The Four-Eyed Fish Anableps anableps is truly an amazing creature that is celebrated for its curiously divided eyes. Although it doesn't actually have four eyes, the eyes are specially adapted for its surface-dwelling lifestyle. This unique fish is thought to have evolved specifically for the purpose of exploiting the narrow ecological niche between aquatic and terrestrial habitats.
Its two large, bulbous eyes are positioned on the upper side of the head. The eyes are split horizontally into two sections by a band of tissue. The upper lobe is flattened while the lower lobe is rounded, allowing it to see clearly both above and below water. While searching for foods at the surface and on the substrate below, it can literally keep an eye out for predators above, like herons or sea eagles, that would quickly snatch it from its watery home for a snack of their own!
These fish have an unusual and interesting lifestyle. They spend almost all of their time at the surface and rarely swim underwater. They will dive down when they spot a food item though, using their large paddle-like pectoral fins for a burst of speed. They will also leap onto mud and sand banks, exposed during periods of low-tide, to snatch terrestrial insects. These fish have been observed laying in the sun, sometimes for several minutes, before pushing their way back into the water.
These fish are members of the Anableps genus. There are three recognized species, though A. anableps is the one most commonly seen in the hobby. The species Anableps microlepis, commonly known as Foureyes, is sometimes available and looks very similar to A. anableps but lacks the white stripe on the top of its body. The Pacific Foureyed Fish Anableps dowei is rarely seen. Other common names A. anableps are known by include Anableps, Largescale Foureyes, Star Gazer, Four-eye, and Striped Foureyed Fish.
The A. anableps are an incredible species for an aquarist with some experience to keep. They are freshwater fish, but frequent river estuaries and mangroves swamps where the ebb and flow of the tide is constantly changing the salinity. They do best in a low-salinity, brackish aquarium. They are also schooling fish, happiest in a group of 6 or more and should never be kept singly or even as a pair.
Four-Eyed Fish are moderately hardy, but they are comparatively large livebearers, growing to around a foot in length.They need plenty of surface area, in fact due to their swimming habits, it is much more important for them than water depth. Juveniles need a good sized tank that's at least 4 feet long, while adults do need around 6 feet. A shallow water depth of 8" (20 cm) for juveniles and 12" (30 cm) for adults will suit them fine. They are easy to feed, accepting floating foods and even flake and frozen foods. Since they are excellent jumpers, the tank must be covered securely. They are moderately easy to breed as long as they are healthy adults and sexually compatible. They will usually mate and produce large fry that are easy to care for without any special setup.
These are peaceful fish and can be housed with other of similar temperament with the same water chemistry requirements. Just be cautious with vigorous surface-dwellers and voracious feeders. Good companions can be Sailfin Mollies, bottom-dwelling Gobies, Mudskippers, and even Orange Chromide Cichlids. Archer Fish and Monodactylus could make good tank mates as well, but they get large and will eventually need a tank with water that's at least 24" deep.
The Four-Eyed Fish Anableps anableps was described by Linnaeus in 1758.They are occur along a large range of the Atlantic Coast of Central and South America, and the island of Trinidad. They are not listed on the IUCN Red list of Threatened Species.
These fish belong to the Anablepidae family and are members of the Anableps genus, which currently has three recognized species. Like other members of their family, they are one-sided livebearers. On each specimen, the males gonopodium or female genital aperture, is located either on the right or left side. To mate they must pair with a member of the opposite sex that is sexually adorned on the compatible side. Spawnings are divided equally, with members adorned for each side.
The Anableps genus itself is generically referred to as the Four-Eyed Fish, though Anableps anableps is the one most commonly seen in the hobby. The species Anableps microlepis, commonly known as Foureyes, is sometimes available and looks very similar to A. anableps but lacks the white stripe on the top of its body. Pacific Foureyed fish Anableps dowei is rarely seen. Other common names A. anableps are known by include Anableps, Largescale Foureyes, Star Gazer, Four-eye, and Striped Foureyed Fish.
In the wild Four-Eyed Fish are found in freshwater lagoons as well as in the low-salinity waters of river estuaries and mangrove swamps. These waters have a constantly fluctuating salinity due to the ebb and flow of the tide. Shoaling groups of mature adult females swim along the water surface, with males following. During periods of low tide, these groups can number in the hundreds.
