Chaetodon guentheri
Uncommon but reliable on reefs in New South Wales and Queensland, this small butterflyfish suits water from 20 to 29°C year-round.
A small, disc-shaped butterflyfish around 12 cm, with a white to pale grey body and a bold black-edged patch across the rear dorsal fin. A dark vertical bar runs through the eye, and fine chevron-like scale markings show on the flanks when you get close. There's no dramatic colour split between juveniles and adults, so size and the dorsal patch are the quickest cues underwater.
Usually spotted picking at the reef alone or in loose pairs rather than in the tight schools some butterflyfish form, working crevices and rocky outcrops for small invertebrates. It tends to hold its ground rather than bolt when divers approach, making for a decent look if you slow down. Most sightings come from open reef and rocky reef edges rather than deep drop-offs, well within recreational depths.
It ranges further into cool temperate water than most butterflyfish, which is why it turns up on rocky reefs around Sydney as readily as on tropical reef in Bali.
No clear seasonal pattern shows in the sightings, and its wide temperature range of roughly 20 to 29°C means it's present year-round wherever it's found, from cooler NSW reefs to warmer Bali waters.
Reef neighbours a diver could mistake it for. Use the identification notes above to tell them apart.
Most reliably logged along New South Wales, particularly around Sydney's temperate reefs, with a strong secondary presence in Queensland. It also turns up on reefs in Bali, Indonesia, making it one of the few butterflyfish comfortable on both temperate and tropical Australian reefs.
Mapping where Günther's Butterflyfish is logged…
New South Wales, especially around Sydney, is the strongest area for sightings, with Queensland also producing regular records. It's also found on reefs in Bali, Indonesia.
There's no strong seasonal signal in the sightings, and its broad temperature tolerance means it's seen on reefs throughout the year rather than in one particular season.
Look for a small, pale grey to white butterflyfish around 12 cm with a black-edged patch on the rear dorsal fin and a dark bar through the eye. It lacks the bold yellow or orange banding of many tropical butterflyfish.
They reach around 12 cm, making them one of the smaller butterflyfish divers encounter on Australian and Indonesian reefs.
No. They're small reef carnivores that pose no threat to divers and are generally approachable rather than skittish.
Site and sighting data is aggregated from diver logs, iNaturalist and GBIF. For taxonomy and conservation status:
Melon Butterflyfish
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