Atlantic bluefin tuna

The biggest bony fish most divers will ever meet in the Mediterranean, and the fastest. The body is a perfect metal-bright spindle: deep blue-black across the back, polished silver on the flanks with faint pale spots and bars in live fish, and a white belly. The pectoral fins are short, the tail is a stiff crescent, and a row of small yellow finlets runs along the top and bottom of the tail stock. Everything about it is built to shed drag, right down to fins that fold into slots.

Mediterranean fish you might see are commonly 150 to 250 cm and a few hundred kilos, with the species reaching three metres and well over 400 kg. They travel in small groups or singly, cruising fast through open blue, and an encounter is usually over in seconds: a shape hardens out of the haze, passes, and is gone.

Around the Maltese islands divers meet them off the deeper drop-offs and open-water sites around Gozo and Comino, most often in the warmer half of the year when bluefin come into the Mediterranean to spawn. Malta also has a large tuna ranching industry, and pens off the coast hold thousands of fish; a handful of operators run dives inside those pens, which is one of the very few places in the world you can do it.