They feed mostly at the surface, though at times will swim to the bottom for food items as well as leaping to snatch terrestrial insect on the muddy and sandy banks. Their diet consists of insects and small crabs (Grapsidae family) and small fishes, as well as other invertebrates and diatoms including Gammarid amphipods, snails, mussels, and worms. They can remain on mud and sandy areas that are exposed to air during low tide and some have been observed leaping out of the water to rest in the sun for several minutes at a time.
Scientific Name: Anableps anableps
Social Grouping: Groups - They will swim on the surface in shoals, and often congregate in groups of several hundreds during low tide periods.
IUCN Red List: NE - Not Evaluated or not listed
The Four-Eyed Fish have a cylindrical, cigar-shaped body with large, strong paddle-like pectoral fins. The most striking feature of these fish are the double-lobed eyes. The eyes are large and project out from the upper side of the head. Each eye is split horizontally into two sections by a band of of epithelial tissue. Each half is designed to allow the fish to see clearly both above and below water. Some of the peculiarities are the upper lobe (used for vision in the air) is flattened and the upper cornea is thicker and enriched with glycogen. It is suggested this helps keep it from drying out and possibly helps protect it from UV light. The lower lobe (used for vision in the water) is rounded and the cornea is thinner.
The body is beige to gray, with the back being an olive-brown color with the sides and belly being a lighter cream. There is a white stripe running along the back, starting a a small v-shape just behind the eyes. There are several thin dark horizontal branching stripes along the sides that start just behind the large pectoral fins. One of its close relatives, the Foureyes Anableps microlepis, is sometimes available and is very similar in appearance, but it lacks the white stripe on the top of its body.
The females are larger than the males. In the wild the females can reach almost 12 inches (30 cm) in length while the males reach just shy of 8 inches (20 cm). In the aquarium females generally reach a length of only about 10 1/4 inches (26 cm). These fish become sexually maturity at about 8 months of age, when they've attained a length of 6 inches (15 cm). They have a lifespan of around 6 years, but can live up to about 8 years with optimal care.
As the male fish matures, the anal fin becomes modified into a narrow copulatory organ called a gonopodium. It is pipe shaped, greatly elongated and fused into a tube. It is a member of the Anablepidae family along with the White Eyes and Onesided Livebearers. The Anableps species are also one-sided livebearers. On these fish types, the males gonopodium and the females genital aperture are located either on the right or left side.
Size of fish - inches: 11.8 inches (30.00 cm) - Females are the largest at 12" (30 cm) in the wild, with the males at about 8" (20 cm). They are usually smaller in the aquarium with females at about 10 1/4" (26 cm) and males usually at about 6" (15 cm).
Lifespan: 6 years - On average these fish will 6 years, but can live up to 8 years if well cared for.
Fish Keeping Difficulty
The Four-Eyed Fish is an active swimmer, and though it will eat smaller fish, it is peaceful. When first imported it can be very delicate and prone to disease, notably bacterial skin infections which are difficult to cure. But once it's acclimated it is moderately hardy and easy to feed.
Though it is a durable fish once settled, it is suggested for an intermediate aquarist because of its needs. This good sized fish and must be kept in a group with no fewer than six of its own kind. it also needs a rather specialized aquarium setup. The aquarium must offer a lot of surface area with shallow water, and have brackish conditions. This fish is also an excellent jumper and will leap out of the tank if startled, so a tight fitting lid is critical.
Aquarium Hardiness: Moderately hardy
Aquarist Experience Level: Intermediate
Foods and Feeding
The Four-Eyed Fish are primarily carnivorous, though some suggest that they may consume a minute amount of vegetable matter. In the wild their diet consists mostly of insects and small crabs, in smaller amount they also consume small fish, other invertebrates, diatoms, amphipods, snails, mussels, and worms.
In the aquarium they will gladly eat floating food sticks, pellets, flake foods, and freeze–dried foods, and will especially enjoy live insects as large as crickets. Live or frozen foods such as brine shrimp, bloodworms, and tubifex worms, as well as daphnia can be offered to vary their diet. Some aquarists also make food mixes that incorporate freeze-dried plankton, fish, clams, beef heart, and shrimp.
