There are two fish that are commonly referred to as a leatherjacket fish — the Olgoplites saurus and a wide variety of fish in the Monacanthidae family. The former can be found commonly in the Gulf of Mexico and portions of the Atlantic. The latter is usually found near the waters of New Zealand.
The Olgoplites saurus is a fish of the Carangidae family, and it is usually found in the Gulf of Mexico and throughout the Southern portion of the Atlantic coast. It occasionally travels to colder waters though and strays have been spotted and caught as far north as Maine. The fish prefers beaches and waters with reefs and travels in small schools that have been seen to leap out of the water when traveling.
It's coloration is split horizontally, with the top half typically having a bluish tone while its bottom is silver. The fins of the fish are yellow. The most notable characteristic of the fish is its dorsal fin, which is very long and breaks apart, giving the appearance of several small fins covering its spine like the brushes on a comb. These small points are venomous and if pricked by a human can cause very painful wounds. It usually grows to about 10 inches (27 cm) in length and weighs around 10 ounces (287 grams). It is sometimes caught and marketed as a food fish, but it is not very popular as such.
The term "leatherjacket fish" is also used to describe a wide variety of species in the Monacanthidae family of fish that inhabit the waters surrounding Australia and New Zealand. The various species of leatherjacket in the area are often referred to as reef leatherjacket, velvet leatherjacket or smooth leatherjacket fish.
It can vary in size, but most weigh about 1.7 pounds (800 grams) and are around 15 inches (38 cm) in length, although some species are larger. The ocean jackets can grow up to 2 feet (60 cm) and weigh three pounds (1.5 kilograms), while reef leatherjacket fish may weigh close to eight pounds (3.5 kg).
All species share common characteristics and are completely lacking in scales. Instead the fish has a fine skin from which the animal gets its name. All species of the fish also have very large dorsal fins that resemble horns. The fish will commonly prey on small invertebrates, sea sponges and plankton and live in mid-range depths between 65 and 650 feet (20 and 200 meters). Unlike the leatherjacket fish of the Atlantic Coast, these leatherjackets are without venom and mostly harmless to humans.
The various species have been known to bite and peck at the fingers of divers who approach it, but these bites are not serious. It is fished commercially in both New Zealand and Australia and fish bought at low prices in markets can be prepared in a variety of ways including poaching, steaming, grilling and frying.