Caring for and Breeding the Moonlight Gourami

Trichogaster microlepis are a sight to see once in a display aquarium

A number of fish are not as popular as they should be. For my money, leading this list would have to be the moonlight gourami (Trichogaster microlepis). This fish is peaceful, undemanding when it comes to water conditions, and beautiful in a plain and understated way. When they have moonlight gouramis, most local fish stores usually have juveniles; these fish do not gain their full beauty until they are young adults. Small moonlight gouramis are what my business partner in my first fish store used to call “little gray fish.” I hope that in this article, I will convince you to look past the gray and to keep some of these fish in the future.

The moonlight gourami is found wild in the Mekong River Valley in Asia; (an online fish information database) also reports that there is a population of these fish introduced into Colombia, escapees from a breeding effort. All of the fish in the hobby today come to us from commercial fish farming operations either in the Far East or Florida.
Moonlight gouramis can grow to 6 inches in length for males and smaller for females. This fish is a beautiful silver color, with highlights of subtle greens and golds on the sides of adult specimens. In addition to being larger, male moonlights have a longer, more pointed dorsal fin, and their ventral fins are orange-red, while the females have yellow ventrals.

Like all gouramis, their ventral fins are thin, round “feelers.” These are more than just fins — they are sense organs.
It is interesting to watch gouramis as they cruise around an aquarium, poking in front and to the side with their ventral fins much like a blind person with a cane. They use their feelers to find food, which they search for constantly. These specialized fins also come into play when the fish are courting and spawning. Another distinguishing trait of moonlight gouramis is that the upper half of their eyes are red.

Moonlight gouramis are in the suborder of Anabantoidae, or anabantid fish, also known as labyrinthfish. Gouramis and bettas  make up most of the fish that are labyrinths, and they are so named for the labyrinth organ in the head above the mouth. The labyrinth is a folded organ that has excellent blood flow, and it gives these fish the ability to take oxygen directly from the air. When you see a gourami or betta coming up to the top of the water and taking a gulp of air, this does not mean it is in distress, as it would with other fish — it is perfectly natural for them to do this. In fact, some fishkeepers have stated that anabantids can actually “drown” if they are not able to take in gulps of air.

Tanks and Tankmates
Moonlight gouramis are hardy and easy to keep. They make ideal fish for first-time hobbyists, except for the fact that they get a little large; also, they are not always available in local fish stores, and if available, they are usually juvenile fish with little of the subtle colors and appeal of the adults. These fish are perfect community tank inhabitants, as they are peaceful and tolerant of less-than-ideal water conditions. The only time there will be any mild aggression is between males if they are sparring for the attention of a female.
They prefer soft and acidic water conditions, but because they are bred in water with a neutral pH and moderate hardness (especially in Florida), they will also adjust to these water parameters. They do best in trios of one male and two females, if possible. Definitely avoid having a single moonlight gourami in a community aquarium, as they have been known to “go rogue” without any conspecifics in their tank. They prefer temperatures in the high 70s to low 80s (degrees Fahrenheit), with very little water movement. These fish come from slow-moving streams and lagoons in dense tropical conditions of high heat but little direct sunlight.
Long tanks are best for moonlight gouramis, as they are long fish themselves, and they swim most of the time in the mid levels of the water column.

They also do best in a heavily planted tank, but there are certain considerations. Not all of the plants that we keep in the hobby will do well at the higher temperatures that moonlight gouramis prefer; check with your local fish store about plants they recommend for warmer tank conditions. My experience has been that water sprite (Ceratopteris thalictroides), hygro  (Hygrophila spp.) and cabomba  (Cabomba spp.) will do well at these higher temperatures, as will most of the Amazon swordplants  (Echinodorus spp.). Floating plants should always be included in a tank for these fish, as they like to hang out under them, and they will also use them for building their bubblenests.

