Japanese Fluvial Sculpin — a Cottidae from Japan, peaceful except over a chosen cave. Reaches 4–8 cm; pairs or small groups with ample hiding spots. 20–26 °C.
Care parameters
Water temperature
20–26 °C
pH
6.5–7.5
GH hardness
5–15 dGH
Adult length
4–8 cm
Minimum tank
77 L
Water layer
Middle of the water column
Difficulty
Moderate
Temperament
Peaceful except over a chosen cave
Origin
Japan
Species overview
Cottidae species Cottus pollux comes from Japan. A benthic percher that spends its days darting between rock, glass and cave — structure decides its temperament. It swims in mid-water. Adults reach 4–8 cm. Pairs or small groups with ample hiding spots. Caves, stable pairs and clean sand keep this fish far calmer than open, bare tanks ever will. Maintain 20–26 °C at pH 6.5–7.5. Undemanding once its core needs are met.
Native biotope
Habitat
Warm freshwater streams and lakes
Flow
Still to gentle current
Dissolved O₂
Moderate oxygen levels
Aquascape & hardware
Substrate
Fine sand and gravel
Hardscape
Driftwood and smooth stones
Plants
Hardy common aquarium plants
Temperament, diet & tankmates
Schooling
Pairs or small groups with ample hiding spots
Diet
Predatory bottom-picker; offer varied small fare
Recommended tankmates
Non-goby bottom fish — Ignore its territorial posturing
Avoid keeping with
Large aggressive fish — Shatter its sense of cover
Breeding & notes
Sexual dimorphism
Subtle external differences
Breeding method
Lays eggs in a sheltered cavity; males fan and guard