Atlantic sailfish (Istiophorus albicans) hunting sardines in the Caribbean sea. They have a large dorsal fin which has the appearance of a sail. The fin runs along the length of its body and, when extended, it is taller than the width of the body. The Atlantic population of the sailfish is sometimes referred to as Istiophorus albicans, while the Indo-Pacific population is called Istiophorus platypterus, but there is no genetic evidence to indicate they are two separate species

Photograph: Doug Perrine/Alamy