Common names: Bull-head shark, Bullhead shark, Japanese Bullhead shark, Port Jackson shark, Cestracion shark, Cat shark.
The Japanese Horn shark has, like all Heterodonts, a distinctive appearance, unmistakeable from all other species.
The body has the typical rounded, solid head with a smiling rictus. Inside the mouth are the two types of teeth, front pointed holding teeth and rear flat grinding plates, that give this family ofJapanese Horn Shark (Heterodontus japonicus) Juvenile colour pattern. sharks their order and family names: heteros (different) and odous or odont (teeth).
The nostrils are very large allowing the olfactory organs to process large volumes of water. It does not take much bait in the water to lure a resting Horn shark out of their daytime resting spots. The large nostrils provide ample input during nocturnal foraging.
The snout, when viewed front on, gives this species a pig-like appearance. The five gills pairs Japanese Horn Shark (Heterodontus japonicus)are flushed by muscular contractions, allowing this shark family to rest for long periods of time out of ocean currents.
The eyes are relatively small, without nictitating eyelids, surmounted by bony crests. Behind the eyes are small spiracles through which water can be drawn and pumped over the gills.
The pectoral fins are proportionally large, allowing the shark to be highly maneuverable and also providing a steady base on which to rest in heavy surge conditions. There are two large, tall, slightly backswept dorsal fins which may be quiet falcate (sickle-shaped) in adults. Both fins have a sturdy spine on the anterior (front) edge, roughly 1/3 to 1/2 of the height of the dorsal fin. There are a pair of pelvic fins under the mid point between the dorsal fins and an anal fin behind and below the second dorsal fin. The tail is large, paddle-like, with a large subterminal notch.
Overall the body is cylindrical, tapering quickly behind the pectoral fins to a narrow caudal peduncle. The overall impression is a shark with oversized fins and a big, blocky head.
Body colour is pale tan to golden brown with a series of dark broad bands interspersed with narrow lighter stripes.
Japanese Horn sharks are found not only in Japan but also Korea, Taiwan and China. While that may seem to be a broad area of distribution, compared to free swimming shark species, the bottom dwelling horn shark species have a very limited distribution range.
Their preferred habitat is rocky kelp covered reef from the shallows to about 40m deep. Most often they are found in 10+m of water.
Diet consists of small fish, crustaceans, molluscs (shells and octopus) sea urchins and various sessile animals. Using their very large, sensitive nostrils, they track down their prey then pry the animal off the sea bed using their pointed front holding/gripping teeth then crushing into pulp with the flat grinding plates. This species has jaws that are very extendable, useful for sucking in prey from among thick reef covering.
They may swim above the reef while moving between feeding or resting areas but will also waddle or hop along the sea bed using their large pectoral and pelvic fins.
Females are oviparous, laying leathery egg capsules with a spiral flange that encircles the case 3 times. The tip of the conical egg has a pair of short tendrils. Eggs may be deposited in a communal “nest”, although the mother’s provide no continued care after laying. Two eggs are deposited each time, with 6-12 layings over the March to April (sometimes extending to September) laying season. Eggs and egg collections are usually found in the 8-10m depth range.
The eggs mature over about 12 months with the young pushing out of the larger end of the case. At hatching they are about 18 cm long, growing to 70 cm at sexual maturity then on to a maximum length of 120 cm.
Juveniles are more brightly patterned, have proportionally much larger fins and are pretty cute.
This is a species is often displayed in aquariums due to their hardy bottom dwelling nature, strange appearance and ease of care. In Japan, aquariums are hugely popular, with massive structures able to house all sorts of sharks including the largest fish of all, the Whale shark (Rhincodon typus).
Etymology: Heterodontus from the Greek, “heteros” meaning “the other of two, other, different” and the Greek word, “odous” meaning “teeth”. Then japonicus, referring to the location of the originally described specimen. So, “from Japan, with two different types of teeth”.