If you are breeding small species of gourami, use a tank that is 18-24 inches long.
If you are breeding bigger gouramis, use tanks that are 30 inches +, depending on the species. Some gouramis can reach 2 feet in length and need to be bred in large ponds.
They like soft slightly acidic water (GH below 100ppm and preferably below 50ppm) and a pH between 6.5 & 7.0. However, most captive bred fishes will breed in water that is a bit harder and has a slightly higher pH, but it's best to try and replicate their natural environment, which is soft slightly acidic water.
The water temperature should be around 26-30C for breeding, and the optimum temperature for rearing the babies is 28C. Have a cover on the tank and insulate the back and sides with polystyrene foam to help keep the tank warm.
The aquarium should have a layer of gravel or sand on the bottom, lots of floating plants, an air operated sponge filter, heater if required, and a coverglass. You need minimal surface disturbance for the males to build a bubblenest. If there is too much movement on the surface, the nest will be torn apart or the male simply won't build one. The water height should be about 8-12 inches for small species and 12-18 inches for medium size species. Floating plants help to provide a calmer surface and provide somewhere for the bubblenest to be built.
The male builds a bubblenest when he is ready to breed. He entices a female to the nest where she lays a few eggs and he fertilises them. Then the male (and sometimes the female) collect up the eggs and put them in the bubblenest to develop. After the female has shed all her eggs, she is driven away from the nest and the male guards the nest and developing eggs. Depending on the species, the size of the aquarium, and the number of plants in the tank, the female can sometimes be left with the male. However, if the tank is small or the male is being aggressive to the female, she should be moved to another tank.
The babies hatch after a few days and are kept in the bubblenest for a few more days. Sometimes the babies fall out of the nest and hang on the side of the tank or on plants. When they start swimming about, you can feed them on green water, infusoria or boiled egg yolk. The link below tells you how to make these things.
The male will continue to look after the babies for the first few weeks after they swim around. Eventually he stops looking after them and builds a new bubblenest. When this happens, you should remove the babies so he doesn't kill the young males.
The rearing tank needs a coverglass to keep the air warm for the babies when they start to develop their labyrinth organ. If they start breathing in cold air, it can kill them.
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