Stiphodon semoni
Opal 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
Stiphodon semoni reaches around 50 mm total length and grazes algal biofilm from rock surfaces. It occurs in Indonesia, the Philippines, New Guinea, New Caledonia, Vanuatu and the Solomon Islands as well as Australia. A remarkable colour-change sequence has been documented in the field, with interacting males shifting between grey-pink, grey-green and blue-black within minutes; the formerly recognised Stiphodon alleni is now considered a junior synonym of this species.
Compiled for Home of the Rainbowfish from ANGFA sources: B. Hansen, “Stiphodons in Australia”, In-Stream 13, 2004, pp. 6–10; 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.