Also known as foolfish, leatherjackets and shingles, filefish are a curious species of saltwater fish closely related to the triggerfish. They are characterized by their rhomboid shaped bodies, thick, sandpaper-like skin and relatively small, fleshy fins. Filefish also have a long, retractable spine on the base of their head which is often used to lock themselves in place inside caves and crevices, making it harder for predators to fish them out. They are an extremely peaceful, shy species of fish and are also quite hardy in nature. They are excellent choices for most beginner aquarists.