Rhinogobius sp. 'CB'

Overview

Rhinogobius sp. 'CB' is a widespread but formally unresolved Japanese goby, its code referring to dark cross bands. Populations include both migratory and entirely freshwater life histories. The code alone cannot determine larval salinity requirements.

Distribution & habitat

It occurs across much of Japan except Hokkaido and is among the commonest Japanese forms in its unresolved species complex.

Small tributaries and streams provide gravel, rocks, boulders, and exposed bedrock. Flow, depth, and turbidity change with the seasons.

Breeding

Some populations are amphidromous. Adults live and spawn in fresh or brackish streams, while newly hatched drifting larvae move downstream to the sea. Early development continues in estuarine nursery areas ranging from brackish to marine conditions. At a later stage fish move upstream, either entering freshwater tributaries or remaining in tidal lower reaches.

Landlocked populations complete the entire cycle in fresh water and generally produce larger eggs. Salt addition is therefore not universally required, while freshwater-only rearing cannot be assumed for every origin.

Wild reproductive activity occurs from summer into early autumn. Males defend temporary spawning areas around relatively flat stones, with eggs deposited underneath. After spawning, the female is driven away and the male tends and guards the brood.

Notes

CB abbreviates cross band, a pattern code rather than a formal species epithet. Membership of the Rhinogobius brunneus complex does not establish identical biology among every local population.

A naked or sparsely scaled predorsal area is a comparative character, not evidence of a wholly scaleless body. Practical care and breeding choices require dependable population information.