These fish mostly look for food at the surface and surrounding land areas. It's a good idea to make sure to offer plenty of food at the water surface, as they will not readily chase food much below the surface of the water. There will be times they will dive for food morsels as well as leap onto a sandbank to get any food left there, but the majority of the food will be taken on the water surface.
Once settled in, this fish is not a picky eater. It should be fed a varied diet in small amounts several times a day. If they are not given plenty of protein-rich foods they will show poor growth, and some have reported that they can develop spinal deformities. Make sure that any uneaten food does not get a chance to foul the water. Housing them with mid-water feeders like Sailfin Mollies or Orange Chromide Cichlids, will help with food that sinks.
Diet Type: Carnivore
Flake Food: Yes
Tablet Pellet: Yes
Live foods (fishes, shrimps, worms): Some of Diet
Vegetable Food: Unknown
Meaty Food: Most of Diet
Feeding Frequency: Several feedings per day - This fish should be kept very well fed or else it will not grow properly.
Once the Four-Eyed Fish is acclimated, it is usually very hardy as long as the tank is well maintained. The brackish aquarium needs a good filtration system that can provide a large colony of nitrifying bacteria. Water changes should be kept regular to ensure that decomposing waste does not introduce too many toxins into the water. The tank should have regular partial water changes of 20% every 2 weeks to remove accumulating nitrates and maintain good water quality.
When doing water changes, remember to only replace the water that you have removed from the tank with salted water. Water which has evaporated left salts behind, so there is no need to add more salt if just topping off evaporated water.
Water Changes: Bi-weekly - Do partial water changes of 20% every 2 weeks to maintain good water quality.
The Four-Eyed Fish are comparatively large livebearers and very active fish. They need to be kept in a group of no fewer than 6 but would be even happier with a dozen or more. Since they spend virtually all of their time swimming at the surface, they need a tank that is broad rather than deep. A 65 gallon 4-foot long tank will work for a group of juveniles, but a group of adults will need something larger. A minimum 6-foot long tank of 125 gallons or more will be needed. These fish are excellent jumpers, so the aquarium will need a secure cover.
In their natural environment these fish live at or near the mouths of rivers. Enough salt should be added the the aquarium to simulate brackish water. For an adequate brackish tank, add 2 teaspoons of aquarium salt for every 4 gallons of water. The salinity conditions in the wild, however, are variable and it actually benefits and invigorates these fish to slightly vary the amount of salt in the tank on occasion. A specific gravity ranging between 1.005-1.015 is normally recommended. See additional information under Aquarium Glossary: brackish.
The brackish water tank needs quality water and these fish do produce a good amount of waste. A good filtration system that can provide a large colony of nitrifying bacteria is very helpful in maintaining stable water. Filtration systems such as a large external canister filter will remove much of the detritus, excess foods and waste. This in turn helps to keep the tank clean and maintain the general health of the fish.
The water needs to offer a lot of surface area and be shallow, with a depth of about 8" for juveniles and up to 12" for adults. The best setup for these fish is a bit unusual. Having a "shallow" and a "deep" end to providing an open area for swimming and an area with bog wood and smooth rocks for retreat, will help simulate their natural habitat.
Sloping the substrate so that shallow waters leads into smooth, slippery "sandbank" areas is optimal. This allows the fish to pull themselves up out of the water and grab food items without being damaged, or just to rest, and then push themselves back into the water. This area doesn't have to be created with sand, it can be smooth gravel anchored with smooth rocks and roots, or even just flat rocks. If keeping Mudskippers Periophthalmus spp. with your Four-Eyed Fish, rocks and roots in a shallow area will need to extend above the water surface. The Mudskippers will spend most of their time there, out of the water.
These fish like some plants, especially floating ones, but plants that tolerate brackish conditions are more rare, and these fish can do fine without them. Some of the hardier plants such as the Anubias spp. and Java Fern Microsorum pteropus may work. Provide bright lighting during the day will help to promote the growth of aufwuchs.
Minimum Tank Size: 65 gal (246 L) - A 65 gallon 4-foot long tank will work for a group of juveniles, but as adults they will need a 6-foot long tank of 125 gallons or more.
Suitable for Nano Tank: No
Substrate Type: Sand/Gravel Mix - Fine sand or a smooth, slippery small gravel will help keep these fish from damage.
