There is a group of fishes native to Asia that possess a form of lung.
Gouramis have evolved a type of lung called a labyrinth which enables them to breathe air in order to enable them to survive in poorly oxygenated water and to make a nest of bubbles in which they nurture their eggs.
In general, the Gouramis that we keep in our freshwater tropical aquariums are very peaceful in nature. They mix well with other fishes provided that the aquarium is not overcrowded but, in my experience, they do have a tendency to nip at the tails of fishes that have elaborate or elongated fins.
Origins of Gouramis
Gouramis are native to Asia, ranging from Pakistan in the west all the way to the Malay Archipelago in the east and northeasterly to Korea.
The Gouramis generally kept in aquariums are very slender in width but with an oval body which is roughly twice as long as it is deep.
Many Gouramis have elongated “feelers” in front of their pectoral fins. These feelers have a wide range of movement and the Gourami can control the movement of each feeler independently.
Since Gouramis have evolved a form of lung called a labyrinth, they can take in gulps of air from above the surface of the water. This enables them to thrive in still water that other fishes would find survival difficult, as it is the movement of the surface of the water that removes carbon dioxide from the water and enriches the oxygen.
Gouramis as a community fish
My experience of Gouramis in a mixed aquarium informs me that they are a graceful and beautiful addition to most aquariums. Gouramis do, however, have a tendency to nip at the tails of fishes with elongated or elaborate finnage so it’s best to avoid keeping them with the various fantail Guppies, Swordtails and similarly elaborate fishes.
The male Gourami is territorial when he is ready to mate whereas the females are comfortable as a small shoal so you could quite reasonably keep one male and several female Gouramis in the same tank.
The Gourami family includes the Betta Splendens (Siamese Fighting Fish) of which the male, which should never be in a tank with another, similar male, has very elaborate finnage and would have a miserable existence if kept with other Gouramis.
Gouramis are extremely fascinating to watch. They tend to occupy the area of the tank from the top to the middle but will venture to all parts of the tank on occasion.
Much of the time, Gouramis tend to move slowly and gradually but they can dart around the tank with great speed when the mood takes them.
How do Gouramis breed?
Gouramis are otherwise known as labyrinth bubble-nesters which provides an excellent clue as to how they breed. Before you can breed Gouramis, however, first you need to know whether or not you have a male and female fish.
In general, the male of the species is a slightly smaller fish than a female of the same age. Of course, if there is a significant age difference then this observation may reveal nothing of value.
The male Gourami tends to have a slimmer, less rounded body whilst the female has a more rounded body which is greater in girth. This more rounded body is usually particularly obvious around the belly area between the pectoral and anal fins.
The most obvious way to differentiate between the male and female Gourami, however, is to observe the dorsal fin. In the image above, the female Gourami is to the left, She has a modest, rounded dorsal fin. Compare this with the male on the right. His dorsal fin is larger, longer and ends with a point at the tip. Note that the differences in young Gouramis may not be obvious so it may be that you must wait for the fishes to become more mature before you can determine their sex with certainty.
The male Gourami is generally the dominant fish and it will be the male Gourami who ensures that the eggs hatch into fry.
The male Gourami tends to become much darker when it is time to breed. The belly of the female Gourami becomes much larger as it is filled with eggs.
Breeding tank for Gouramis
You should prepare a tank of around 20 gallons in size with mature, still water. Remember that in nature, Gouramis thrive in still water. Ensure that there is plenty of floating vegetation in the tank but further ensure that there is clear water surface where the Gouramis can take their gulps of air.
If the tank contains an air block and/or a filter then turn them off or the Gouramis simply will not breed, as they require the water surface to be still.
The male Gourami will start to build a nest of bubbles into which he wants the female to lay her eggs.
Once he has built a substantial nest he will then entice the female to lay her eggs by performing a ritual dance which includes wrapping his body around hers and rolling her so that she deposits her eggs into his nest.
The male will collect any eggs that are not contained in the nest and place them into the nest. The female can lay up to 200 eggs but she may lay only a dozen or could lay more than 200.
Once the female has laid her eggs she should be removed carefully from the breeding tank because the male then becomes very protective of his nest and may well kill the female. He will certainly chase her away from his nest so she will have a miserable time until she is removed back to the community tank.
During the time it takes the eggs to hatch, the male will tend to the nest and protect the eggs.
Once the eggs start to hatch (usually after a couple of days) then it is wise carefully to remove the male, as he may devour the fry as they hatch.
At this point, you can switch the filter back on.
It will take the fry a few days to be capable of swimming freely so it may be prudent not to switch on an air block (unless it is contained in an under-gravel filter tube).
Assuming that the breeding tank is a mature tank with a good collection of mature plants then the natural cycle of life in the tank will have produced the infusoria (a collective term for the microorganisms that help with the decomposition of plant material) that the fry (baby fishes) will consume once they are hatched. If in doubt, add infusoria at least daily for the first week after hatching.
After around one week you may wish to add some small, live brine shrimp, as the fry will probably have grown sufficiently to catch and consume them.
Should your Gouramis have a special diet for breeding?
This is a much-discussed topic amongst aquarists. My personal belief is that all fishes should enjoy a rich and varied diet at all times including flake food, vegetable matter, live food and dried, live food. The fishes will themselves determine what they prefer to eat. In a community tank, fishes should be fed, as a general rule, once or twice each day and any food placed in the tank should be consumed within three minutes. The only exception to this is live food which the fishes will hunt down and devour.
Having decomposing food lying at the bottom of the tank is bad for the tank and bad for the fishes and, if you have catfish in the tank, they are not there as vacuum cleaners and should be treated with the same thoughtfulness as your other fishes.
If your fish are always maintained in the best possible condition then there is no reason whatsoever why any fishes should require a special diet to induce them to breed. You could make a point of feeding more than the usual amount of live food if you make any changes at all.