7 Dangerous freshwater fish (you should know)

In this post, we will meet a few of the most dangerous freshwater fish. We will also outline their biology and ecology.  

Dangerous freshwater fish

The most dangerous freshwater fish are: 

–       Tigerfish;

–       Siluro/Wels catfish;

–       Porac/Electric eel;

–       Piranha;

–       Candiru/Toothpick fish;

–       Pirarucu;

–       Goonch fish;

–       Payara/Vampire fish;

–       Giant Freshwater Stingray.

Tigerfish

There are many Tigerfish species. Their name come from their fighting behaviour when captured and also due to their predatory habits and appearance. The Tigerfish inhabit African freshwater environments and are very admired.

They have dark horizontal stripes on their body. The number of stripes varies with the species, from one to many. They have dagger-shaped teeth that are projected out of the mouth when closed.

The Goliath Tigerfish is the biggest species of this group. Its average length is 1,8 metres and weighs up to 60 kilograms. The most common Tigerfish species is the Therapon jarbua, it has three stripes. This species has around 30 centimetres long and extremely sharp spines on its operculum. 

Siluro/Wels catfish

The Siluro, or Wels catfish, is another gigantic catfish species. This species is native to Central and Eastern Europe deep slow-moving rivers and lakes. However, it was introduced to Western Europe and can also inhabit coastal areas. 

Silurus can grow up to 5 metres long and weigh over 200 kilograms. They have chemoreceptors and a Weberian apparatus. These structures are responsible for smell and acoustic perception, thus, they support hunting behaviours. The hunting behaviour is also associated with the use of pectoral fins to disorient the prey, which is swallowed entirely.

Due to their huge size, weight, and sharp teeth, they can be harmful to humans. The attacks on humans are not so rare. However, they are generally not associated with deaths. Few rare cases reported attacks to humans where no remains were found or the Siluro ate the prey partially.

Porac/Electric eel

The Porac is an electric eel. This fish is extremely dangerous and inhabits streams and lakes in the Amazon and Orinoco Rivers. Its colour is brownish-grey, sometimes with a reddish belly. They can grow up to 2.75 metres and weigh up to 22 kilograms. 

Porac fish are extremely predatory and can release a massive electrical discharge as a hunting strategy. They have around 6,000 electrocytes through their bodies, which are responsible for electric generation. This electric discharge reaches a maximum of 860 volts. In the case of humans being in the water, this shock would result in heart failure.

Evolutionarily, the electric discharge may have evolved as a manner for the Porac to swallow the whole prey directly to the stomach and avoid any type of wounds in the mouth. Also, this discharge could be a way to reduce the energy costs of hunting by making the prey slower, and thus, reducing chasing necessity.

Piranha

Piranha is one of the 60 carnivorous daggle-shaped teeth species inhabitants of South American rivers and lakes. They earned an unfair amount of fame due to the Piranha movie from 1978. 

Most of the piranha species grow up to 60 centimetres. Their colour varies from completely dark brown to silver with an orange belly. Piranhas have very strong jaws with a bite strength of 25 to 30 times their body weight.

They inhabit waters from Argentina to Colombia. However, they are more diverse on the Amazon river, where it is possible to find around 20 different species. They normally feed on fish, crustaceans, and sometimes on plants and seeds. Although, during food scarcity periods, they commonly attack anything. Thus, attacking humans is rare.

The most dangerous fish of this group is the Red-bellied Piranha (Pygocentrus nattereri). The Red-bellied Piranhas have the sharpest teeth and the strongest jaws among the species of piranhas. They occupy shallow waters and hunt in groups of more than 100 individuals. Many groups can congregate for feeding when the prey is big enough. 

Two other piranha species that deserve the spotlight are the Pygocentrus nattereri and the P. pirya. They are also dangerous to humans and attacks are not rare. They inhabit waters of the Orinoco and Amazon river basins and São Francisco river, respectively.

Candiru/Toothpick fish

The Candiru is also known as Toothpick fish. This group is composed of more than 280 species. They prove that not all dangerous fish need to be large, they only grow to up to 12 centimetres. These fish inhabit the Amazon river area. Its body is elongated and translucid. They feed on blood and normally are found parasitizing other fish.

One specific species of these fish is a threat to humans because they can swim through the human genitals and cause severe infections, sometimes resulting in surgeries. They open the covered-in-spines operculum and wound the urethra area. This behaviour is a result of the parasitizing feeding habit.

Pirarucu

The Pirarucu is a gigantic fish scientifically known as Arapaima gigas. This fish inhabits the calm waters of the Amazon river basin. It can grow up to 3.5 metres and weigh up to 330 kilograms.