Feeding moonlight gouramis is no problem, especially since all the fish in local fish stores have been commercially raised and are used to eating dry foods. Any good dry prepared food will be fine, though it is best if you use a food that will float, at least for a little while.
Looking at the fish, you will notice that in addition to a concave forehead, the moonlight gourami has an upturned mouth, which tells us that they are used to taking their food mostly from the surface. They will, however, also pick around any and all places in the aquarium looking for food, including along the substrate.
They will nibble on soft-leaved plants but not to the point of totally destroying a plant, and it is a good idea to include some plant material in their diet. Blanched zucchini or romaine lettuce can be offered, or you can include dry prepared foods with Spirulina algae in them. Moonlight gouramis are rather timid feeders, so it is important that they not be housed with other fish that are more aggressive feeders. Moonlights need to be able to eat slowly and not have to compete with eager eaters, such as danios or rainbowfishes.
In addition to dry prepared foods, freeze-dried plankton is an excellent “treat” for moonlight gouramis. The small (quarter inch or so) creatures float for a long time on the water surface, and the fish love to hunt for them among the floating plants.

Breeding Moonlight Gouramis
Moonlight gouramis will breed easily for any hobbyist, as long as a few conditions are met. These fish are bubblenest builders (the best-known bubblenest builder is the Siamese fighting fish, Betta splendens), which means that the male constructs a nest at the surface of the water with bubbles that he produces. These bubbles have a lot of mucus, and any male moonlight gourami worth his salt can easily build a nest 4 or 5 inches across and almost half an inch tall. To give him a start on the nest, provide some floating plants in the breeding tank; some breeders use half of an upturned Styrofoam cup. The idea is to give the male an anchor for his nest.
All that is needed to breed a pair of moonlight gouramis is a 15-gallon tank. The water should be clean, soft and acidic, and initially kept at around 74 degrees. Other than the heater, all you need in the breeding tank is a small sponge filter bubbling very slowly — say one bubble every couple of seconds.

Condition the male and female (preferably in separate tanks) on a meaty diet of live or frozen bloodworms, blackworms, Daphnia or Cyclops. Keep the male in the tank by himself for a couple of days, continuing to feed him heavily, and making sure that all the food is being eaten. Each day, raise the temperature by a degree or so until you are at 78 degrees. Float the female in a plastic breeding trap in the tank so that the male can see her, and do a 30-percent water change with warmer water (say at 84 degrees). The combination of seeing the female and the warmer freshwater should be all the triggers that the couple needs.

If the male has not already been building his bubblenest, he will begin doing so shortly. When he appears to be done and satisfied with his work, he should spend more time courting the female. When the courting behavior begins, release the female into the main tank with the male. The male should immediately begin to court the female in a major-league way. Soon he will maneuver her under his nest, and the pair will curl around each other. The female will release eggs at each embrace, and the male will fertilize them as they are released. The male then picks up the eggs in his mouth and blows them into his bubblenest. After repeating the spawning embrace many times, the female will run out of eggs. At this point, she will want to move away from under the nest. It is important that you have a dense thicket of plants (a sinking spawning mop will also work fine) for the female to retreat into, as the male will become protective of his nest and may rough up the female if she doesn’t have a place to hide.

The male will then guard his nest, and take care of the babies until they hatch and become free-swimming. It usually takes five to seven days for the babies to become free-swimming, as soon as they do, remove the male. Lower the water level to 4 to 5 inches, as you do not want there to be too much water pressure from the deeper water on the delicate labyrinth organs of the babies as they develop. Feeding the babies and keeping their water clean are the next big challenges.
For the first week after they are free-swimming, the baby moonlight gouramis will only be able to eat microscopic food in the form of green water or APR (artificial plankton and rotifers) or other commercially available foods for very small baby fish. The babies must be fed two or three times a day, and in between each feeding, drain 10 percent of the water from the tank with a piece of air line tubing. This not only provides for necessary daily water changes, but it is important to remove uneaten food from the bottom of the tank on a daily basis.
Keep a tank of water at the same temperature, pH and hardness as the breeding tank, and use this to replace the water each time you do the 10-percent water change. One other important thing is to keep the top of the tank tightly covered. This is because as the labyrinth organ develops, it is critical that the air temperature be as close to the water temperature as possible.
Moonlight gouramis are terrific aquarium fish. They are peaceful and hardy, will eat anything and are tolerant of a wide range of water conditions. They also happen to be gorgeous fish in their understated way. If your local fish store does not have them in stock, ask them to bring some in. Once you take yours home, you will surely enjoy them. AFI

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Fish · Freshwater Fish