10 Monstrous Freshwater Fish Species

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Sharks are rightly respected as premier oceanic predators that can, in the case of the most notorious species, kill humans. Yet a range of truly terrifying freshwater fish haunt the lakes, rivers, and inland swamps of the Earth, not only in the tropics, but even in temperate zones.

In this account, we learn about the worst species to meet while swimming in a lake or river, including the terrifying Wels catfish of European fact and folklore, a possibly deadly six-foot African beast of a fish called the Goliath Tigerfish and learn why running into a Freshwater Stingray may be a lot scarier than meeting a stingray in the ocean.

10. Wels Catfish

A freshwater monster of both reality and legend, the Wels Catfish has a reputation spanning from Germany to Russia, from Italy to Spain, and in the British Isles, where it was dubiously introduced as an aquatic beast to be feared. Unusually for a dangerous fish of this caliber, this hideous and potentially deadly inhabitant of freshwater is a species of temperate environs, worthy of medieval horror films. Wels catfish lurk on river bottoms and work their way slowly through their aquatic habitat, striking when the moment is right to take prey ranging from waterbirds and mammals to other fish, amphibians and possibly… more.

Reaching up to 9.8 feet in length, with descriptions of historic specimens of greater sizes, Wels Catfish have banned from importation by the Ontario, Canada provincial government, while Ontario’s 25 Invasive Species Awareness Program describes them as a fish that poses a threat of attacks on humans in the water on rare occasions. The Wels Catfish has been accused of being an actual maneater, a possibility that is worth considering given their apparent ability to continue growing to huge sizes, especially when fishing pressures are reduced.

9. Goliath Tigerfish

A visitor to Africa might be wisely cautious of at risk but potentially aggressive species like lions or crocodiles. But a danger lurks in certain freshwater environments from a dangerous and beastly hunting fish. Measuring nearly 5 feet in length and equipped with deadly, cone shaped daggers for teeth, Goliath Tigerfish are aggressive, enormous characins, a taxonomical category that places them in relation to both piranhas of popular legend and the tiny neon tetras of the aquarium trade.

Silvery below with stripes that lend both their name and a startling appearance, Goliath Tigerfish are native to the fast running waters of the African Congo. Goliath Tigerfish are highly sought after gamefish, but the tables may be turned. Traveling in packs, these river-going meat-eaters are suspected in human attacks and even fatalities. Native legends tie this species to demonic attacks on humans, a concept that is certainly not without a fair basis. With 32 disproportionately sized teeth worthy of a wolf or shark set in vice-like but fast moving jaws, a single tigerfish can tear a 60 pound catfish asunder with a well-placed attack. A bite to humans would be so devastating that waivers may be required to fish for this species.

8. Freshwater Stingray

If you are in a tropical waterway and you see no fish swimming around but the entire riverbed beneath you starts moving, a bather would be wise to get out of the way quickly or get stabbed and stung. The most humongous freshwater fish you could possibly encounter might be flat. Too enormous to readily fully imagine, the Freshwater Stingray species Himantura polylepis is a relatively recently discovered monster fish that may measure over 14 feet in length and reach more than 7.5 feet in diameter.

The giant inhabitant of Southeast Asian estuaries and rivers dwarfs ocean stingrays and has been considered a candidate for the title of largest freshwater fish on Earth. Brownish in color and bloblike, the fish are a force of nature and should not be disturbed. Weighing around 700 to 800 pounds, the fish feed on a variety of prey items but may pose a sizable danger to any trespasser walking upon them. The stinger is immense and powerful, capable of penetrating bone like a gunshot wound and delivering highly toxin venom. In fact, the length of the stinger sets this fish out as having the longest stinger barb of any ray. Potentially deadly to humans, the venomous ray fortunately only strikes in self defense, though stepping on an animal presents a very real concern.  

