1. The Dragonfish
The Dragonfish is a fearsome predatory fish notable for its long jaws filled with teeth, aggressive nature, and large size. They are no relation to actual dragons, have no breath weapon, or anything else. The dragonfish is a large creature, with the average adult being six to eight feet long and up to 300 lbs. They are voracious and territorial fish, not unwilling to attack anything in the water with them. They will take swimmers, children, or even gut horses and livestock fording narrows in a river.
Dragonfish most likely garnered their name through their teeth being traded as 'dragon's teeth' given their large size and fearsome appearance. Also known as the Tiger fish.
2. The Leith'jess or Fangfish
The fang fish is an ancient predator lurking in the rivers. It has a pair of pronounced fangs in its bottom jaw that it uses to grab and drag things underwater to drown and then consume. It long ago adapted to hunt the edges of the water, snatching creatures basking on the surface, drinking from the edge, or even flying too low over the water. While having a horrendous bite that can cause fatal injury, most victims of the fangfish drown before they have a chance to bleed out. The average fangfish is three to four feet long, and most often a threat to children, small and medium livestock, and the unwary fisherman. They have indiscriminate growth, so ancient fangfish can grow up to ten to fifteen feet and are large enough to take grown men, and even large livestock.
The fangs of a fangfish are prized for their size and sharpness.
3. Great Muskellunge or Great Muskie
The regular muskie is an aggressive fish, growing up to seven feet long and menacing anything smaller than it is. They are long and slender, fast and powerful strikers. The Great Muskie can reach up to thirty feet and become a true river terror. These fish can be mistaken for tree trunks floating in the river and when roused, they can sink canoes and damage small river ships. They can sever limbs with a bite, and for most people, a single bite is a fatal encounter.
Rivers with great muskies tend to have fishing traditions built around landing the fish and even attempts to cull the beasts when they are young and smaller. If left unchecked, great muskie can wipe out a fishing village by taking not just the fisherman's catch, but the fisherman himself too.
4. Elder Chucklehead or Great Polliwog
Catfish is such a modern term, but the Elder Chucklehead is just that, a massive catfish that can reach up to a ton in mass and have a maw large enough to devour small and medium creatures with ease. While not predatory, the chucklehead isn't above a bit of ambush work to get a meal. Anything too large to swallow is taken and stuffed somewhere under rot has advanced enough that the meal can be taken apart and swallowed in pieces. Given the warm waters and cold metabolism of the chucklehead, it can easily hold a large creature its caught or found in its mouth, chewing, for days, until it starts falling apart.
Chuckleheads are either considered a good source of food, or untouchable. In the latter case, they are in an area where the fish are known for eating humans, alive or otherwise. We dont eat that which eats us.
5. River Dragon Fish
Like the Dragonfish, the River Dragon Fish is a large predator with a jaw full of horrendous teeth and an appetite to match. Unlike the dragonfish, the river dragon fish is a slow-natured ambush predator. It floats easily, masquerading as a piece of debris until something catches its interest, and then it goes from a log to thrashing fury, teeth, and blood in the water. They most often prey upon river herbivores like manatees, hippos, and anything large and ponderous crossing the water. Some acquire a taste for humanoid species and have learned to stalk boats and nets.
Note - Arapaima
6. Tanar'ian Chucklehead
The Tanari'an Chucklehead can grow up to twelve feet long and half a ton in weight, with the outstanding features of having bone-like armor across its head and dorsal areas. Is this a dangerous and aggressive fish? Absolutely. Originally coming from one of the unknown hells, where its ancestors grew large and dangerous enough to stun and devour lesser imps, devils, and demons, the terrestrial Tanar'ian chucklehead can use magic like abilities to stun or cause fear paralysis in their intended prey, typically by splashing out of the water and flashing their unnatural colored fins and belly. A stunned foe cannot move and is easy prey for the fish to drag underwater and consume at its leisure. Tanar'ian chuckleheads demonstrate both modest magical resistance and damage reduction, making them difficult to seriously injure, let alone kill.
7. River Cloaker
Stingrays aren't really a thing in fantasy, but the Cloaker beast is. The River Cloaker is a stingray that looks like .... a ... cloak. It is large to very large, and typically feeds on river bottom dwellers, carrion, and whatever it can find. They are not predators, unless you are a shellfish or crustacean. What makes the River Cloaker a danger, is that when it is threatened, it has a dorsal spine the size of a knight's lance and it terrifyingly accurate with it. A foe or harasser struck with the spine takes damage as if being hit with a cavalry charge. This can kill most offenders, or critically maim anything to the point that rather than pursue the cloaker it will retreat to deal with the horrible bleeding wound in some meaty part of its body. If the harasser is suitably wounded and weak, it isn't unknown for the cloaker to wrap up its foe and swim somewhere quiet to slowly eat them.
