Macropodus opercularis, the Paradisefish

Macropodus opercularis (Paradisefish). Don't reduce this magnificent fish to a "Paradise Gourami." This is the "Paradisefish," period! It was the first tropical fish (not a goldfish) to reach Europe, exported to France in 1869 from Canton, where it had long been a traditional fish for garden pools. Kept like goldfish in glass vases in unheated European drawing-rooms, Paradisefish survived and even spawned, before the aquarium hobby really got under way. And this is still a good way to keep them, isolated in an unheated but planted aquarium that is kept at room temperatures. My experience has been that they aren't trustworthy in a community, but Dr. Thomas Seehaus disagrees with this general reputation in his article on Macropodus opercularis: even if you don't read German, his photos of spawning are worth a look. Certainly M. opercularis need no heater; they are comfortable even when water temperature dips below 60^o. Males will scrap fiercely with each other, once they've reached adult size. And females kept with a male are going to need some extra space and pretty dense plant cover. I had one male who lived solo for a long while in a rectangular two-gallon glass vase with only a single small potted Anubias and some Water Sprite at the surface, with half an inch of gravel to encourage bacterial nitrification and regular 50% water changes.
 
You do have to keep Macropodus covered with a glass lid at all times. Like many fish from weedy waters, they have learned that often the only way out of a constricted tangle of leaves and twigs is a good jump over the top. At my place, that's a poor gamble: Carpetfish!
 
This fish, kept in aquarium strains and called  the "colorful rabbit" in China, has a large natural range that extends from Indochina and the Malay peninsula in the far south,  and western Taiwan, where it's the "Taiwanese Paradise Fish" in a shrinking habitat, to Korea. From Korea, admirers introduced it into Japan about 1914. An inadvertent release from a garden pond during a flood in 1917 established M. opercularis in the wetlands of Niigata prefecture in Japan, where Takashi Amano noticed them when he was a boy. Doubtless it must also be human intervention that carried these strictly freshwater fish to the Ryukyu Islands and to Okinawa. These islands weren't connected with the mainland even during the deepest marine regression at the height of the Ice Age.
 
So, knowing they have such a wide natural distribution, you're not going to be surprised that there is a continuum of variation in wild populations of Macropodus opercularis. Besides the richly-colored usual version, there is a blond aquarium version with a strong blue cast, owing to its genetically-suppressed melanin cells and erythrocytes. Those are the black- and red color-bearing cells in the skin. The suppressed red coloration still gets evoked in a kind of negative way, since the ventral fins in the blond variant lack the handsome red leading edge and tail markings and the body stripes are washed out. In these "blond" fishes the blue opercular eye-spot also lacks its red margin. Though they're often on the market and I've kept them myself, I don't see the esthetic value of this variant, as you can surmise.
 
There also exist very strongly melanistic populations of "Black Paradise Fish" that some people like to call "Macropodus opercularis concolor" and others "Macropodus spechtii," though they usually have to add that so-called "hybrids" with the usual coloration exist. Though M. opercularis concolor, as it was then called, was imported into Germany in the 1930s, the line has been diluted with outbreeding to the regular color form and selected for extravagant finnage. In these mongrel "concolor" types you can still see that the dark scales connecting the eye to the bold ocellated gill-spot are not suppressed; they are still represented by a strip of darkest scales that still leads to a smudge, all masked by the general melanism of this dark variant, which gives a black rim to every scale and black edges to the anal fin.
 
The wild form is the version of Paradisefish to seek out, in my opinion.  A wild population of Black Paradise Fish were discovered in the 1990s, during a survey of Hong Kong wetlands conducted by Prof. David Dudgeon. At first they were taken for examples of M. opercularis concolor, but in 2002 they were described as a new species, M. hongkongensis. I think they haven't appeared in the market yet, but Dr Dudgeon's brief article on M. hongkongensis is at the University of Hong Kong website. 
 
I also hear about a "new purple strain" that loses its color as it matures. I'm skeptical. Sounds like another dyed fish to me. In 2011 there came  into the German market through Aquarium Glaser a new, legitimate sport of M. opercularis, which loses all black coloration to display a red body with blue nape and fins in coloration rather like a 'Sunset' Gourami.
 