7. Muskellunge

Little known is the fact that certain Canadian and American lakes host what is reasonably seen as a freshwater counterpart to a barracuda. A scarce inhabitant of cold North American waters, the Muskellunge or “Muskie” is a real-life lake monster with a potential length of around 6 feet and a possible weight of nearly 70 pounds in the cases of the largest specimens. Resembling a primitive freshwater barracuda in both appearance and behavior, the Muskie the largest pike species on the planet and a fish that is armed to the… well, teeth (literally) with both dog-like fangs to seize its prey and the brute strength to pull down both warm-blooded and cold-blooded food items while they are alive and struggling.

Not only waterbirds and amphibians may be eaten by this predator with sharp and noticeably large teeth, humans may be seized in apparent attacks of misidentification or curiosity, as in the case of one Manitoba fisherman who was left with nasty foot wounds. The large teeth possessed by the Muskellunge and powerful grip exerted by the jaws make this a fish to be respected. Fishermen must exercise great caution in hooking and releasing one of these predators or risk injuries to the hands.

6. Goonch Catfish

In tropical waters, it is not sufficient to fear only shark attacks, either in marine or freshwater environments. Catfish might be thought of as lazy scavengers, but their predatory habits and possible threat to humans may prove eerily shark-like. Simply awful to look at and enormous in its might, predator habits, and size, the goonch catfish of South Asia may weigh in at over 200 pounds and exceed 6 feet in length. Unlike more “soft mouthed” catfish, goonch are a species in possession of sharp, elongated teeth amongst strong, rubbery jaws from which huge barbels extend. The goonch has become the subject of apparently deserved fear in the wake of mysterious human disappearances in South Asia.

Victims in different village-side river sections simply disappeared, dragged down while swimming by a forceful “beast.” The fatal incidents became known as the “Kali River Goonch Attacks” and happened in three different villages located beside the banks of the Kali River in India and Nepal. Following the incidents, enormous specimens were captured by expert angler and River Monsters show host Jeremy Wade (see the video above) in nearby locations. It is thought that the enormous predatory catfish became accustomed to the luxury of human flesh in their diet due to ritual corpse disposal in the river, leading them to drag down live victims.

5. Alligator Gar

When a fish is two-thirds of the maximum size of an alligator and closely resembles the giant reptile, it might be time to exercise more than a little caution in dealing with the species. Considered a “living fossil,” the Alligator Gar is an awesomely primitive fish with a name to suit its appearance, native to the Southern United States, especially the Mississippi drainage basin and parts of Mexico with some Caribbean occurrences. Recorded at lengths of more than 8 feet with a weight record of 327 pounds, the Alligator Gar can even reach 10 feet in length with a weight of around 350 pounds according to anecdotal literature.

Exceptionally successful at mimicking the form of an alligator, this largest of gar species is scaly and robust with powerful, tooth studded jaws that make short work of a wide variety of prey species. Fish, mammals, and reptiles may be taken by this fish, which is unique among gars in having double rows of upper jaw teeth to aid in piercing and holding prey. While attacks on humans are not proven, the results could be catastrophic should a large alligator gar seize a human, and it is worth considering that certain alleged alligator or crocodile attacks could include bites from this ambush predator.

4. Electric Eel

Being bitten, eaten, or stung are not the only risks faced by those who venture into freshwater. Being shocked electrically is an additional threat, if you run into an aggressive or defensive electric fish. Not actually an Eel, but a type of knifefish, the so-called Electric Eel is a denizen of waterways extending widely across the Northern part of the South American continent. Ugly, almost snake shaped and bearing opaque looking eyes and pouting lips, the Electric Eel is the “black sheep” among the different families of knifefish. Breathing air at the surface as a life requirement and equipped with peculiar cellular and organ systems that function like a battery, the Electric Eel is capable of discharging a shock with 860 volts of electricity at one amp for a fraction of a second.  