8. Thunder Fish
Also known as the electric eel, in the fantasy world, the thunder fish can cast thunder or thunderbolt, causing significant injury to a target. This isn't done to feed, but rather to prevent predation. Thunder fish are more likely to blast a more aggressive fish, or fisherman, and then slip off to go to their normal business of skulking for small crabs, insects, and such. A hunting thunder fish might blast a watery shallow to stun or kill the small creatures in it to gobble them all up and swim away.
9. Goblin Fish
The modern person would call these piranhas. Goblin fish are greenish gold piranha.
The Torchal is a creature more associated with the ocean, cutting through the water with long lines and sharp fines, its dorsal fin a knife through the water. Torchals are freshwater sharks, large and aggressive, and drawn to blood. Why they venture so far upriver is unknown, but they do, and they are terrors. Often when there is a torchal in the river, a fishing community is better off leaving the boats tied off and subsisting off of their dried and preserved goods until the torchal moves along to different hunting grounds.
Torchal especially like the taste of human and demi-human blood. They ignore goblins completely.
Note - bull sharks can enter fresh water and travel hundreds of miles upriver following prey.
11. Serpent Fish
The Serpent Fish is technically a fish, but it has the shape and proportion of a snake. They can grow up to thirty to fifty feet long, and more horrifically, can survive on dry land for three to five days. So long as they can keep themselves passably hydrated, even longer. Being a marine creature, few land animals are aware of their scent, or how to avoid them. They will stalk rivers, cross dams, infest ponds, and in one horrific instance, roost in a cistern. They have no special abilities other than being strong, tough, aggressive, and patient enough to cause nightmares.
Presented without embellishment, the arapaima is a South American fish that can grow up to fifteen feet in length and are strong enough to grab a person by the leg and drag them to their death underwater. Jeremy Wade has an extensive practice in catching these frightening fish, which are only surpassed by the African Tigerfish aka entry #1, the Dragonfish.
13. Stormy Chucklehead
The Stormy Chucklehead is an electric catfish and rather than having the innate ability to cast thunder or thunderbolt, the Storm Chucklehead can produce Shocking Grasp when it bites something, sending an electric current through anything in its mouth. It is a predator and will use its electric bite to semi-cook its prey so that it is easier to consume. They are smaller than other chuckleheads but are still large enough and dangerous enough to harry fishermen, both on boats and onshore.
14. Werewolf Fish
The werewolf fish is a solitary predatory with a blunt hammer-like face and a jaw full of jagged mismatched teeth. While large enough to menace small and medium-sized creatures, they are generally not a threat to anything larger. Most of the time.
When the full moon rises, the werewolf fish can double or triple in size, grow armor like scales, and its teeth can become astonishingly sharp. During the nights of the full moon, werewolf fish hunt aggressively, devouring as much as they can, even teaming up to kill even huge or giant-sized creatures and devour them. Once the moon wanes, they reduce to normal size and then will lay their eggs. The waning moon tends to signal the spawning season. This doesn't mean they lay eggs once a lunar month, but rather, the different broods in different areas will be spawning under the moon. Which moon varies from region to region, and most locals know in which full moon to avoid swimming.
15. Crossbow Fish
The Crossbow Fish is a seemingly normal-appearing, albeit large, river fish. The real-life archer fish can spit a glob of water with enough force to knock insects out of the air, or off of grassy perches near the water. The crossbow fish is a good deal larger, several feet long and several dozen pounds in weight. It can spit a glob of water with enough force to daze a small-sized creature. The danger of the crossbow fish is that it will work with other fish. A crossbow fish might snipe a person off of a boat, so once they are in the water, a larger predatory fish can kill them, and the crossbow fish will scavenge from the kill.
Here end the monstrous fish inspired by real world creatures.
16. The Prismatic Fish
Also known as a seven scaled fish, this fish is rare in the extreme. When caught, it can defend itself with Prismatic Spray but as a splash/area of effect rather than a ray or cone. Should a fisherman survive this magical assault and retain control of the fish, it will grant them one Wish. Being a fish, it is not bright, and the wish will be granted in the most direct manner possible.
The real danger of the prismatic fish is that wishes for immortality will turn the fisherman into another prismatic fish. They become intelligence 1 and become a magical immortal fish.
