Borneo Yellowfin Hillstream Loach (Gastromyzon viriosus)

The Borneo Yellowfin Hillstream Loach (Gastromyzon viriosus) is a little living river stone: a flattened, sucker-bodied oddball with a maze-patterned head and bold yellow and black banded fins. These are large, well-established specimens. Peaceful and endlessly watchable, hillstream loaches are an intermediate-level fish, not because they are delicate, but because they need a tank built around flow, oxygen, and grazing surfaces. Browse the rest of our freshwater livestock for tank mates.

Care Guide

• Tank setup: 20 gallons or more, long footprint preferred. Smooth river stones, rounded gravel, and open rock surfaces to graze and perch on recreate their shallow Borneo streams.
• Flow and oxygen are everything: aim for strong current and heavy surface agitation. A spare powerhead or an oversized filter outlet pointed along the rocks makes them thrive.
• Water: 68 to 77°F, pH 6.5 to 7.5. They appreciate the cooler end and pristine, well-oxygenated water. Avoid warm, still, low-oxygen tanks.
• Mature tanks only: their staple food is the biofilm and algae film that only develops in an established tank. Give the tank a few months of age, or seed rocks in a sunny window.
• Feeding: aufwuchs grazers. Supplement the biofilm with gel food, algae wafers, and occasional frozen daphnia or baby brine shrimp placed on the rocks.
• Group them: keep 3 or more. They squabble harmlessly over favorite stones, and the little turf displays are half the fun.

Specifications

Compatibility

Completely peaceful toward everything, including shrimp. Ideal tank mates are other current-loving fish like the Zebra Danio and small rasboras, plus bottom dwellers that stay out of their lane such as the Black Kuhli Loach or a group of Dwarf Chain Loaches. Avoid large aggressive fish and avoid warm-water slow tanks like betta setups, since the temperature and flow needs do not line up.

Recommended Foods & Supplies

• Repashy Soilent Green, the ideal gel food for aufwuchs grazers, it clings to their rocks
• Hikari Mini Algae Wafers sized for their small sucker mouths
• Hikari Algae Wafers for group feeding

FAQ

Is a hillstream loach an algae eater?
Partly. They rasp soft algae film and biofilm off smooth surfaces, but they will not mow down hair algae or clean a neglected tank. Think of them as grazers that need algae, not janitors.

Can I keep one in a betta or community tank?
Only if the tank runs cool with strong flow and high oxygen. A warm, still tank is the most common reason hillstream loaches fail.

Do they need a group?
They live fine alone, but a trio or more brings out natural behavior: stone-to-stone chases, fin flaring, and stacked perching. Their squabbles never cause damage.

Why is my hillstream loach on the glass?
Totally normal. Their fused fins work like a suction cup, and glass grows the same biofilm they graze on rocks. A tight lid still matters, they can climb above the waterline.