One curiosity about these fish is that they are also known as the bony tongue. Because of their “teeth” on the tongue. They also have two breathing systems, branchia and lungs.

They can be harmful to humans due to their size and weight. Once captured, they can hit the fisherman and even cause death.

Goonch fish

The Goonch fish is a gigantic catfish species, which reaches up to 2 metres in length. It is also known as Giant Devil catfish. This fish species inhabit deep areas in fast flowing rivers of the Indian Subcontinent. 

They have a muddy-brownish colour that favours their camouflage. They are supposedly responsible for several attacks on humans and their disappearance. These multiple events reported humans being pulled under the water and completely disappearing. The witnesses report they were muddy-colored creatures.

Payara/Vampire fish

The Payara fish is also known as Vampire Tetra or Sabre Tooth Tetra. It is also an inhabitant of the Amazon River basin. They can grow on average 1.2 metres and live up to 12 years.

The Payara is a predatory fish species and actively seek prey. They have razor-sharp fangs designed to kill. The Payara’s fangs can reach up to 15 centimetres. 

Many people consider the Piranhas as the most carnivorous killer fish of the Amazon river basin. However, the Payaras are much more dangerous and aggressive. They can even eat up the piranhas. Due to their size and behaviour, they can eat a whole human hand or foot. Although they are aggressive and dangerous, no documented cases of Payara attack on humans is related to death. 

Giant Freshwater Stingray

The Giant Freshwater Stingray can be found in rivers and estuarine areas of Southeast Asia and Borneo. This species can grow up to 2 metres and weigh up to 600 kilograms. 

The Giant Freshwater Stingray is typically not aggressive and preys on small fish and invertebrates, such as molluscs and crustaceans. However, to humans, the threat coming from this animal is its barb on the tail. This barb is covered in toxic mucus and is capable of piercing a bone. Thus, it can cause severe injuries and result in death.

Most of the human accidents with Giant Freshwater Stingrays are associated with fishing activities. They are caught incidentally by gillnets and fish traps. Then, when the fisherman tries to release the stingray, it is common for it to be stung by the barb.

Conclusion 

In this post, we determine a few of the most dangerous freshwater fish. We also outlined their biology and ecology.

If you have any thoughts or doubts, feel free to drop us in a comment below!

Frequently Asked Questions (FAQs): Dangerous freshwater fish

Are there any freshwater fish poisonous?

Yes, many freshwater catfish are venomous. They are spread and very common around the globe. They have stingers distributed on their bodies. However, there are also stingrays. They also have a sting, the barb. And in most of the species, these barbs are covered in toxic mucus. Sometimes this venom can cause a lot of pain, but sometimes it causes some systemic manifestations

What freshwater fish bite humans?

Here are a few of the freshwater fish species that are capable of biting humans, some may even cause death: 

–       Siluro/Wels catfish;

–       Goonch catfish;

–       Giant Freshwater Stingray;

–       Porac/Electric eel;

–       Piranhas, specifically the Red-bellied piranha.

Can a catfish eat a human? 

There is no proof that some attacks on humans and disappearance were caused by catfish. Some of them may hurt due to their stingers or due to their sizes and teeth to defend themselves. Although, there are people that claim some species, such as the Goonch catfish and the Siluro, are responsible for some human injury and disappearance. 

What fish has human-like teeth? 

Sheepshead has “human-like” teeth. They have well-defined incisors and molars to break structures to obtain food, such as shells of oysters, crabs, mussels, and barnacles, and to crush the food before driving it to the stomach.

Do carp fish bite humans?

No, carps do not bite humans. However, they can hit and hurt while struggling out of the water. Their teeth are too dull and their mouths too small to cause damage to the human skin.

Do Piranhas eat humans?

It is very rare, but not impossible at all. Although Piranhas receive the reputation of ferocious predators, it is very uncommon for them to attack humans. During scarcity of food, it is more common that Piranhas attack almost anything that moves in front of them. In addition, the Red-bellied piranha is the most dangerous piranha species. They are known to cause injuries to humans through biting, but these attacks are usually not fatal.

References 

Lucas, A. S. Top 10 peixes mais perigosos do mundo. https://top10mais.org/top-10-peixes-mais-perigosos-do-mundo/

Lurking in Lakes and Rivers: The 10 Most Dangerous Freshwater Fish. 2020. https://insmoothwaters.com/most-dangerous-freshwater-fish/

Scott, B. M. 2007. Top of the Food Chain: Taming the Untamable – Giant Payara!https://www.tfhmagazine.com/articles/freshwater/taming-the-untamablegiant-payara

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