The Jack-knifefish (Equetus lanceolatus), is a black and white/silvery fish which belongs to the Sciaenidae family, the drums category.  It is a Carribean reef fish and can be found in the Carribean, Bahamas, Florida, and the Gulf of Mexico.


Photo by Barry Peters is licensed under CC BY 2.0. This is a juvenile Jackknife fish.


Morphology deals with the size, form, shape, and structure of organisms. The Jack-knifefish is a fairly small fish ranging from about 5-9 inches in size (12-23 cm). It has an elongated dorsal fin with a black band that runs from the tip of the dorsal fin to the end of the tail, which helps identify this exotic looking fish. They are an odd-shaped fish and have considerably long dorsal and caudal fins. The combination of those two fins resembles a jack-knife, giving it it’s a common name, the Jack-knifefish. This odd trait is more present in a juvenile jackknife fish than older jackknife fishes.

General description and Behavior

The Jackknife fish is a shy and graceful saltwater fish, so they require a peaceful environment with a sandy bottom and plenty of places/rocks to hide in. They feed on inhabitants of reefs like ornamental shrimps, polychaete worms, and even other small reef fishes; because of this, I think it’s safe to say that they are carnivorous benthic feeders.

The odd shape of the Jackknife fish actually serves as a kind of protection from predators by confusing them into thinking that it is two different fishes, rather than one. The coloration of the jackknife fish may also serve to hide the eyes so that predators cannot tell where the fish is looking, and even confuse the predators into thinking maybe it’s not even a fish.

The information in this chapter is thanks to content contributions from Malisa Rai


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A Student's Guide to Tropical Marine Biology Copyright © by by Keene State College Students, BIO 381 Tropical Marine Biology is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.

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