 
The Paradisefish is an ambush predator. In the still and densely weedy waters that Paradisefish come from, a predator could waste more energy than it was likely to gain, if it tried to pursue prey over any distance at all. So Macropodus opercularis lurks just under the water surface, perhaps waiting for an insect moving at the surface within striking distance. This is why it is content in such a small tank. Mature males are intensely territorial and can't be housed together: in fact when a large dark dominant male rushes at another, even though the other is safely housed behind a glass partition, the aggressive move can cause the subordinate male to turn pale and roll sideways in submission. Females can also compete vigorously, with head-to-tail broadside displays and menacing slow reciprocal circling. Escalating threat displays may culminate in shivering and sinking of both fishes in unison, with spread opercula. The dominant female darkens her colors. Submission displays include a sideways roll to expose the flank and, in more intense confrontation, a head-up pose.
 
In a weed-choked backwater, a nearby male may be quite invisible; I think this may be why part of a dominant male's courting and territorial repertory also involves breaking the water surface repeatedly with his nape. Loud splashes and ripples advertise his size and strength — and distract you from the tv. The ocellus or outlined eye-spot on the gill-cover (operculum) gave the fish its specific name, and whenever you see that a fish has evolved an opercular spot like a fierce eye, it's very likely that gill-flaring will be one of its aggressive moves. It surely is true in this case. All this elaborated ritual, by the way, is an effective way to minimize actual physical damage to males during pre-spawning competitions. In small tanks, where escape is impossible, signals get crossed and fish can be damaged. There's nothing "natural" about fishes actually fighting.
 
Warmer temperatures encourage spawning behavior. Spawning involves a bubble nest. I've noticed that you can keep a male for long periods with duckweed and floating water sprite overhead, and he won't be inspired to blow a single bubble. Then introduce a plant with a bladed leaf on a long leaf petiole — Amazon Sword would do if you didn't have a big Cryptocoryne — and watch him go to work. Try this for yourself. My suspicion is that rootless floating plants don't register to him as suitable anchors for a nest, and that a blade leaf on a long sturdy stalk represents a plant that's firmly anchored in the mud. There is survival value in his choice: a bubble nest in floating plants is at the mercy of a freshening current and could be swept away, whereas one fixed to the stems of a rooted plant offers a more stable center to his territory.
 
In Germany, Dr Thomas Seehaus has found M. opercularis to be no more aggressive than, say, dwarf cichlids, but his beautiful photos show you the rich tangle of rootlets and leaves his magnificent fish inhabit. Though very small fish, or guppies with flaglike tails are not suitable tankmates, he has found that Paradisefish scarcely pay attention to other species, as long as they are not in reproductive mode and the territory round the bubblenest isn't invaded. (I feel, conversely, that the dense tangle of a clearly-defined territory defuses some aggression.)
 
Thomas Seehaus has been consciously developing a breeding line of Paradisefish to be as much like wild-caught species as possible. Over the years he has kept an eye out for outstandingly beautiful and robust fish to breed with his own stock. Recently, with changed policies in Viet Nam, some wild-caught Macropodus from Vietnam have been imported to Germany, and Seehaus received a wild-caught pair from the neighborhood of Quong Nam in Da Nang Province. He describes the wild form as less stocky than his established aquarium strain, with a more consistently displayed tailfin and and an even blue background coloring that only broke into speckles on the breast area. His peaceful and somewhat lethargic Macropodus pair showed no mutual aggression. When the male was removed for a couple of weeks and then returned, the female recognized him, displayed for him, and the two spawned successfully the following day. He noted her pale breeding coloration. But you should follow the link to the site, at least to see what I'd consider the proper environment for Macropodus. Wiljo Jonsson's good spawning photos of a blond pair of Paradisefish are at Bsdman's site.  
 
All in all, Macropodus opercularis is a seriously under-rated fish. By the way, I'd be interested in finding a copy of David Dudgeon, Tropical Asian Streams: Zoobenthos and Ecology, Hong Kong U. Press, 1997, to read the account of M. opercularis there.