Jackknife fish or Equetus lanceolatus are members of the family Sciaenidae more commonly referred to as the drum family. This species is endemic to the western Atlantic and the Caribbean Sea.

This distinctive looking creature’s name is a direct reference to its unique shape. Its elongated dorsal fin and slender tail region give the fish’s body the general shape of the letter U resembling a half opened pocket knife. Their extended dorsal fin has also lead to the fish being called a highhat. This species has three evenly spaced black vertical bars on its body. Juveniles are yellow and black. As the fish matures it will loose its yellow coloration. Adults have silver bodies. This is not a particularly rare fish. Despite its exotic appearance, this species is not commonly found in home aquariums.

The jackknife is a relatively large fish. It will reach up to 10 inches in length as an adult. A minimum tank size of 55 gallons is recommended to provide it with adequate room. A 75 gallon tanks is considered ideal. This is a very timid, peace loving creature and will require plenty of hiding places if you intend to raise one in a community setting.  It may very well remain hidden from its tank mates until it builds up the confidence to venture out into its new surroundings. Housing it in a refugium will help make it feel more secure and reduce its general stress levels upon initial introduction. Despite its demean nature this fish will demonstrate moderate territorial behavior towards members of its own species. This can be minimized by adding more than one of this species to their new surroundings simultaneously. This species is not a suitable candidate for a marine reef aquarium. Its diet in its natural habitat consists of many of the inhabitants typically found in a reef tank. It will view your ornamental crustaceans as a source of nutrition.

Jackknives are carnivorous. Getting them to start feeding when they are newly captured can prove problematic. They may be traumatized. Or there is a distinct possibility that they simply don’t recognize marine fish foods as a source of nutrition. Providing the fish with dietary choices similar to what it would eat in nature will aid in its acclimation. Offering it live brine shrimp or bloodworms may tempt it to start eating. Having an adequate supply of living rock will also simulate its native feeding grounds.  It will eventually figure out that frozen products, pellets and flake food developed for marine carnivores are a legitimate food source. Chopped fresh sea food such as shrimp and squid will help provide a well balanced diet. 

In the wild, these fish comb through the sandy ocean floor in search of fireworms and polychaete worms. A sand substrate will prevent this creature form accidentally inflicting injury upon itself.  Living sand will provide it with a natural source of nutrition similar to what it is accustomed to eating. Remember this is a skittish creature. You will want to avoid mixing it with more aggressive species and forcing it to compete for its food.