Jackknife Fish ©Melinda Riger @ GB Scuba


The rather uncomfortably ‘double-k’  Jackknife fish is one of 3 types of similar drumfish subspecies of Equetus found in Bahamas waters. The others are the High Hat and the SPOTTED DRUMFISH – the first fish featured in this series. Each of these drumfish species has juveniles that are elegant and delicate, becoming more conventionally fishlike as they grow to adulthood, as the final image shows.

Jackknife fish (juv) ©Melinda Riger @ G B Scuba copy

I always want to stick a hyphen in to separate each k: jack-knife fish. I think it’s an English thing. I have seen, at the other extreme, ‘jack-knifefish’, which looks most weird of all. Checking online, jackknife fish wins by a distance as the correct spelling. 

Jackknife Fish (juv) ©Melinda Riger @GB Scuba

These little fish, typically between 6 and 9 inches, inhabit the coral reefs of the Caribbean, the Gulf of Mexico, Florida and the Bahamas. Juveniles eat plankton and similar organism, graduating to small crabs and shrimps as adults.

Jackknife Fish ©Melinda Riger @ G B Scuba

A FULLY GROWN JACKKNIFE FISH (NOAA)Jackknife fish adult_NOAA_Photo_Library

Like other drumfishes, the jackknife can produce ‘croaking’ or ‘drumming sounds. This involves the fish beating its abdominal muscles against its swim bladder. There’s a lot more to it than my rather simplistic summary, but it’s probably as much as anyone needs or wants to know… The primary reason is believed to relate to mating. Other reasons include ‘low-level aggression’, and keeping in touch with each other in turbid waters.  I prefer the unscientific theory that sheer happiness makes them croak. Here’s a short video of a happy juvenile Jack knife fish (that’s yet another spelling variant…)


Credits: Melinda Riger / GrandBahama Scuba; NOAA



This post is the first of a planned series on Bahamian reef fish. Those who follow this blog (I thank you both) may recall with horror (or worse, pity) my own efforts with reef fish, using a tiny cellphone-sized video camera.  Misty stills culled from video footage. Enthusiastically wobbly movies as I struggle to swim and breathe simultaneously in an alien element. I am more underwater CLOUSEAU than COUSTEAU. However, thanks to Melinda Riger, who with husband Fred runs GRAND BAHAMA SCUBA, I have kind permission to borrow and display images from her stock of wonderful reef fish photographs.

The spotted drum fish (related to two other Caribbean drumfish, the High-Hat and the Jack-knife fish) belongs to a large worldwide family, the Sciaenidae. Besides other drum varieties, the family includes ‘croakers’. These species are all named for the repetitive throbbing or drumming sounds they make. This involves the fish beating its abdominal muscles against its swim bladder. If I find out the reason for this (Species communication? Food call? Alarm? Warning? A piscine ‘advance’? Happiness?) I will add it here in due course. Here an example of an atlantic croaker from the excellent DOSITS site (Discovery of Sounds in the Sea)

[audio http://www.dosits.org/files/dosits/croaker48.mp3]

The spotted drum is one of the few fish of the species to inhabit coral reefs – most are bottom-dwellers (often in estuaries), avoiding clear water. These fish tend to be nocturnal feeders, feeding on small crabs, shrimp and small invertebrates. As far as I can make out they are solely (or primarily) carnivore, and do not graze on algae of other reef plant life.



The photos above are of adult spotted drums. The ones below are of juveniles, and show the remarkable growth-pattern of these fish, from the fragile slender creature in the top image, through the intermediate phase of the one below it (with the amazing brain coral), to the striking adult versions above. People like to keep these pretty fish in aquariums; fine, I’m sure there are plenty to go round, but these ones look pretty happy to me in their natural reef environment…

Juvenile Drum Fish (pre-school)Juvenile Drumfish 2 ©Melinda Riger GB Scuba

Juvenile drum fish (school-age)

Juvenile Drumfish ©Melinda Riger GB Scuba(Header image credit: Wiki-Cheers)

Finally, I’ve just come across this short video from a “Florida Aquarium”, showing how these fish swim. It rather looks as though it has been fin-clipped for some reason… or just damaged, maybe

[youtube http://www.youtube.com/watch?v=dqEWqfLeqOw]