Threadfin sicyopterus

Sicyopterus longifilis

Also known as Funky goby, Longifilis goby

FreshwaterFish

Care at a glance

Temperature: 73–81°F (23–27°C)
pH: 6.5–7.8
Adult size: 3.9 in (10 cm)
Minimum tank: 29 gal (110 L)
Temperament: Peaceful
Social behavior: Social
Swim level: Bottom
Difficulty: Difficult
Breeding: No record
Rarity: Rare
Origin: Indonesian and New Guinea streams
Family: Oxudercidae

Overview

This is a river-current grazer, and the hardware comes before the fish: it needs a mature tank with strong flow, high oxygen, and a good film of algae and biofilm growing on sunlit rock. It works the bottom, using a sucker-like mouth to rasp that film off stone, so a bare or spotless tank will slowly starve it. It is peaceful and can be kept in a small group of its own kind alongside other calm, flow-tolerant fish. Supplement the grazing with algae wafers, blanched vegetables, and some frozen foods. Because it is active and needs open swimming lanes, give it a tank of around 110 liters or more.

In the wild

Sicyopterus longifilis holds station in fast, clear hill streams across eastern Indonesia and New Guinea, clinging to rock in the current where sunlight grows a carpet of diatoms and algae. Recreate that with 23 to 27 degrees Celsius, a pH of 6.5 to 7.8, strong flow, and smooth stones and cobbles left to grow a natural film. Bright light over open rock helps that grazing surface build. Plants are optional; oxygen and current are not.

Good to know

A goby of the family Oxudercidae, subfamily Sicydiinae, it grows to about 10 centimeters. Its species name refers to a long filament: mature males draw the second dorsal fin out into a trailing thread. Like other Sicyopterus it is amphidromous, with a marine larval stage, and the returning young gather in such numbers that in parts of its range they are netted and eaten. No aquarium breeding has been documented.

Did you know

The trailing thread that names this goby is display gear. In a strong current a courting male streams that extended fin ray out behind him like a pennant over the patch of rock he grazes and guards.