When going to the beach on May Day, this guide to avoiding "toxic substances" on the beach is essential!

The May Day Golden Week is coming soon, and I believe many friends will choose to go to the beach as an important travel choice. However, when going to the beach, you may sometimes encounter some dangerous creatures that you don't know.

Not long ago, several tourists discovered more than 20 translucent jellyfish that looked like plastic bags and had a beautiful blue body color while visiting a beach in Wencheng Town, Wenchang City, Hainan Province. However, experts later reminded that these beautiful-looking little jellyfish were actually poisonous Portuguese man-of-war, and should never be touched casually.

When we play at the beach, we may encounter many inconspicuous or seemingly beautiful and cute creatures, but we don’t know how terrible they are. Let’s start with the Portuguese man-of-war jellyfish and help you identify several common “poisonous creatures” that appear on the beaches of my country, so that you can spend a good time at the beach safely.

01 Portuguese man-of-war

The Portuguese man-of-war is widely distributed in tropical and subtropical waters of the Pacific, Indian and Atlantic Oceans. It is also distributed in my country's East China Sea and South China Sea. For example, there is a chance of encountering it in Hainan mentioned in the news, as well as the coasts of Guangdong, Guangxi and Fujian.

The Portuguese man-of-war is relatively easy to identify. It belongs to the order Siphonophore of the class Hydrozoa. Compared with most jellyfish we are familiar with, such as moon jellyfish and jellyfish, which belong to the class Scyphozoa ( appearance characteristics : the jellyfish body has an umbrella-shaped or bowl-shaped cap and multiple tentacles surrounding the mouth ), its "appearance" is alternative - it does not have a cap like that of a Scyphozoan, but has a gas-filled top sac formed by a special polyp on the top.

Portuguese man-of-war jellyfish off the coast of Pajara, Fuerteventura ( Image source: Wikipedia )

What tourists see as "plastic bag-like" things is the Portuguese man-of-war's floating bladder. The Portuguese man-of-war does not have the ability to swim actively, and relies on this bladder to float on the surface of the warm ocean and drift around with the ocean current, but sometimes it is washed onto the beach by waves. The name "Portrait of the Portuguese man-of-war" comes from the shape of its floating bladder.

The toxicity of the Portuguese man-of-war comes from the tentacles under its buoyancy bladder. These slender tentacles are usually retracted under the buoyancy bladder, but can stretch to 10 or even 30 meters long when hunting. They are covered with toxic stinging cells. If a swimming human accidentally touches the tentacles of a Portuguese man-of-war jellyfish, he or she will be stung by its stinging cells, leaving thin, red and swollen scars like whip marks on the skin, causing severe pain like burns or bee stings, and may even lead to severe allergies or even life-threatening.

Therefore , if you see a beautiful blue "plastic bag" floating on the water while swimming, do not approach it. A one-piece swimsuit can also prevent being stung by the tentacles of a Portuguese man-of-war to a certain extent. When you encounter a Portuguese man-of-war washed ashore by the waves, do not touch or pick it up with your bare hands .

Fortunately, most of the Portuguese man-of-war distributed along the coast of China are small in size and less toxic than their Atlantic relatives. If you are unfortunately stung, you can moisten the wound with vinegar (or 5% acetic acid solution) , and then soak the wound in 45 degrees Celsius hot water for 45 minutes ; the slender tentacles of the Portuguese man-of-war are very easy to break, and the broken tentacles may still be attached to the victim and continue to sting. The above measures can kill the stinging cells on the broken tentacles in the shortest time and avoid further damage. After initial treatment, you should go to the hospital for treatment as soon as possible .

02 Distant relatives of Portuguese man-of-war

Distant relatives of the Portuguese man-of-war, which belong to the subphylum Medusa, also have densely packed venomous stinging cells on their tentacles. If you touch them carelessly, you may be stung. In China, the species that are more likely to hurt people are the jellyfish and the genus Nebula . Both types of jellyfish are large in size, and severe stings can cause systemic symptoms or even be fatal . Therefore, when swimming in the sea, you should try to stay away from any type of jellyfish you see , and do not touch or pick up jellyfish stranded on the beach at will. In particular, you should pay attention to avoiding the tentacles around their mouths. If you accidentally come into contact with a large number of jellyfish tentacles and suffer severe stings, you should rush to the hospital for treatment as soon as possible.

Genus Cynomorium (Image source: Wikipedia)

Jellyfish at the Monterey Bay Aquarium (Image source: Wikipedia)

Sea anemones are cnidarians, the same animals as jellyfish. Some species of sea anemones are capable of stinging human skin. If you encounter any type of sea anemone while visiting the beach, especially large ones, do not touch them with your hands.

03 Marine fish with poisonous spines

Some marine fish with poisonous fin spines may sting humans and cause poisoning or even life-threatening. The dorsal fins and pectoral fins of fish in the family Catanidae and Anguilla, as well as the dorsal fins of fish in the genus Bluefin (commonly known as "fox", "mud fierce", "Golden Valley Man", etc.), Golden Drum (commonly known as "Golden Drum") and the suborder Eriocheir (commonly known as "Stone Nine Gong", "Lion Fish", etc.) all have sharp fin spines and venom glands. If a person is accidentally stung, it will cause redness, swelling, severe pain or even more serious poisoning reactions .

