A rare amphidromous species, found in lowland streams and hillstreams with good ocean to stream linkage. Thus, it is fairly restricted in Hong Kong, due to the channelizations of most natural watercourses.
Like most gobies, S.atropurpureus is largely benthic- staying at the bottom of various streams and pools. They're algae grazers and tend to like areas with high flow, strong sunlights, and of course high algal coverage on boulders.
Identification: It is a medium-sized goby with elongated and cylindrical body. Its head is relatively small and flattened. All fins are oblique and there are small dots scattered on the dorsal and caudal fins. The fish exhibits obvious sexual dimorphism, in which females are yellowish brown with two longitudinal black stripes whereas males are metallic green without any stripes on body (AFCD). This species ranges from 3-5 cm in total length.
Left (male), Right (female)
Habitat: Juveniles can be found nearshore and estuaries, whilst adults tend to be in lowland streams and hillstreams with good ocean to stream linkage.
AFCD: Records from a few streams in North-East of New Territories and on Lantau Island.
Personal experience: A rare species due to their restriction to habitats with good water quality and stream to ocean connectivity. Additionally, they are also specialized algal feeders and prefer stream sections of fast flow with high algal coverage on rocks.
Fellowes et al. (2002): Global Concern
AFCD: Species of Conservation Concern Personal note: They're commonly sold in aquariums at Tung Choi Street. However, in addition to their rarity they also have complex breeding habitats due to their amphidromous nature, thus reproduction cannot be mimicked. Therefore, aquaria does not help conserve this species.