Lighting Needs: Moderate - normal lighting - Bright lighting during the daylight hours will help to promote aufwuchs growth.
Temperature: 75.0 to 87.0° F (23.9 to 30.6° C)
Range ph: 7.0-8.5
Hardness Range: 8 - 25 dGH
Brackish: Yes - This fish must be kept in brackish conditions, A specific gravity ranging between 1.005-1.015 is recommended.
Water Movement: Moderate
Water Region: Top - These fish will spend most of their time swimming at the water surface.
The Four-Eyed Fish are peaceful but will eat fish that are small enough to fit into their mouths. They are a schooling fish and must be kept in a group of 6 or more. They should never be kept singly or even as a pair. They become extremely nervously and jittery without others of their own kind, and are actually happiest kept with a dozen or more.
As they thrive in a brackish water environment, they can be kept with other brackish fish of similar temperament. Sailfin Mollies, bottom-dwelling Gobies such as the Knight Goby Stigmatogobius sadanundio, Mudskippers, and even Orange Chromide Cichlids Etroplus maculatus make good companions. Mono Fish Monodactylus spp. can also make good tank mates, but they get large and will eventually need a deeper tank. Be cautious of vigorous surface-dwellers like the Archer Fish Toxotes spp., which also gets large, and voracious feeders such as the Spotted Scat Scatophagus argus.
Temperament: Peaceful - They are peaceful, but will eat tankmates large enough to fit in their mouths.
Same species - conspecifics: Yes - Keeping them in a school of 6 or more is essential for their well being.
Peaceful fish (): Safe - Keep them with other community fish that are not small enough to become a meal.
Semi-Aggressive (): Threat
Aggressive (): Threat
Large Semi-Aggressive (): Threat
Large Aggressive, Predatory (): Threat
Slow Swimmers & Eaters (): Safe
Shrimps, Crabs, Snails: May be aggressive - Small crabs make up a part of their diet in the wild.
Sex: Sexual differences
Females are considerably larger than the males when full grown. The male are more slender and develop a modification of the anal fin into a pipe shape, called a gonopodium, which is used in the reproductive process.
Breeding / Reproduction
The Four-Eyed Fish will breed if kept in a large tank with lots of surface area. The young reach sexual maturity by the time they reach 8 months of age and are 6 inches in length. However they are one-sided livebearers, where the males gonopodium and the females genital aperture are located either on the right or left side of the fish. Pairs must be compatibly matched in order to breed, i.e. a left-sided male must be bred with a right-sided female.
The male will approach the female from behind, repeatedly pushing against her to stimulate breeding. The gestation period is about two months and will generally produce 10 to 15 young. The fry usually emerge tail first and they are quite large, about 2 - 2.8 inches in length. The parents generally ignore the young but the fry may be eaten by other fish. It's important that the fry can swim freely and have adequate places in shallower sandbank areas to find shelter if needed, or moved to their own aquarium.
The baby fish will readily take small live foods such as Daphnia, fruit flies, or bloodworms, and also accept flakes and very small pellets. The fry will grow quickly if properly fed, and the females will grow fastest. For more information, see the guide for breeding Livebearing Fish: Breeding Freshwater Fish - Livebearers.
Ease of Breeding: Moderate - This fish requries a large tank with a lot of surface area to breed.
When first imported, Four-Eyed Fish can be very delicate and prone to disease, notably bacterial skin infections which are difficult to cure. But once acclimated they are generally quite hardy if well care for and provided a proper diet. They are subject to the same diseases as other tropical fish. The best way to proactively prevent disease is to give them the proper environment and give them a well balanced diet. They must be given plenty of protein-rich foods, otherwise they will show poor growth and it has also been reported that they can develop spinal deformities.
The closer to their natural habitat the less stress the fish will have, making them healthier and happy. A stressed fish is more likely to acquire disease. Anything you add to your tank can bring disease to your tank. Not only other fish but plants, substrate, and decorations can harbor bacteria. Take great care and make sure to properly clean or quarantine anything that you add to an established tank so not to upset the balance. For information about fish diseases and illnesses, see Aquarium Fish Diseases and Treatments.
The Four-Eyed Fish Anableps anableps are commonly available and moderately priced. The Foureyes Anableps microlepis are sometimes available and look very similar to A. anableps but lack the white stripe on the top of the body.