Forktailed Rainbow Fish
2019-07-15   Freshwater Fish


Less than two inches when fully grown, this small rainbow is a truly beautiful fish that fits in well with other small shoaling fish in a well-planted community aquarium. Providing that this fish is transferred over to its new aquarium home slowly, they will adapt to a wide range of water conditions ranging from soft and slightly acidic water to hard and alkaline.


Origins and Distribution

Forktailed Rainbow Fish are native to Peria Creek, Kwagira River, eastern Papua New Guinea, meaning that they are available in the wild in only a very small geographic area in the Milne Bay province. They occasionally travel into nearby rivers and tributaries, probably as a result of drainage among the different waterways. These fish prefer slow-moving streams lined with heavy vegetation; these environments make it easy for them to find their favorite foods: zooplankton, phytoplankton, and invertebrates.  Pseudomugil furcatus usually mate within the shoal and lay their eggs among feathery-leafed plants.

Today, very few Fork tailed Rainbow Fish are collected in the wild. Because they are easy to breed, they are bred in captivity for the aquarium trade.

Colors and Markings

The Forktailed Rainbow Fish or Pseudomugil furcatus is a very attractive species with blue eyes, a silvery body, and bright yellow stripes on the top and bottom of the body in the breeding season. Two upturned almost wing-like pectoral fins, bright yellow in color along with bright yellow dorsal fins in breeding season make this little gem a great attrition to any Community Aquarium.


Forktailed Rainbow Fish are a shoaling species and should be kept with between six and ten of their own kind. A generally peaceful fish, they can live comfortably with smaller goby or catfish species, danios, tetras, rasboras, dwarf cichlids, and other small rainbow fish. Do avoid keeping this species in a tank with slower-moving fish or fish with long, trailing fins as they do sometimes nip and can be a bit aggressive.

Forktailed Rainbow Fish Habitat and Care

When creating a habitat for your Forktailed Rainbow Fish, remember that their native environment is slow-moving water with a great deal of vegetation. To recreate a similar habitat, choose a 30 gallon or larger aquarium and add a dark, fine, sandy or rocky substrate. Decorate with river rocks, driftwoods, rooted plants, and floating feathery-leafed plants.  Floating plants and a dark substrate will not only bring out their colors to best effect, but the fish will be more comfortable and calm, with this touch of their natural environment added. Live plants are necessary for this fish to thrive. Be sure the water is well oxygenated; to do this, you'll need a good filtration system that doesn't create too much turbulence.

The Forktailed Rainbowfish is a very active fish, not only fast but agile as well, swimming, twisting and turning in and out of plants playfully all day. They are a middle zone fish and are in motion as long as aquarium lights are on. It is best to keep 2 males and 4-6 females for best and most active displays. Forktailed Rainbow Fish need plenty of time to acclimatize to a new tank environment. Quick exposure to a different water chemistry and temperature can shock their systems.

These fish are short-lived in nature, and because of this they mature quickly, breed young and are over the hill by one year of age. Males are prime at about 8 months, after 1 year to 15 months they will develop a pigeon chest, at which time they are too old or mature to breed. However many Forktailed Rainbow Fish live to be very old fish in a community aquarium, just no longer prime for breeding.

Forktailed Rainbow Fish Diet

A great advantage of this kind of fish is their feeding requirements: they have almost no special needs. Choose flake, micropellets, and small frozen foods such as daphnia, baby brine shrimp (Artemia nauplii), Cyclops, etc.

Sexual Differences

The males can be distinguished by their clearer colors and the striking fin shape (curved and almost wing-like) which are bright yellow. Females and juveniles have the same basic coloring as males, but the colors are not as brilliant.

Breeding the Forktailed Rainbow Fish

Over the last 10 years, this remarkable member of the Rainbow Fish family has faded almost completely from the Home Aquarium scene. It is unfortunate, because not only is this remarkable fish one of the easiest of the Rainbow Fish to keep in a community aquarium, it is also one of the easiest of its kind to breed.

The Pseudomugil furcatus is easy to breed, beautifully colored and relatively hardy. They are not fussy with regard to hardness or pH and seem to do well in a very wide range of water conditions.

Best Breeding Procedure 

Use 2 males and 6 females, each male will set up his own “territory” in the well-planted breeding tank. One of the males will take possession of a fine-leaved plant or breeding mop at a far end of the tank. You will notice that the females will stay in the middle of the aquarium during this mating ritual; the other male may take possession of another plant of breeding mop at the other end of the tank. 

You must get up at sunrise, or cause the lighting system in the breeding tank to simulate dawn, for it is then that the males will display for the females (worth getting up for, they become quite beautiful in their dances). Occasionally the males may have a brief skirmish for dominance, but they tend to ignore each other (this is why we suggest 6 females).

Eventually, a female will follow one of the males back to his chosen plant or breeding mop to spawn. You will know they are spawning when they dip to the lower reaches of the tank and swim up into the plant or mop close next to each other. As they reach close to the top of the plant, they push into each other and release eggs and milt together.

The most difficult part about breeding this remarkable fish is the wait for the eggs to hatch. It will take at least 14 days. There is a real chance of losing the eggs to fungus if left in the breeding tank. Best results are had removing the eggs to a sterile water tank, with fungus treatment.

Rearing the Fry

The fry (baby fish) are unusual among small egg layers in that they are free swimming and self-sufficient at time of hatching. They are large enough to accept live baby brine shrimp and powdered dry food.

Use a sponge filter in the fry rearing tank after 3 weeks, change 20% of the water each week, and feed small amounts of varying foods 6 times a day. With luck and good attention to detail, the fish will be sexable at 3 months and over an inch long.

                                                                                                                                                                                                                                                                                                                                                                              By Thomas Reich