Fish
John Dory
Zeus faber · also called john dory, St Peter's fish
The John Dory is a fish built for a single trick — it is so flattened from the side that head-on it nearly disappears, letting it drift up to prey unseen before firing out a mouth that unfolds to almost the width of its whole body.
Overview
John Dory live near the seafloor in coastal and shelf waters of the eastern Atlantic, Mediterranean, and parts of the Indo-Pacific. Typically 30–40 cm, they have an oval, extremely thin olive-brown body with a dark yellow-ringed spot on each flank, hunting small fish, squid, and crustaceans.
Vanishing to hunt
Its knife-thin body presents almost no profile head-on, letting it approach prey closely before capturing it with a sudden, explosive forward thrust of the jaws.
A false eye and an old legend
The flank spots likely act as false eyespots to misdirect predators, and tradition holds they are the fingerprints of Saint Peter — hence the name St Peter’s fish.
Status
The John Dory is Least Concern, widespread and not globally threatened, though prized as a food fish and caught both directly and as bycatch.
John Dory: common questions
How does the John Dory hunt if it is such a slow swimmer?
It relies on stealth rather than speed, using its extremely thin, laterally compressed body as a form of camouflage during the approach. As it slowly closes in on a small fish or shrimp, it turns to face the prey head-on, at which point its knife-thin profile makes it very difficult for the prey to detect against the background, and it can drift to within striking distance almost unnoticed. Once close enough, it captures the prey not by chasing it but by suddenly shooting its jaws forward into a wide tube, engulfing the prey and a rush of surrounding water in a single rapid motion before the prey has time to react.
What is the dark spot on a John Dory's side for?
The prominent round black spot ringed with yellow on each flank is generally interpreted as a false eyespot, a marking found in many fish species that is thought to serve one or more defensive functions. It may make the fish appear larger or misrepresent which end is the head, causing a predator to strike at the less vulnerable rear of the body, or it may briefly startle an approaching predator, buying the John Dory a moment to escape. The same eyespot has also generated folklore, with one tradition holding that the marks are the thumb and finger prints of Saint Peter.
Why is the John Dory sometimes called St Peter's fish?
The name comes from a Christian tradition connected to a Gospel story in which Saint Peter, instructed to catch a fish, finds a coin in its mouth to pay a tax. According to the legend that grew around this, the dark, rounded spots on each side of the John Dory are the marks left by Saint Peter's finger and thumb when he held the fish to retrieve the coin. Because of this story, the John Dory is known as some variation of St Peter's fish in several European languages, though the same nickname is also applied to a completely different fish, tilapia, in other regions.
Is the John Dory good to eat, and is it fished sustainably?
It is highly regarded as a food fish, prized for its firm, white, delicately flavoured flesh, and commands high prices in markets and restaurants across its range, particularly in Europe and Australia. It is caught both as a targeted species and as bycatch in trawl fisheries aimed at other fish, and while it is currently assessed as Least Concern overall and is not considered globally threatened, the sustainability of specific John Dory catches varies by region and fishing method, so guidance from local seafood sustainability programmes is the best way to judge a particular source.