Threadfin Butterflyfish Identification Guide
How to recognize a threadfin butterflyfish by the trailing filament off its dorsal fin and diagonal-line pattern.
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Key identification features
- Pale yellow to white body covered in fine, diagonal crosshatched lines running in two opposing directions
- Bold black vertical bar running through the eye, breaking up the outline of the eye from predators
- Long trailing filament extending from the rear of the soft dorsal fin, most visible on adults and lost or shortened on some older individuals
- Black spot near the base of the rear dorsal fin in some populations, though it can be faint or absent in others depending on region
- Yellow rear body and tail; grows to about 23 cm
Common look-alikes
- Vagabond butterflyfish has a similar diagonal-line pattern but lacks the trailing dorsal filament and shows bold black bands on the tail instead
- Raccoon butterflyfish shares the black eye bar but lacks the elongated dorsal fin thread that gives this species its name
Where you'll see one
Found on coral reefs, in lagoons, and around rubble areas across the Indo-Pacific and Red Sea, usually in pairs or small groups at shallow to moderate depths.
Frequently asked questions
What's the single best field mark for a threadfin butterflyfish?
The thin trailing filament extending off the back of the dorsal fin, visible on most adults, gives this species its name and best separates it from similarly patterned butterflyfish.
How do I tell it apart from a vagabond butterflyfish?
Vagabond butterflyfish lacks the dorsal fin thread and has bold black bands on the tail, while threadfin butterflyfish has a plainer yellow tail.