The giant, wired up fish may reach over 8 feet in length and weigh up to 44 pounds. Not only is the shock powerful, but it can deliver lasting effects – at a respectable distance. While death by Electric Eel encounter is exceptionally unlikely, a very painful and numbing shock can occur if a bather or river goer is shocked, and it is worth noting that one need not be standing on the fish to get shocked – an Electric Eel discharge can persist through a whopping 28 feet of water. Weak discharges are used to find prey, confuse prey items and encourage them to stay put. Then, an exceedingly powerful discharge serves to stun prey for easy consumption. Targets may range from other fish all the way to warm blooded fare including rodents.

3. Arapaima

Scaly, ugly and more than a little snake-like in appearance and demeanor, the reptilian looking Arapaima of the Amazon basin and Essequibo basin, South America is a predator of other fish and sometimes birds. Seizing prey both underwater and from the surface, the Arapaima is an inhabitant of river waters and adjacent swamps and forested backwaters. Distinguished by its size and monstrous looks, this aquatic beast may measure over 9 feet in length, with a potential weight of 440 pounds in the case of the largest specimens. While apparently non-aggressive to humans, two human deaths were alleged to be the result of attacks by this species in Malaysia.

An obligatory air breather that evolved in oxygen-poor environments, the Arapaima is one of those fish species that requires access to the surface to breath through the labyrinth organ. The huge fish’s breathing produces a peculiar sniffling and coughing noise that may alert observers to their presence. While hunting, the Arapaima uses its sharp teeth to rip prey apart, together with its notably bony, course tongue. In contrast to its chomping lifestyle, the mouth is used for a gentle purpose by males, who are mouthbrooders. Interestingly, the female takes on the role of guarding the male in the breeding season, while he carries on his duty.

2. Payara

Resembling a vampire in piscine form, the Payara (alternatively named the Vampire Fish) is a distant relative of the Piranha from the waters of the Amazon Basin with extraordinary elongated fangs originating in the lower jaw. Sleek, silvery in color and skilled as a predator, this agile species has a remarkable set of dentition that is certain to shock the first time viewer. Measuring over 2 inches in length, the huge teeth actually fit inside cavities in the upper mandible that exactly match the shape and position of the teeth.

As a result, the fish can close its mouth fully and look totally normal, resembling a salmon, until it snaps open its jaws and reveals the dagger-like hunting tools. Reaching an average body length of one foot, sometimes 1.5 feet, the Payara is a specially adapted hunter that uses these fearsome fangs to puncture the swim bladder of other fish. Once destabilized through loss of access to the function of this buoyancy organ, the prey can be swiftly dispatched by these creepy yet remarkably specific predators. A Payara bite would easily go right through your hand, so handling with great care is recommended should you choose to either keep Payara in a large aquarium or fish for this species.

1. Piranha

No list addressing freshwater fish to fear would be complete without mention of the most infamous inhabitants of inland waters: Piranhas. While the dangers posed by schools of hungry Piranha have been exaggerated, the fish are still very much carnivorous pack hunters with an unusual combination of both razor sharp, nearly bulletproof dentition formed to a point and a bite force that makes a bench presser look weak. Interestingly, Piranha evolution has favored a powerful bite force over speed of bite. Bulky looking, piranhas look stubby in appearance, concealing their vicious looking teeth behind thick lips. Only when they attack does the innocent looking mouth reveal what looks like a tiny Great White Shark’s dentition. Attacks by Piranhas are rare and far less of a problem than reported and widely believed. However, the threat is real, particularly when food supplies are short.

Research sample findings have included the discovery of severed digits in the stomachs of piranhas and documented cases of loss of body parts from encounters with the fish. Furthermore, victims including drunk and child targets have suffered fatal injuries as a result of Piranha bites. However, the fish have a truly incredible combination of exceedingly powerful jaws and triangle shaped teeth that can make short work of aquatic victims. While notorious, Piranhas represent a mystery beyond the well known Red-bellied Piranha, which can reach 20 inches and a weight of more than 8.5 pounds, and the Black Piranha. The number of Piranha species that exist is a subject of debate, with new species and genetic relationships remaining to be found.  

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