Shark skull. Coloured X-ray of the skull of a mako shark (Isurus oxyrinchus). Its backward-pointing teeth can be seen in the inside of the open mouth. These teeth are continuously worn down and lost, and so must be constantly replaced. This fish's gill plates are at far left and right, with its extremely pronounced conical snout at upper centre. The mako, the fastest swimming shark, lives in tropical and temperate waters worldwide. It is an extremely common shark and feeds on porpoise, swordfish, herring and mackerel. Mako sharks can reach over 3.5 metres in length.