(1) Catanidae and Anguillae

The appearance of the sea catfish is similar to that of the catfish or yellow catfish in freshwater, and the spines on its pectoral and dorsal fins are poisonous. The eel catfish, which also belongs to the order Siluriformes, has a slender tail like an eel and an overall appearance like a large tadpole. The more common eel catfish in China is the line-striped eel catfish, which has a black back and two yellow-white vertical stripes on the sides of its body. They often swim in groups, and their fin spines are more toxic than those of the sea catfish. Both are distributed in the East China Sea and the South China Sea in China, and their stings can cause prolonged severe pain and cramps . If you catch these two types of fish while fishing, you must be careful to avoid stings when handling them . If the sting is serious, you need to go to the hospital for treatment to avoid wound infection .

Line-lined eel catfish (Image source: Wikipedia)

( 2 ) Bluefish

Including many common edible fish (such as brown bluefin fish commonly known as "mud meng" and "stinky belly", star-spotted bluefin fish commonly known as "Jinguman" and "Huannimeng") and marine ornamental fish (such as fox bluefin fish commonly known as "yellow fox"), which are more common in shallow seas and harbor estuaries with many reefs in the South my country Sea and the East China Sea. The dorsal and anal fin spines of bluefin fish are poisonous. Although the toxicity is not as severe as that of eel catfish, it can also cause pain and redness and swelling. If you catch it, you should avoid being stabbed when handling it. If you are stabbed, you should also properly treat the wound to avoid infection.

A group of young brown-blue fish in Longdong Bay in northeastern Taiwan are nibbling algae on the reefs in the shallow sea. The body color of brown-blue fish is yellow-green when they are young. (Image source: Wikipedia)

Star-spotted bluefin mullet ( Image source : Wikipedia )

Fox blue fish (Photo source: Wikipedia)

( 3 ) Golden Money Fish

Commonly known as "Golden Drum", it is common in the coastal shallow waters, harbors and estuaries of the South my country Sea and the southern East China Sea. It also enters freshwater. Due to its elegant body shape and beautiful body color, it is often kept as an ornamental fish. Like the blue fish, the dorsal and anal fins of the golden coin fish are also poisonous. The sting will also cause severe pain and redness and swelling. If caught, the treatment method is the same as that of the blue fish.

Money fish (Image source: Wikipedia)

(4) Odontocephalus (stonefish, tiger fish)

Among these ray-finned fish with poisonous spines, the most dangerous are the members of the genus Mylophobiosus. These fish are commonly known as "stone fish" and "tiger fish" along the southern coast of China. They are not good at swimming and often rely on their body shape and protective coloration that are very similar to sea reefs to hide in the seabed and intertidal zones of shallow coastal waters. They prey on small fish and invertebrates, and are difficult to find even with careful observation. The first dorsal fin of the mylophobiosus has 12-14 sharp fin spines connected to the venom glands. If a person accidentally steps on the mylophobiosus while swimming or wading, he or she can easily be stung by it. The venom can cause severe pain, convulsions, paralysis and local tissue necrosis, as well as difficulty breathing and disruption of the body's blood circulation . In severe cases, it can even be fatal. There have been records of mylophobiosus injuring and killing people in Australia and Japan.

The poisonous catfish is only found in the South China Sea, along the coasts of Guangdong, Guangxi, Fujian, and Hainan . When wading between reefs at the seaside, you should wear slippers or water shoes to avoid going into the water barefoot . If you are accidentally stung by a poisonous catfish, you must go to the hospital for treatment as soon as possible.

Rose poisonous scorpionfish (Image source: Wikipedia)

(5) Stingray

This is a type of cartilaginous fish that can stab humans, also known as the "devil fish". It has a wide and flat body and a slender tail. It often swims on the seabed with its pectoral fins in a wave-like motion, or buries itself in the sand. Its tail has one or more large and sharp fin spines, with many backward-bending serrations on the edges. The surface of the fin spines is also covered with mucus mixed with toxic secretions. Stabbing can cause huge penetration and lacerations, leading to severe pain, swelling and muscle spasms. If it stabs important organs or aortas, it may cause more serious consequences or even death .

Short-tailed stingray (Image source: wikipedia)

In 2006, Steven Irwin, a famous Australian crocodile hunter, died while filming a show after a huge short-tailed stingray pierced his chest and heart. In 2018, a man in Taoyuan, Taiwan Province, died after a red stingray he caught pierced his arm. Stings from stingrays often cause serious bacterial and fungal infections in the later stages.

Common stingrays in China include red stingrays and yellow stingrays , which are distributed in the South China Sea and the East China Sea . Like poisonous fish, stingrays will not actively attack humans. Accidents of stinging humans are often caused by people wading in the water failing to find the stingray lurking in the sand, accidentally stepping on it, or being caught and disturbed by people, and then acting out of self-defense. Just like preventing poisonous fish, you should avoid swimming barefoot in waters where stingrays are present. If you see a stingray, don't chase or tease it to avoid it from hurting people . Tiger sharks, which belong to the same cartilaginous fish family, also have poisonous spines on their dorsal fins. Although they are not as dangerous as stingrays, being stung can also cause redness, swelling and severe pain. If you encounter or catch one, you should also be careful to prevent being stung.

Red stingray (Image source: wikipedia)

Finally, I wish you all a happy May Day holiday in advance!

Author: Hu Kai, science research instructor, CCTV-9 documentary channel science consultant

Reviewer: Liu Qinghua, Researcher, Institute of Oceanology, Chinese Academy of Sciences

Produced by: Science Popularization China

Produced by: China Science and Technology Press Co., Ltd., China Science and Technology Publishing House (Beijing) Digital Media Co., Ltd.