Toxic and pharmacologically active secretions from the arabian gulf catfish (arius thalassinus, ruppell)

Arabian Gulf catfish (Arius thalassinus Ruppell) (38), secrete venom from a gland at the base of each pectoral spine, and also elaborate a thick proteinaceous gel-like material from epidermal cells when the fish are threatened or injured. Both of these secretions contain a complex mixture of components which have potent pharmacological effects on test animals. The venom has been thought to play a defensive function in fish survival, but the epidermal secretion does not appear to play a similar active role in predator defense. Both secretions have components with "typical" venom hemolytic and hemotoxic activities. These are not present at levels high enough to cause lethal responses in test animals when injected at levels commonly associated with injuries caused by catfish spines. However, the epidermal secretion contains additional novel protein and lipid constituents, previously unreported in venomous secretions, which confer a lethal activity to this material when it is injected intravenously into rabbits at levels greater than 1 mg protein/kg body weight. Among the constituents of the epidermal secretion are protein and lipid components which induce alterations in cell metabolism, including an abundant lectin, a protein kinase, a large molecular weight clotting factor, a specific hemolytic factor, esterases, prostaglandins, platelet activating factors, and components which induce smooth muscle contraction. It appears that the lethal response noted in test animals results primarily from the induction of a high level of phospholipase activity in blood vessels and blood cells. This activated enzyme causes an unregulated release of arachidonic acid, which is converted to prostaglandins at levels which result in the death of the animals. In spite of the toxic role these individual components play in the overall pharmacological properties of the gel, it can be speculated that the importance of the gel secretion to the fish may lie in aiding wound healing of skin injuries (4).