South American Lungfish

The South American Lungfish may not be pretty, but it is a pretty amazing fish nonetheless!

The South American Lungfish Lepidosiren paradoxa actually does have lungs and needs to breath air. These fish would make Darwin proud as they are said to be one of the oldest documented fish dating back millions of years and documented through fossils. This amazing fish has adapted to their environmental changes and continue to thrive. It is also known as the Amazonian Lungfish, Scaly Salamander-fish, and American Mud-fish.

The term “lungfish” is derived from their ability to extract oxygen from the atmosphere as well as water. The organs they use to do this are about as close to true lungs as any fish possesses. Their breathing apparatus is distinctly different from the types of auxiliary breathing apparatus found in anabantoids (the livebearing fishes) and other types of fish.

This Amazonian Lungfish uses its lung apparatus to survive in swampy areas that have the potential to completely dry up during the dry season. When most of the water has dried up and all that is left is mud, it will burrow down into ducts in the mud, and then close off the opening with mud balls. During this hibernation, its metabolism will decrease greatly, allowing it to survive for months underground. When the rains come again, it will come out of the mud to resume its life as a fish.

South American Lungfish can reach up to just over 4 feet (125 cm) in length. This a very unusual looking fish that can make an interesting showpiece. The young fish can be quite pretty with gold spots on a black background. As the fish grows, this color will fade to gray or brown.

The Amazon Lungfish is not very particular about water conditions and isn’t very active. A 60 gallon tank should be big enough for most home grown specimens. Scaly Salamander-fish will live a long time and eat a lot. They are usually kept alone, because they will eat just about anything they can get suck into their cavernous mouths. They like hiding places with lots of plants, but the surface must be unobstructed so they can get to the top of the tank to breathe.

For Information on keeping freshwater fish, see:
Freshwater Aquarium Guide: Aquarium Setup and Care

Habitat: Distribution / Background

The South American Lungfish Lepidosiren paradoxa was described by Fitzinger in 1837. These fish are found throughout most of the Amazon, predominately in the Rio Paraguay and Pio Parana basins. They can also be found in smaller numbers in Colombia, Venezuela, Peru, Brazil, French Guiana, Paraguay, and Argentina.

The L. paradoxa is the only member in Family Lepidosirenidae and the only lungfish species found in South America. Other common names it is know by are Amazonian Lungfish, Scaly Salamander-fish, American Mud-fish, and Amazon Lungfish. The species is not listed on the IUCN Red List.

Lungfish are an ancient group of very primitive fish. Lungfish make up the subclass Dipnoi and they are found in central South America, central Africa, and eastern central Australia. Some consider these fish to be the oldest form of evolution on the planet. Their pectoral and pelvic fins are very thin and can act like “legs” to help them somewhat walk on land and they can breath air. These fish have stayed the same physically for millions of years which have been proven from fossils. In ancient times they were found in saltwater. Now they are only found in freshwater, and this is the only known change to these fish.

The South American Lungfish is usually found in slow moving or stagnant waters. It occurs in creeks, swamps, rivers, and tributaries. Much of their environments are hypoxic, or low in oxygen, and some have no water at all during the rainy season. Their primary diet consists insects and insect larvae when young, but then feed on mollusks, fish, and insects as adults. There are reports that these fish will eat plant matter when their preferred food is not available. As dry season comes, the lungfish will dig and bury themselves and going into a near dead state and can stay that way up to 3-4 years.

• Scientific Name: Lepidosiren paradoxa
• Social Grouping: Solitary
• IUCN Red List: NE – Not Evaluated or not listed

Description

The body of the South American Lungfish looks rather eel like, being elongated and slender. Their pectoral fins are thin and thread-like, and their pelvic fins are a bit larger and set far back on the body. The newly hatched young look similar to tadpoles, but have branched external gills much like those of newts. After 7 weeks the young transform (called metamorphosis) into the adult form, loosing the external gills for gill openings.

Overall, adults have a dark gray or brown coloration. Juveniles will have gold spots on a black background. As the fish grows, this color will fade to gray or brown. The L. paradoxa can grow to over 4 feet (125 cm) in length and have a life span in captivity of 8 to 20 years.

• Size of fish – inches: 49.3 inches (125.10 cm)
• Lifespan: 20 years – These fish may live between 8 to 20 years in captivity.

Fish Keeping Difficulty

The South American Lungfish is actually very easy to care for if you can offer it the needed space as it grows. Remember that these fish are long lives and can reach 4 feet. Their water requirements are very low and they will learn to eat right out of your hand.

• Aquarium Hardiness: Moderately hardy
• Aquarist Experience Level: Intermediate

Foods and Feeding

In the wild, juvenile South American Lungfish will eat insects and insect larvae, but as adults they will feed on mollusks, fish and insects. They may be considered omnivorous, as it has been reported that they do ingest some unidentified algae and plant stems when their preferred food is not available. However they are primarily carnivores.and will eat all types of protein foods.

The easiest source of food for this lungfish are fish; live, dead, or in pieces. They will also eat insects, shrimp, crayfish, clams or most any living animal that is not quick enough to escape their vacuum like mouth. Tongs can be used to hold food in front of them to make sure it is eaten quickly and won’t have a chance to foul the water. Young Lungfish will need to eat twice a day but as they mature this will change to 2 or 3 times per week.

