Sharks and chimaeras: large venomous spines

Fin spines, which probably evolved as a means of protection, are generally associated with advanced fishes. However, such spines occur in all three of the living cartilaginous fish groups, but have developed in quite a different fashion in these more primitive groups.

Port Jackson Shark, Heterodontus portusjacksoni
Photographer: Rudie Kuiter. Source: Aquatic Photographics

Among sharks, the Port Jackson (family Heterodontidae) and dogfish sharks (family Squalidae) usually have a single spine at the beginning of each dorsal fin. More than twenty species from these families occur in south-eastern Australian waters, but most live well away from the coastline and are only encountered by professional fishers.

Although only a few of these sharks are known to be venomous, it is likely that all sharks with spines may produce venom. The toxin, contained in the tissue embedded in a groove along the spine, can inflict intense localised pain, swelling, numbness and muscle weakness.

Elephantfish, Callorhynchus millii
Photographer: Rudie Kuiter. Source: Aquatic Photographics

Likewise, the chimaeras or ghost sharks (family Chimaeridae), the elephant fishes (family Callorhynchidae) and the longnose chimaeras (family Rhinochimaeridae) all have a prominent strong pungent spine at the beginning of the first dorsal fin, which is reported to be venomous. Fortunately, only the elephant fish, Callorhynchus milii occurs in shallow water where it is occasionally taken on hook and line in the channels of bays and estuaries.