A shark that exhibits sexual dimorphism

The Narrowmouth catshark (Schroederichthys bivius) is a catshark belonging to the family Scyliorhinidae, found from central Chile around the Straits of Magellan, to Argentina. Their water depth ranges by location. Males are longer and slenderer than females, and both sexes have strikingly beautiful patterns.


Family: Scyliorhinidae – Catsharks

Genus: Schroederichthys 

Species: bivius


Phylum– Chordata

Class– Chondrichthyles


Common NameGround Sharks

Family– Scyliorhinidae

Common NameCatsharks




Average Size and Length: Hatchlings measure between 14-20 cm/5.5-7.9 inches. Mature males measure at 53 cm/1.7 and mature females at 40 cm/1.3. The maximum recorded for a male has been 82 cm/2.7 feet, and 70 cm2.3 feet for a female.

Teeth and Jaw: The Narrowmouth catshark displays heterodont dentition or dental sexual dimorphism. Adult males have much longer and narrower mouths than females. Adult males have much larger teeth than females; the teeth are twice the height. The cusps seem long and pointed, and somewhat thick, with almost the appearance of two miniscule cusplets surrounding the main cusp in the middle.

Head: The snout is short, narrow and rounded. The anterior nasal flaps are narrow and lobate.

Tail: The tail is short.

Demographic, Distribution, Habitat, Environment and Range: The Narrowmouth catshark can be found in the southeast Pacific and southwest Atlantic in southern Chile to southern Brazil from central Chile around the Straits of Magellan, to Argentina between latitudes 23° S and 56° S. They can be found in temperate waters on the continental shelf and upper slope between 46-1,178 feet. They are mostly found less than 427 feet. In the south, they are found in deeper water. They are considered demersal.

Diet: In the Beagle Channel in the summer, they feed mainly on squat lobsters. They will also feed on crustaceans and small fish, and in other locations their diet will vary.  

Aesthetic Identification: The Narrowmouth catshark has a fairly slim body with seven or eight dark brown saddles on a grey-brown back, scattered large dark spots not bordering the saddles, and there are usually small white spots. There are two conspicuous saddles in the interdorsal space. The first dorsal fin origin is slightly in front of the pelvic fin insertions. Adult males are longer and lighter than adult females. The young are even longer and slenderer, but as it grows its proportions change and it becomes rather more thickset.

Biology and Reproduction: They are oviparous, and probably lay pairs of egg cases, one per oviduct. They lay them in sheltered nursery grounds. The egg cases have tendrils which can attach to the sea bed.

Behavioral Traits, Sensing and Intelligence: Not much is known about their behavior.

Narrowmouth Catshark Future and Conservation: There is not enough data to evaluate, but they may possibly be declining. The only place at which egg cases have been found is the estuary of the Deseado River in Argentina, and none have been found there for a number of years, perhaps reflecting an increased level of noise and disturbance by vessels using it as a port.

Narrowmouth Catshark Recorded Attacks on Humans: Not a threat to humans.