The John dory is very distinctive – you can’t mistake it. Its deep head and body and compressed sides give it an almost two-dimensional appearance, flattened from side to side and as thin as a dinner plate from the front. A feature of its head is the enormous mouth and protrusible upper jaw which slides down when the mouth is opened to give an absolutely immense gape. The spiny rays in the dorsal fin and the rays in the pelvic fins are enormously long, and there are four very strong spines in the front of the anal fin. A double row of sharp spiny scales run round the edge of the body. In colour the John dory is grey or yellowish with mottled markings and a pale belly. There is a dark blotch ringed with yellow in the centre of each side.
The ambush approach
Although the dory can swim strongly when startled and struggle if hooked by an angler, its normal lifestyle is one of leisurely drifting, propelling itself forwards by gentle undulations of the tail and the dorsal and anal fins. In the open sea it has the habit of hovering beneath driftwood or a slow-moving rowing boat, apparently content to shelter in the shadow cast by the solid object. In shallow water it hangs around close to rocks or beside seaweeds, pier pilings or wrecks. It rarely moves quickly, merely adjusting its position by gentle movements of the fins.
That the dory is a highly successful predator of fish – many of them active species – is perhaps surprising. It owes its success to its ambush style of feeding. When a potential food fish approaches, the dory turns head-on to look straight at it. The dory’s eyes are very mobile and it can look forward with an unobstructed view to the tip of its snout (or backwards to see if anything threatens from behind).
The dory then moves very slowly forwards and when the prey is a few inches from its snout, swings open its lower jaw, shooting its upper jaw forwards and spreading its cheeks and gill covers outwards. Water rushes inwards and the dory makes a lightning-fast pounce, securing in its jaws all but the fastest-moving, most alert of fish and squid.
Its diet includes a wide range of fish, including sandeels, pouting, young pollack, wrasses, even herrings, pilchards and anchovies, as well as the common small squids on our coasts.
Adults are generally solitary fish; divers often encounter single individuals hovering in a stealthy manner among strands of seaweed which provide good cover – and camouflage. Anglers catch them by accident – they don’t fish specially for them, although the dory makes good eating if you don’t mind its strange appearance.
Breeding ocurs in summer in water of less than 100m (330ft). The eggs float near the surface. By the time the young fish is 7mm (Van) long it looks like a dory, with a deep body, massive head and huge mouth. The youngsters, living near the surface, are truly formidable predators on the myriad tiny crustaceans and small fishes of the ocean surface.
The dory breeds successfully only off the southern coasts of Britain, and most of those caught to the north are wanderers, carried by ocean currents.