Sicyopterus lagocephalus
Blue Stream Goby (also Rabbithead Cling Goby)
Sicydiine gobies, or “cling gobies,” are a subfamily (Sicydiinae) of around 80–90 species in eight genera, more than half described only in the last twenty years. Every species is amphidromous: adults live and spawn in fast, clear freshwater streams, but the tiny hatchlings are swept out to sea, where they spend a planktonic larval phase before returning to fresh water as post-larvae — often in a synchronised pulse the day after a full moon — and migrating back upstream, sometimes climbing waterfalls along the way using a sucking disc formed from fused pelvic fins. Most species graze algae and biofilm from rock surfaces using a distinctive fleshy sac of replacement teeth above the upper jaw, and males in breeding condition are typically brilliantly coloured, in sharp contrast to drabber females. All Australian cling gobies are protected species — look, but don’t touch.
Species Summary
Sicyopterus lagocephalus may have the broadest natural distribution of any freshwater fish in the world, recorded from the Comoro and Mascarene Islands in the western Indian Ocean right across to the Society Islands in the eastern Pacific, and from Japan south through Australia, New Guinea and New Caledonia. In Australia it ranges from the Bloomfield River north of Cooktown south to Nyleta Creek, its southern limit. Breeding males are bluish to greenish with an orange-red tail carrying a distinctive dark “horseshoe” marking on the caudal fin; females are drab brown. It reaches up to 130 mm total length, is strictly herbivorous, grazing algae from rock surfaces, and its gonad cycle runs roughly November–August, with spawning tied to the rainy season.
In the field, Sicyopterus lagocephalus has been seen grazing in loose groups in fast riffles, with one dominant male chasing off smaller females — territorial behaviour around a shared algal grazing ground rather than the courtship-focused territoriality of many other gobies.
Compiled for Home of the Rainbowfish from ANGFA sources: A. R. Tappin, “Sicyopterus lagocephalus (Pallas, 1774) Blue Stream Goby”, In-Stream 22, 2013, pp. 20–24; A. R. Tappin, “Australian Sicydiine Gobies”, In-Stream 23, 2014, pp. 12–18; J. Lenagan, “Cairns to Weipa and back, through a new lens: Part 2. Gobioides of the Wet Tropics”, Fishes of Sahul 34, 2020, pp. 1642–1657.