When we hear of venomous animals, we will, most likely, immediately think of snakes. But, did you know that thousands of fish species are also venomous, capable of inflicting severe pain? Even more interestingly, separate teams of scientists are endeavouring to find out how we can use specific fish venoms to treat pain, cancer, and other medical conditions.
3,000 Fish Venoms
Investigating fish venoms is still a new area of research. Given that around 3,000 species (7-9% of fishes) are estimated to be venomous, this subject area appears to be promising.
Venomous fishes have been spotted in both freshwater and marine environments: from stingrays, catfishes, and stonefishes, to the famous aquarium fish, fang blenny.
Some of these fishes can inflict great pain. Venom researcher Bryan Fry from the University of Queensland, Australia, attests to how true this can be: he narrates of an incident whereby he was stung by a stingray. According to Fry, the pain was “immediate and blinding”.
Painkillers from Fish Venoms?
Another scientist looking into fish venoms, biologist Leo Smith from the University of Kansas, relates how some people use the spines of two fish species, namely the chilipepper rockfish, and the California shortspine thornyhead, to stab themselves, believing that the venom would reduce their arthritic pain. While there is no evidence of pain alleviation in rockfish venom, it is believed that examining how fish venom triggers pain might assist researchers in understanding the way in which nerve cells perceive pain—this will, in turn, help them to concoct new ways to relieve people of pain.
Fish Family Tree
Smith’s efforts to understand fish venoms led him to draw a fish family tree. His findings are published in the Journal of Heredity. His research is helping scientists to determine which fish species are venomous to, ultimately, be able to decipher the nature of the venoms.
Another finding from Smith’s work is that fish venom evolved several times down the line: this happened much more than what is documented in snakes (only once) and bees. Smith explains that non-venomous fish evolved a venom-releasing mechanism 18 different times throughout history. Commenting on Smith’s findings, Fry says that the multiple evolution of venom within one group is “extraordinary”.
How do Fish Release their Venoms, and Why?
Fish venoms originating separately is consistent with the fact
that the fish venoms are released in varying ways from species to species. Some have spines with venom glands located in fins on the back of the fish. Others, like catfishes, the venom glands are found in the pectoral fins. A paper published in the Biological Journal of the Linnean Society describes the evolution of venom delivery structures in catfishes.
Yet others, like the weever fish, have their spines at the operculum, near the gills. Stingrays have theirs over the tail. Fang blennies bear their venom glands at their lower canines.
Despite this great variation, the effect of the venom remains mostly the same, which is to counter an attack from predators. As a consequence, pain is generated from the venoms, some of which might numb the site of delivery on the victims. The latter will all have their cardiovascular system affected: mostly, the blood pressure is decreased, a way to surprise and weaken a predator. Now, if you, a human, are stung, the signs will range from itching, skin reddening, swelling, to localised paralysis, lowered blood pressure, and weak breathing; some of these can be fatal.
The reef stonefish pictured above can also kill you. If it is distressed, its set of 13 spines adjacent to venom glands will protrude from its back, and the toxins released are potent enough to kill a human.
Medicines to Lower Blood Pressure
Further discoveries revealed that the chemical weaponry behind fish venoms exists in a great variety. According to the scientists, the potent molecules making up the venoms might help them to produce medicines. For instance, a new study has shown that a venom seems to act on opioid receptors; apparently, the fishes stupefy their victims. Sounds very Harry Potter-like, right?! As the venom works on these receptors, the scientists believe it might act as a sedative. According to Fry, a victim would feel stoned. Other effects generated are a lower blood pressure, and disorientation and dizziness.
Other venom molecules have greater implications. Some appear to delay cell division, and others are balms to inflammation: this might take scientists beyond making just pain-killers.
The weever fish has been found to blacken and kill tissues. When a team from University of Tübingen, Germany, tested the venom on red blood cells, they observed that it made the cells shrink and die. They, thus, tested it on cancer cells as well: the latter stopped growing, and eventually died. The paper is published in Scientific Reports.
The next step is to now identify the compounds in the venom that triggers cell death. It is hoped that the weever fish venom might be used to make an anti-cancer drug.
Medicines from Venoms
Medicines from venoms are not something new. This has been done in the past. For instance, a blood pressure drug named captopril (Capoten) was based on a pit viper. Another one is a painkiller developed from a marine cone snail’s powerful venom.