From the Depths: Meet the Knifejaw Fish
500 years ago in Hawaii, before diving masks and fishing rods were invented, native Hawaiians stabbed fish with spears in their hands or used several types of fish traps. They were limited to the fish they could catch in shallow water. Even large fish like the giant trevally or the ulua entered the shallows to feed and were harpooned by the locals, but some fish that live in the deep waters have never been seen by Hawaiians in the ‘era, so they never received a Hawaiian name.
The 150-pound, 30-inch-long, knife-jawed giant fish typically lives in the cooler waters of Kaua’i and O’ahu, but at depths of 100 feet to 1,000 feet deep. This huge, gray-colored fish has a large, rounded body but is only five to six inches thick. It has a huge set of teeth which are fused together and resemble a parrot’s beak. It is sometimes called a breakfast fish or a broom because its large tail fin resembles a broom. Knifejaw fish move quite slowly and feed on hard mollusks like scallops and barnacles that they can crush with their powerful jaws.
Even today, Hawaiian fishermen rarely catch one of these fish because they don’t bite the type of bait commonly used with a fishing rod, but spear fishermen like me will occasionally see some. hide in deep water caves. Knifejaw fish are extremely good to eat and in Japan they catch them with deep-sea fishing trawlers and sell them for a lot of money to serve in high-end restaurants.
I had been scuba diving in Hanalei Bay for over 10 years regularly before seeing any of these weird big fish as they usually live deeper than we can dive into, but in 2018 j saw my fish 40 feet deep. I didn’t even know what the fish was until I videotaped it and sent it to UH for identification. The big Knifejaw fish ate scallops right next to an underwater cliff in Lumahai by placing its lower jaw into the open scallop and then twisting its powerful, massive body to knock the scallop shell off the cliff. He then scraped the tender scallop inside the shell with his powerful scratching teeth. I was quite amazed to watch the whole event!
For the past three years, Knifejaw fish have now entered shallow water for food and many underwater fishermen see them in Kauai and Oahu. At one point, I saw eight of these big fish in a cave 50 feet deep near Sharks Cove, along the north coast of Oahu, where I finally got a good video and photos of it. ‘them.
Why are these deep-sea fish entering shallow water for the first time in 1,800 years here in Hawaii? Is their deep-water food depleted, so they’re looking for a new food source, or do the many Navy submarines that use sonar and electronics offshore scare them in shallow water? Right now we really don’t know but something is changing. All around the Pacific Ocean, where underwater activity is common, deep-sea fish appear in shallow water or have died on the beach, we may need to start investigating this potential problem.
Knifejaw fish are easy for divers to spear because they have that large, flat body and are an easy target. The problem with eating fish is that it can contain the poison of ciguatera fish. The ciguatera toxin comes from the sea urchins Knifejaw feeds on, and sea urchins get the natural poison from the algae they eat. To eat the fish without getting sick, you can take a small bite of the flesh and wait five to six hours to see if it gives you a slight stomach ache. If you don’t have a negative reaction to eating a small piece of fish, the fish is unlikely to have ciguatera. A small amount of ciguatera which is a neurotoxin will not hurt you, but eating a big meal of ciguatoxic fish could require you to stay in the hospital for months!
You can see the Knifejaw fish in action in my underwater educational film The Worlds Guide To Hawaiian Reef Fish on my website at www.underwater2web.com. My educational series on marine life around the world is also available on the web for schools and sustainable ecotourism here in Hawaii.
Terry lilley is a marine biologist living in Hanalei and co-founder of Reef Guardians Hawaii, a non-profit organization with a mission to provide education and resources to protect the coral reef. To donate to Reef Guardians Hawaii, visit www.reefguardianshawaii.org.