Slow moving or long finned fish such as fancy goldfish and freshwater angelfish are likely to be attacked, bettas and gouramis may also be victimized due to their resemblance to paradise fish. Male paradise fish may also attempt to court female bettas and gouramis. Small fish less than 3cm are likely to be consumed. Males are particularly aggressive and should not be kept with slow fish or fish with long, flowing finnage which is commonly shredded by the territorial paradise. In a community tank, male Paradise fish fight other paradises, as well as any other fish for dominance. Paradise fish will often fight with other fish for dominance, particularly other aggressive, robust fish, such as cichlids, gouramis, and even flying foxes. They therefore should not be housed with any other fish which may attempt to challenge them, because this leads to fighting.
As is typical of most bettas and gouramis, spawning involves a male building a bubble nest (a floating mat of saliva-coated air bubbles, often incorporating plant matter) and attracting a female to it. If the female accepts the male's advances, the fish will 'embrace' in open water, releasing both eggs and sperm into the water. The male gathers the fertilized eggs after each embrace, spitting them up into the bubble nest. After spawning, the male has no further use for the female and may violently attack her (and any other fish that approaches the nest.) Once the fry hatch and have begun to swim freely, the male is best removed and the fry raised on infusoria or newly hatched brine shrimp.
There is an albino form of Macropodus opercularis available. Many aquarist authorities consider this form to be less aggressive than the wild type.