South American lungfish (Lepidosiren paradoxa) — 4-6cm

Overview

Tropical fish for sale UK enthusiasts seeking an extraordinary prehistoric species will find few fish as remarkable as Lepidosiren paradoxa, the South American lungfish. This ancient species originates from swamps, floodplains, and slow-moving waters of the Amazon, Paraguay, and lower Paraná River basins, where it has survived largely unchanged for millions of years. Available for sale UK in juvenile sizes from 4-7cm, the species grows into a massive fish reaching up to 125cm in length, demanding enormous aquarium space, expert-level care, and a lifetime commitment. The lungfish's ability to breathe atmospheric air using functional lungs represents one of the most fascinating adaptations in the fish world. Only experienced aquarists with appropriate facilities, resources, and long-term plans should consider this ultimate oddball species.

Appearance

Lepidosiren paradoxa displays an elongated, eel-like body with reduced, filamentous paired fins that resemble thin appendages. The body is robust and muscular, covered in large, overlapping scales and a thick mucus layer that protects the skin. Coloration ranges from olive-brown to grey with irregular dark mottling or marbling that provides camouflage in muddy, vegetated habitats. Juveniles appear more streamlined, while adults develop a thicker, more robust body. The head is broad and flattened with small eyes positioned dorsally, reflecting the species' reliance on chemoreception rather than vision for hunting. The mouth is large and equipped with tooth plates designed for crushing prey. The most distinctive feature is the functional lungs that allow the lungfish to surface and gulp atmospheric air—an obligate behavior essential for survival. Overall appearance is prehistoric and unique, unlike any conventional aquarium fish.

Natural Habitat

This species inhabits swamps, floodplains, oxbow lakes, and slow-moving, heavily vegetated waters throughout the Amazon, Paraguay, and lower Paraná River basins in South America. Natural habitats experience dramatic seasonal fluctuations, with wet seasons bringing extensive flooding and dry seasons reducing water levels significantly. During droughts, Lepidosiren paradoxa burrows into mud and enters a state of aestivation (dormancy), surviving months without water by breathing air through a mucus-lined breathing tube. Water conditions are typically warm, soft, acidic, and low in dissolved oxygen, making the lungfish's air-breathing ability essential. The species is nocturnal, hunting fish, crustaceans, mollusks, and other aquatic prey during nighttime hours.

Aquarium Setup

Housing a South American lungfish demands a truly massive aquarium or indoor pond of at least 2,000 litres—and realistically, substantially more for long-term success with adult specimens. The tank must be robust, with reinforced glass or acrylic capable of withstanding the fish's considerable size and weight. Use soft sand or bare-bottom substrate to prevent abrasion of the fish's sensitive skin and mucus layer. Provide hiding places using large, smooth rocks, PVC tubes, or driftwood arranged to create secure retreats. Avoid sharp decorations or rough surfaces. Lighting should remain subdued, reflecting the species' nocturnal habits. A secure, partially open lid is essential—the lungfish must have unrestricted access to the surface to breathe atmospheric air, and full coverage will suffocate the fish. Ensure excellent water quality with powerful filtration, though dissolved oxygen levels are less critical given the species' air-breathing ability.

Water Parameters

Maintain tropical temperatures between 24-30°C, with 26-28°C representing optimal conditions. The species tolerates cooler water but becomes less active and feeds less frequently. pH should remain between 6.0-7.5, with slightly acidic to neutral values (6.5-7.0) ideal. Water hardness can range from soft to moderately hard, though soft to moderate hardness better replicates natural Amazonian conditions. Ammonia and nitrite must be undetectable, while nitrates should stay below 40 ppm through efficient biological filtration and substantial weekly water changes. Given the enormous bioload produced by a large carnivorous fish, expect to replace 40-50% of the water weekly. Dissolved oxygen levels are less critical than for most fish, as the lungfish breathes atmospheric air, but water quality must remain high to prevent skin infections and disease.

Feeding

As a carnivore, Lepidosiren paradoxa requires a diet of meaty foods including earthworms, snails, insect larvae, crustaceans, whole or filleted fish, prawns, mussels, and appropriately sized frozen or thawed carnivore foods. Juveniles accept smaller live or frozen foods such as bloodworms, blackworms, and chopped shrimp. Feed juveniles every 1-2 days, transitioning to 2-3 times weekly as the fish matures. Avoid overfeeding, which rapidly degrades water quality and leads to obesity. High-quality pelleted foods formulated for large predatory fish can supplement the diet once the lungfish is acclimated. Feed during evening or nighttime hours to align with the species' nocturnal activity. Monitor body condition—a healthy lungfish appears robust but not bloated.

Behaviour

South American lungfish are primarily nocturnal, remaining hidden during daylight hours and emerging at dusk to hunt. The species moves with slow, sinuous movements, alternating between resting on the substrate and short bursts of activity. Swimming behavior appears eel-like, with the body undulating and the reduced fins providing minimal propulsion. The lungfish surfaces regularly to gulp atmospheric air, producing audible gasping sounds. This air-breathing behavior is essential and occurs every few minutes to hours depending on water temperature, activity level, and dissolved oxygen. The species is generally peaceful but will consume any tankmate small enough to swallow. Intelligence is evident in the fish's ability to recognize keepers and respond to feeding routines. Stress or poor water quality causes increased hiding, refusal to feed, or skin lesions.

Tank Mates

Selecting tankmates for Lepidosiren paradoxa is extremely challenging and generally inadvisable. Only very large, robust fish that cannot be swallowed and are not aggressive or fin-nipping have any chance of cohabitation. Most aquarists maintain this species alone to eliminate stress, reduce aggression, and simplify husbandry. Absolutely avoid small fish, shrimp, snails, and any creature that fits into the lungfish's mouth. Even large companions may be harassed or injured during feeding. In practice, a species-only setup is strongly recommended for this demanding giant.

Breeding

Breeding Lepidosiren paradoxa in home aquariums is extraordinarily rare and effectively impossible for private aquarists. In nature, the species breeds in seasonal wetlands where the male constructs and guards a nest, caring for developing eggs and young. Successful captive reproduction requires very large, specialized facilities, environmental cues from seasonal flooding, and mature adults in prime condition. Attempting to breed this species at home is impractical given the space requirements, long maturation period, and complexity of replicating natural spawning conditions.

Why Buy from Tropical Fish Co

Tropical Fish Co supplies healthy, carefully selected South American lungfish juveniles with comprehensive care guidance covering the extreme long-term commitment required. We ensure all specimens are feeding well on prepared foods before dispatch and provide detailed information on growth expectations, housing requirements, and the critical importance of surface access for air-breathing. Our experienced team candidly discusses the challenges of keeping this remarkable but demanding species, helping you make an informed decision. With nationwide UK delivery using specialist livestock couriers, your lungfish arrives safely in insulated packaging with oxygen. We support responsible fishkeeping and encourage only those with appropriate facilities and long-term plans to consider this extraordinary prehistoric fish. Choose Tropical Fish Co for rare, specialist livestock and expert guidance.