• Diet Type: Carnivore – Have been found to ingest some vegetative matter, but is functionally a carnivore.
• Flake Food: Yes – It may be possible to train this fish to accept processed food, but shouldn’t count on it.
• Tablet / Pellet: Yes
• Live foods (fishes, shrimps, worms): Most of Diet
• Vegetable Food: Unknown
• Meaty Food: All of Diet
• Feeding Frequency: Several feedings per day – The young will feed several times a day, but once matured 3 times a week is good.

Aquarium Care

Amazonian Lungfish are large messy fish. A large high quality filter is needed to keep the tank clear. The do not require a lot of work, a bi-weekly water change of 30% would be fine if using a quality filter.

• Water Changes: Bi-weekly – Water changes should be about 30% every other week.

Aquarium Setup

Other than when it is breathing, the South American Lungfish will spend most of its time on the bottom of the aquarium. Amazonian Lungfish are slow growers, but be prepared to eventually provide a home for a relatively large fish. Housing for this fish only needs to be large enough so that it can stretch out completely. They are not particularly active so a 60 gallon tank should be big enough for most home grown specimens. Make sure to have a strong filter to keep the tank clean. It is always good to use external filters and heaters as these giants can easily break these things.

Lots of swimming space is not necessary. They like more subdued lighting and some places to hide. Ideally they like a muddy bottom, some vegetation and maybe some roots or rock for security. Because this fish has very soft skin it could easily injure itself on jagged edges or rough gravel. This fish must also be able to reach the surface to breathe. Make sure the water’s surface is clear of obstructions as this fish is one of the few that can drown without air.

• Minimum Tank Size: 60 gal (227 L) – Requires little swimming space, but needs enough area to completely stretch out.
• Suitable for Nano Tank: No
• Substrate Type: Sand
• Lighting Needs: Low – subdued lighting
• Temperature: 75.0 to 82.0° F (23.9 to 27.8&deg C)
• Range ph: 6.0-8.0
• Hardness Range: 2 – 20 dGH – No exact values have been established, but due to their natural habitat being swampy they probably prefer water on the softer side. Your fish dealer can advise you further on what the indivdual specimen you purchase is accustomed to.
• Brackish: No
• Water Movement: Weak
• Water Region: Bottom – This fish will venture to the surface for air, but otherwise a bottom dweller.

Social Behaviors

This fish is a good candidate to be kept alone. They aren’t aggressive by nature, however it is highly predatory and will attack any fish that it thinks could be food. Although other large fish may survive in the tank with them, there is always the chance that the lungfish may attack or be attacked by other fish. In the case of the lungfish, this will not be caused by aggression but by hunger. On the other hand, slow movement and the soft skin of this lungfish make it an easy target for an aggressive tank mate.

• Venomous: No
• Temperament: Semi-aggressive – This fish is not aggressive by nature, however it is highly predatory and will attack any fish it deems edible. It is also slow moving and soft skinned, making it an excellent target for aggressive tankmates.
• Compatible with:
  • Same species – conspecifics: No
  • Peaceful fish (): Threat
  • Semi-Aggressive (): Threat
  • Aggressive (): Threat
  • Large Semi-Aggressive (): Threat
  • Large Aggressive, Predatory (): Threat
  • Threat
  • Shrimps, Crabs, Snails: Threat – is aggressive
  • Plants: Safe

Sex: Sexual differences

Unknown.

Breeding / Reproduction

The South American Lungfish has not been bred in captivity. In the wild, adults construct tunnel type holes in the mud that they line with vegetal matter. They then retreat into the tunnel and seal it off. During breeding season the adults do not breath through their lungs, so do not need to go to the surface for air. Rather they breath through use of their gills and through many thin-branched appendages which develop temporarily during this time.

The eggs are laid in the tunnel and guarded by the male, even after the eggs hatch into larvae. When newly hatched the young resemble tadpoles. During the larvae stage they breath through thread-like external gills, much like those of newts. After 7 weeks the young transform (called metamorphosis) into the adult form, loosing the external gills for gill openings.

• Ease of Breeding: Unknown

Fish Diseases

South American Lungfish are hardy fish when mature, but are subject to the same diseases as other tropical fish. One of the most common freshwater fish ailments is ich. Anything you add to your tank has the possibility of bringing 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.

With the Amazon Lungfish disease is not usually a problem in a well maintained aquarium. That being said there is no guarantee that you won’t have to deal with health problems or disease. The best way to proactively prevent disease is to give your Scaly Salamander-fish the proper environment and give them a well balanced diet. 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.

Lungfish are very resilient once established in a tank. Knowing the signs of illness, and catching and treating them early makes a huge difference. It is recommended to read up on the common tank diseases. For information about freshwater fish diseases and illnesses, see Aquarium Fish Diseases and Treatments.

Availability

The South American Lungfish are commonly available but this is not a fish that many stores will carry on a regular basis. It is definitely a candidate for a special order.

References

• Animal-World References: Freshwater Fish and Plants
• Dr. Rüdiger Riehl and Hans A. Baensch, Aquarium Atlas Vol. 2, Publisher Hans A. Baensch, 1993
• Lepidosiren paradoxa (Fitzinger, 1837) South American lungfish, Fishbase.org

 South American lungfish (Lepidosiren paradoxa) (Image Credit: JSutton93, Wikimedia Commons CC BY-SA 4.0 International)