Fig. 135.—Brown Tang, Teuthis bahianus (Ranzani). Tortugas, Florida.
The Lancet of the Surgeon-fish.—Some fishes defend themselves by lashing their enemies with their tails. In the tangs, or surgeon-fishes (Teuthis), the tail is provided with a formidable weapon, a knife-like spine, with the sharp edge directed forward. This spine when not in use slips forward into a sheath. The fish, when alive, cannot be handled without danger of a severe cut.
In the related genera, this lancet is very much more blunt and immovable, degenerating at last into the rough spines of Balistapus or the hair-like prickles of Monacanthus.
Spines of the Sting-ray.—In all the large group of sting-rays the tail is provided with one or more large, stiff, barbed spines, which are used with great force by the animal, and are capable of piercing the leathery skin of the sting-ray itself. There is no evidence that these spines bear any specific poison, but the ragged wounds they make are always dangerous and often end in gangrene. It is possible that the mucus on the surface of the spine acts as a poison on the lacerated tissues, rendering the wound something very different from a simple cut.
Fig. 136.—Common Filefish, Stephanolepis hispidus (Linnæus). Virginia.
Protection Through Poisonous Flesh of Fishes.—In certain groups of fishes a strange form of self-protection is acquired by the presence in the body of poisonous alkaloids, by means of which the enemies of the species are destroyed in the death of the individual devoured.
Such alkaloids are present in the globefishes (Tetraodontidæ), the filefishes (Monacanthus), and in some related forms, while members of other groups (Batrachoididæ) are under suspicion in this regard. The alkaloids produce a disease known as ciguatera, characterized by paralysis and gastric derangements. Severe cases of ciguatera with men, as well as with lower animals, may end fatally in a short time.