Marine Poisons: Life and Death

By Karen Steidinger

Part I

"Eat Puffer and Maybe Suffer," the title of a recent article in a conservation newsletter, may get a chuckle or even a hilarious roar, but in reality it is no laughing matter.

Human deaths attributed to poisonous marine animals, particularly fishes, have been recorded since biblical times and some religious laws still condemn eating fish that are finless or scaleless. Figures of scaleless, poisonous fishes have been found on Egyptian tombs. Some early naturalists went further than just recognizing dangerous animals, they actually used marine toxins to remedy ailments. For example, Pliny the Elder (29-79 A.D.) used ground sting ray stingers to relieve the pain of toothaches.

An estimated 500 or so poisonous fishes are inshore species living in warm seas between 45 degrees N and 45 degrees S. Many forms are numerous around small islands in the Pacific. Unfortunately, it is impossible to just look at a fish and tell whether it is poisonous. In some fishes, toxicity is strongly associated with the ripening of their reproductive organs or where the fish lives. Fish toxins are sometimes concentrated in a single organ, such as the liver, muscles, skin, or reproductive organs, or the whole animal may be poisonous.

The best procedure to follow, if you are stranded, starved, and have to eat a fish you know nothing about, is to skin it, remove the head and internal organs carefully, and then soak the remaining meat in water for several hours, throwing away the water before cooking. Many poisons from plants and animals are soluble in water. Often, cooking alone will not destroy or remove the toxic substances. In Japan, finer restaurants have licensed puffer cooks that have been specially trained in preparing puffer for human consumption. Yet the Japanese, even though they are familiar with poisonous fishes, suffer about 100 deaths yearly from puffer poisoning. Puffer poison has the scientific name tetrodotoxin, after the family name for puffer fishes, Tetraodontidae. It can take 10 minutes or 3 hours before symptoms are evident: nausea, vomiting, muscular weakness, paralysis, and respiratory distress. No specific antidote is known.

Puffers, of course, are not the only poisonous fishes. Certain species of snapper, sea bass, barracuda, jack, moray eel, parrotfish, shark, grouper, wrasse, and surgeonfish have also been implicated in human illnesses. Most of these fishes contain one or several toxins, one of which is known as ciguatera toxin. Ciguatera is more famous in Pacific waters; however, in Florida, the red tide organism, Karenia brevis, a one-celled dinoflagellate, and shellfish exposed to blooms of this organism, reportedly have a ciguatera-like toxin that can cause human suffering. Ciguatera poison is thought to originate at the base of the food chain. In Pacific waters, it has been traced to toxic blue-green algae that are eaten by small fishes and, in turn, are eaten by larger fishes. It is through the food chain that the toxin is taken in and accumulated.

The most toxic marine poison known is 160,000 times more potent than cocaine and is produced by several dinoflagellates common to the shores of Washington, Canada, and Alaska. They produce a toxin known scientifically as saxitoxin, or paralytic shellfish poison (PSP). The name saxitoxin has its origin from the Alaska butter clam, Saxidomas, which has caused shellfish poisoning in humans. Again, the association and resultant human distress is through the food chain.

Perhaps other animals of the sea are better known as poisonous and dangerous animals to be avoided. Their effect on man is more direct-by attack. This involves stinging cells or venom glands. The sea wasps or jellyfish of the Austro-Asian area have caused many swimmers pain, scars, and even death. There have been 55 documented deaths attributed to sea wasps since 1963. Physalia, the Portugese Man-of-War, is a jellyfish-like animal known as a siphonophore that periodically causes swimming activity to cease along the Florida east coast and other areas. First-aid stations are set up on beaches to help those suffering from Physalia attacks. Jellyfish and siphonophores have stinging cells called nematocysts in their tentacles, and some Physalia tentacles have been reported to extend 30 feet deep in seawater. Physalia toxin interferes with the conduction of nerve impulses and can cause the heart to stop beating. In addition to poisonous jellyfish and siphonophores, there are poisonous or venomous (having venom glands) cone shells, octopuses, sea cucumbers, sea urchins, marine worms, and other ocean denizens.

In almost all cases, the toxin interferes with the permeability of the nerve membrane and inhibits passage of nerve impulses. The physical effect may only involve nausea, drowsiness, weakness, or vomiting, or it may proceed to paralysis and death. In most cases, a cure is not known; however, a drug called neostigmine has been successful in the treatment of barracuda poisonings. Some human illnesses attributed to eating fish are caused by decomposing bacteria and are common among jacks, skipjacks, and oceanic bonito; however, symptoms usually subside within 12 hours.

It is estimated that 30,000 human illnesses from eating poisonous marine animals, primarily fishes and shellfish, occur each year, some of them resulting in death. With figures like that, the title of the article "Eat Puffer and Maybe Suffer" should be taken seriously.

Part II

Yes, poisonous marine animals can kill people, but unbelievable as it may sound, they can save lives too. Natural products from land plants have been used for years as antibiotics, narcotics, analgesics, anti-leukemia agents, and other drugs in the treatment of human distress. Why not use products from marine plants and animals as drugs? After all, poisons from marine animals show potential in the treatment of hearing diseases, intestinal troubles, infections, tumors and other ailments.

One of the biggest problems is money. It takes approximately 7 million dollars to develop a drug before it is submitted to the federal Food and Drug Administration and then only 1 out of 2,500 drugs submitted reach the commercial market. Another problem involves the collecting and harvesting of suitable marine organisms. If the chemical structure and properties of the poison are known, then scientists can artificially recreate the substance and need not worry about how many animals they have to collect. Prior to the 1960s, little was known about the chemical makeup of marine toxins, but now that scientists have unraveled the chemistry of these poisons, synthesis of these potential drugs is possible.

There is one outstanding use of a marine poison as a drug-puffer poison is being used as a narcotic for terminal cancer patients in Japan. Perhaps the Japanese, because they are surrounded by the sea and depend on it so desperately for food, are more attuned to its resources. The Japanese also found that a certain acid in the brown seaweed Digenia is a valuable drug in the control of tapeworm, whipworm, and roundworm. There are many natural compounds of seaweeds that show antibacterial, antifungal, and antiviral activity. However, these are not poisons, rather they are often components of the cell walls or byproducts of everyday functions. Ironically, some poisons are thought also to be the byproducts of everyday functions, particularly among the one-celled organisms.

One product of marine seaweeds, although not of a poisonous nature, deserves attention because of its potential anti-tumor and anti-leukemia activities in animals exposed to radiation. Sodium alginates of seaweeds tend to inhibit the absorption of radioactive strontium in the bloodstream and bone tissue of rats by 75 percent.

To cite examples of potential uses for poisons or toxins often involves using the effect of the poison as the cure. For example, ciguatera poison, which affects the neuromotor system, can relax spasms when administered in small doses. Another poison isolated from an electric eel shows potential as an antidote for pesticide poisoning.

These are only a few examples, but they are enough evidence to support research on potential drug sources from the sea.