Freshwater moray eel

Gymnothorax polyuranodon

Also known as Freshwater tiger moray, Many-toothed moray

FreshwaterBrackishFish

Freshwater moray eel (Gymnothorax polyuranodon) — The Wet Spot Tropical Fish · Used with permission

Care at a glance

Temperature: 73–82°F (23–28°C)
pH: 7.0–8.2
Adult size: 35.4 in (90 cm)
Minimum tank: 159 gal (600 L)
Temperament: Aggressive
Social behavior: Solitary
Tankmates: Tankmates with caution
Swim level: Bottom
Difficulty: Difficult
Breeding: No record
Rarity: Rare
Origin: Rivers of the Indo-Pacific islands, from Sri Lanka to Fiji
Family: Muraenidae

Overview

This is a true moray that lives in fresh and brackish rivers, a large, aggressive predator for a dedicated system only, kept strictly on its own. It hides in caves and among rock by day and hunts at night, and it will eat any tankmate small enough to swallow, so tankmates are a genuine risk and are best avoided altogether. It is a determined escape artist, so a heavy, sealed lid is not optional. Feed meaty foods on a stick to keep fingers clear: strips of fish, prawn, and other seafood. It grows close to a metre and needs a large tank of at least 600 litres with secure rockwork and a tight cover.

In the wild

Unlike most so-called freshwater morays, this species genuinely lives in rivers, ranging across the islands of the Indo-Pacific from Sri Lanka to Fiji, usually within a short distance of the coast. Keep it in hard, alkaline water with a pH of 7.0 to 8.2 and a temperature of 23 to 28 degrees Celsius, and many keepers add some marine salt. Provide caves, rock, and dim light over a sand or fine gravel bed.

Good to know

It belongs to the moray family, Muraenidae, and is one of the larger freshwater fishes of its region, most individuals staying under a metre, though exceptional wild fish are recorded to about 150 centimeters. It is boldly marked with dark leopard spotting. It is catadromous, migrating to the sea to spawn, where its young drift as transparent leptocephalus larvae before entering rivers, so it is effectively not bred in home aquaria.

Did you know

Most freshwater morays in shops are really estuary fish that only tolerate fresh water for a while. This leopard-spotted species is the honest article, able to spend years in genuinely fresh river water far from the sea.