17. River Jelly
Like a gelatinous cube, the river jelly is 'organized acidic water' that moves along the bottom and devours any organic material it encounters. They are almost invisible underwater and most swimmers or divers might be halfway inside one before realizing the red in the water is their own blood as the river jelly is dissolving their skin. The river jelly likes slow-moving water, and if they congregate in numbers they can cause a river to start flooding by simply blocking the flow of water.
A river can be depleted by river jellies. Once all the organic material is gone, the jellies will start feeding on each other, or they will develop cyst-like shells and become dormant nodules in the bottom of lakes. This is common when their actions also cause oxygen depletion in the water. Some river jellies will become aggressive and hostile, often turning pitch black and having a viscosity like tar. (The Lake Blob from Creepshow 2: The Raft is a black river jelly)
18. Marsh Stalker
The Marsh Stalker is a primitive fish, much like the coelacanth. It is roughly the weight of a horse and has the ability to crawl out of the water on its short, thick, forefins. So long as they can stay moist, they can stay out of the water almost indefinitely. In the water they are typical slow-moving ambush hunters, smashing their primitive armored heads into prey to stun it before dragging it back into the water to tear apart with the sharp bony mouth plates. On land they are decoy predators, pretending to either be dead and pouncing on scavengers, or as ambush predators, attacking legs, feet, and bellies. Marsh stalkers can become problematic in spawning season, and large numbers of them can migrate into marshy shallows to fight, breed, and a short time later, lay their eggs and vanish.
19. River Kitten
River Kittens are somewhere between amphibians, fish, and cats. They have legs and can move around on land easily enough. This cuteness makes them popular among people who live along rivers, much like keeping pet otters or beavers but with more scales and less fur. The problem with the river kitten is the same problem most people have with kittens, they become cats. A full-grown river kitten, depending on the sub-species, can be as small as a bobcat, or as large as a tiger. These greater river cats are a threat to livestock, children, and anything that catches their attention.
River cats are closer to amphibians than mammals or fish. They are cold-blooded, lay eggs, and can hibernate in bad climates. They are also aggressive, intelligent, curious and like large cats can either be semi-tamed or become terrors. For a point of reference, Ghost and the Darkness (1996) was a movie that detailed the reign of terror inflicted by two lions against a human settlement.
20. River Wisp
The River Wisp is used as a warning to keep children from wandering off on river adventures by themselves and to stay out of certain areas for being dangerous. Unfortunately, it is a real creature. Like the oceanic anglerfish, the River Wisp is a large almost trap-jawed fish that lurks just under the surface while extending a decoy appendage above the water. The fish can use Lesser Illusion and Audible Glamour from its lure, allowing it to project visual and audible traps to draw victims to it. The older the river wisp, the more complex the illusions it can create, with ancient ones being able to craft a specific victim with fragmented lines. The animal is of limited intelligence and it's illusions speak with the intelligence of a parrot, repeating what it's heard. Lots of weeping and crying for help, a good deal of screaming and panic. And blood. Lots of blood.
Many ghosts that are repeatedly seen in watery areas are really just old, established River Wisps hunting.
21. Dread Spawn of the Depths
The dread spawn of the swamp is a horrific combination of armored snail, kraken, and crocodile. The creatures have a spiral shell that can grow as large as a dozen feet wide, and the beast dwelling inside has tentacles, a fanged beak, and a reach like a constrictor snake. It's an ammonite, large and aggressive enough to eat medium-sized prey easily, and large prey can be ambushed and harmed enough to be stalked or ignored until itit'seak enough to overwhelm with entangling tentacles and a crushing bite. They are found in lakes and deep water, so waders and swamp folk have no need to fear this monster.
The Squirmhead is a large lungfish. They can grow up to twenty feet long and are decent ambush predators. The end of their snout/head is a mass of worm-like tendrils that they use to taste the water or air, and chase their prey by scent. These long barrel thick serpentine horrors leave the water to slither around and hunt less mobile and less aware prey. Typically this includes bird nests, carrion, and slow-moving land animals that don't have a counter for being swallowed whole. In river settlements, this includes pets, tied-off livestock, and people who are sleeping in an area where the Squirmhead can get in quietly. Fighting them can be difficult as they have a strong tail lash, and their skin is dense and rubbery.
A common folk story about Squirmheads is that they like to eat dirty little boys and girls who don't wash properly, and if you don't clean behind your ears and between your toes, the squirms will crawl out of the bog and eat you right up.
