Nan River loach

Hemimyzon nanensis

Also known as Nan hillstream loach, Royal butterfly loach

FreshwaterFish

Care at a glance

Temperature: 64–75°F (18–24°C)
pH: 6.5–7.5
Adult size: 2.8 in (7 cm)
Minimum tank: 24 gal (90 L)
Temperament: Peaceful
Social behavior: Social
Swim level: Bottom
Difficulty: Difficult
Breeding: No record
Rarity: Rare
Origin: Nan River basin, northern Thailand
Family: Balitoridae

Overview

This is a fish for a dedicated river tank, not an ordinary aquarium, and it is one of the harder loaches to satisfy. Keep a small group on the bottom of a tank with torrent-grade flow, cool or even unheated water, and constant high oxygen. In the right current they graze the film on stone and take tiny sinking foods; in a warm, still tank they slowly starve of oxygen and current. They are peaceful and belong only with other cool, fast-water specialists. Feed micro sinking pellets and small frozen foods worked down among the rocks. Plan on about 90 liters with heavy pumps.

In the wild

The Nan River loach comes from cool, fast riffles in the upper Nan basin of northern Thailand, a headwater of the Chao Phraya, over rock, gravel, and sand filmed with algae. Keep it cold-leaning, 18 to 24 degrees Celsius, with strong current, very high oxygen, and pH around 6.5 to 7.5. Shallow, brisk, well-lit water over smooth stone comes closest to its native stretch.

Good to know

Hemimyzon nanensis was described by Doi and Kottelat in 1998 and reaches about 7 centimeters. Hemimyzon are among the most current-adapted of the river loaches in the family Balitoridae, their bodies flattened almost to a pancake and their paired fins broadened into fans that grip wet stone. It has not been bred in aquariums.

Did you know

Until this fish was found, its genus was known only from China and Taiwan. Describing it from northern Thailand in 1998 stretched the known range of Hemimyzon well down into Southeast Asia.