23. Freshwater Aboleth
Typically found in caves and in exotic alien locations, freshwater aboleth and more common and less dangerous than their eldritch cousins. Most reach no more than four meters in length and a ton in weight. They retain the physiology of tentacles, and a lamprey-like mouth, but thankfully, their psionic abilities are much lessened. It is speculated that since they feed on far fewer adventurers, heroes, explorers, and magic users, this has weakened their power. Most subsist on a diet similar to any other freshwater predator, fish, marine birds, and whatever they can catch.
Freshwater Aboleths lack the ancestral memory of their MM cousins, though those that do manage to eat a few magic users or psionicists can see their powers develop. There are two factors keeping the freshwater aboleths from reaching their potential, a reduced amount of highly intelligent prey to feed, and an increased number of near mindless predators that compete for food and sometimes eat freshwater aboleths as well.
24. Crocodiles and Alligators
Not much to dress up here, a large, potentially aggressive, ambush hunter reptile. Plenty of trouble for anyone who runs afoul of them.
25. Emperor Leech
Emperor Leeches are almost a foot long, writhing, and horrific. These parasitic bloodsuckers have evolved in an environment where megafauna are common and can survive a foot-long leech feeding on them. A medium-sized creature, like a human, can survive a single leech feeding from them but will suffer from exhaustion and be at highly increased risk of infection or even permanent stat loss. More than one, and the victim will likely perish. People who live in the rank and stagnant waters are aware of the risk emperor leeches present for children, the elderly, the weak, and those who cannot defend themselves.
26. River Leviathan
Large enough to destroy canoes and kayaks, and strong enough to damage small river craft, river leviathans are enormous beasts that seem to drift through the riverine shallows. They are tank-like in build, with a thick body, short stumpy legs, and an enormous head with impressively large tusks. They are aggressive and can deliver a deadly organ puncturing bite with ease. For the most part, if the leviathans are avoided, they are generally not a threat. In the breeding season, they become hostile and very aggressive, to the point that the female leviathans and their young will leave the rivers and lakes to graze on dry land until the boys work themselves out.
The Hellbender is a salamander. The amphibian kind, not the fire elemental kind. It is also the size of a large dog and is generally a pretty peaceable creature, content to consume insects, shellfish, and whatever else it can nip out of the water. If threatened, they can rapidly change colors in an attempt to scare off the predator or intruder. If this doesn't work, they can unleash a barrage of spell-like abilities. They are adept at causing fear, delivering electric shocks, changing their size dramatically, and other abilities. How they progress is unknown, and no two hellbenders have the same spell-like abilities. The only correlation that exists is that the larger the hellbender, the more it can do.
There was a particularly unpleasant hellbender that nested near a now lost subsistence fishing village. It's spell of choice was a deformed version of a summoning spell that summoned, of all things, humans. Or humans as the hellbender was aware of them.
Sometimes there are things seen in the rivers and estuaries, things that cannot be explained. Shimmering lights, dancing fire, green and verdant forests undulating above the waters, a swirling tower of storms, a great giggling of naked women, ships breaking apart and being pulled down by titanic monsters, all this in shallow waters wading distance from the shore. This is the work of the Sirene, or sea cows. These large creatures seem like a strange mix of barnyard pig and seal, great bloated beasts that float gracefully in the water. They are manatees. And they defend themselves, their pods, and their lagoon pastures, with a frightening level of competency in illusionary magics.
The Golfinho is not just a river dolphin, it is a sentient magic using sadist. Appearing as iridescent members of their species, the golfinho has the ability to use spells like charm person, hold person, charm monster, hold monster, suggestion, and the like. Female golfinhos will use their powers to coerce fishermen into surrendering their catches or even giving them tribute at the point of danger. Male golfinhos have a nasty reputation of coercing women into the water to mate with them. A pod of golfinhos can enslave a fishing community, or turn a river ship into a mutiny and bloodbath with everything going over the side and the ship being burned.
30. Freshwater Plesiosaur
The freshwater Plesiosaur, best represented by the Lake Champlain Monster (Champy) and the Loch Ness Monster (Nessie) is a long-necked fish-eating riverine reptile. It is remarkable for its ability to completely disappear, using spell abilities like Pass Without Trace, Greater Invisibility, and Incorporeal Form. They are seemingly aware of gossip and news in fishing villages and river traffic and enjoy the stories that come from their rare sightings. To keep things interesting, the freshwater plesiosaur will let itself be seen, but only by children, drunks, and in the rarest of instances, rescuing a lone imperiled traveler, and using their magic to help them. There are stories of such all but legendary creatures healing what couldn't be healed, granting wishes, and even tossing a few magic swords to would be heroes.
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