Fish People are a specific category of (usually) intelligent, underwater fantasy species. While they're humanoids (one head, two arms, two legs), they don't look human at all; their bodies, especially the faces, have a fish-like/reptilian appearance. This means that mermaids are not true Fish People, at least not the kind described here. Neither are more human-like sea dwellers such as Aquaman or Namor the Sub-Mariner. A Fish Person's Character Alignment and ability to survive on land vary depending on the character and the series.
While Fish People are most often a pre-existing race, sometimes they are former humans (or fish) who are the result of mutation. This origin seems especially prevalent in Western Animation.
Merfolk can have a similar style, but fail the critical "has legs" check... most of the time. Since many Fish People appear somewhat reptilian, Lizard Folk and Reptiles Are Abhorrent are also related tropes. Expect them to create breathtaking Underwater Cities.
Fish People are a subspecies of Petting Zoo People. Super Trope to Shark Man.
The Fishmen from One Piece. Their sister species are the Merfolk, traditional mermaids. The two species get along pretty well and can even interbreed, but the Fishmen tend to be more aggressive and angry towards humans while the Merfolk are light-hearted and naive. Also Fishmen are 10x stronger than humans from birth and can use water as a weapon.
It was later revealed that Merfolk can use water as a weapon in pretty much the exact same way.
One of the many denizens found in the Magic World of Mahou Sensei Negima! was a dolphin man. A trucker dolphin man. With flippers for hands. How he was able to hold things like the postcard from Makie and Yuuna without fingers, we may never know.
Mazinger Z: The Chip Kamoy ("divine fishes" in Ainu idiom). They showed up in the Gosaku Ota manga, and they were a race of gigantic, bipedal, humanoid maneating fishes from another dimension who raised herds of humans as if they were cattle. Their bodies were scaly and covered with fins. However, they had depleted their homeworld's natural resources and were running out of food, so they crossed over to our dimension to find more prey.
Slayers pokes fun at this trope - the standard fishman in Lina's world is basically a giant fish with stick-thin limbs.
During the Naruto Land of the Sea filler arcs, Amachi's ambition was to create the perfect aquatic soldier, transforming humans into Fish People. Isarabi was a partially successful trial run, but could not fully switch back to human form. Amachi made himself into a perfect hybrid, but ultimately discovered that without any skills other than becoming scaly, he wasn't the ultimate warrior he'd hoped.
Kisame and Fuguki (Samehada's previous owner) both look very much like a shark and a puffer fish, but they're apparently just weird looking humans except when fused with Samehada.
The Big Bad of Blue Submarine No. 6, Dr. Zorndyke, floods the earth in an attempt to wipe out humanity and replace it with his own races of genetically engineered Petting Zoo People, the most numerous of which are the aquatic varieties. Not surprisingly, all of the females are Cute Monster Girl 's, especially the mermaids.
People with fish for heads (yes, that's right, fish for heads) from another planet are shown in act 47, in the fifth arc of the Sailor Moon manga. They can be seen here at about 3:36.
Abe Sapien from the Hellboy comic and its adaptations in other media.
Some of Namor's enemies are Fish People, like Tiger Shark (or whale people in Orca's case) and most of the people from Atlantisalmost count as Fish People. Namor is a mutant, however.
His second wife Marrina was even closer.
Atlanteans in Invincible are a parody of this. Marvel and DC both have Apparently Human Merfolk, or very close to it. Invincible's Atlanteans live like the Atlanteans of Namor and Aquaman - the Theme Park Version of a feudal society, Schizo Tech, frequent problems with Kaiju, and a king who unaccountably spends a lot of time on land as a superhero - but they are definitely Fish People, not apparently human.
Then there's Triton from the Teen Titans animated series, and Aqualad's little Mechanic friend Tramm.
In Swamp Thing, a new generation of vampires are hatched in a town submerged in stagnant water that have the form of fish people (though closer to fish). Charmingly, they eat each other until only one huge newborn remains.
Gungans, including the notorious Jar Jar Binks. Though they're more amphibian people.
In the original trilogy, Mon Calamari like Admiral Ackbar ("It's a TRAP!") and this dancer. It seems odd, but they can squeeze those hands and feet into human-shaped boots and gloves as needed. From the same planet we get the Quarren◊, who are even more squidlike than Kit.
The character was in a bar and appeared to have been drinking to excess. He was hallucinating, but then again, this was The Seventies.
In Pirates of the Caribbean, Davy Jones and his damned crew steadily mutate into these over the decades of service on the Flying Dutchman. Except the disobedient, who become more coral-like, and end up fused with the ship itself.
It's not just the disobedient. The implication is that, by the time your hundred-year contract is up, you will be part of the ship. One of the crew has the next helm growing out of his spine.
This has more to do with Jones's bitterness towards Calypso than the ship itself, however - when Will replaces him as captain, everyone on the ship spontaneously reverts to normal. Will then retains his humanity all the way through to his post-credits reunion with Elizabeth.
Although we never see the title monster in Cthulhu, the protagonist does encounter these creatures in a pitch-dark tunnel beneath Rivermouth.
"There were things, and they were everywhere! They were on the ground, they were on the ceiling, they were everywhere!"
The Last Lovecraft: Relic of Cthulhu has Starspawn and his pets as fish people; they're weakened from being away from the ocean. Also there was a curious "Half-Breed" show, probably offspring of one of the many rapings we hear about in the movie.
Roger Corman gave us Monster, aka Humanoids From The Deep, about a bunch of fish people who want to come ashore and, well, knock up the local gals. Oddly enough, this is something of a running theme in fish people-related horror stories.
The titular character/monster in the Robert W. Chambers story "The Harbor-Master" is one of these; it's thought to have been the basis for...
Michael Reaves and Steve Perry's novel Dome is set at a futuristic undersea research lab. One of its residents volunteers to be genetically modified into a Fish Person in order to better survive the underwater environment.
Barlowe's Guide To Extraterrestrials depicts a Guild Steersman from Dune as resembling this trope.
A microscopic version of this trope appears in "Surface Tension", a short story by James Blish. A colony ship crashes on a planet virtually devoid of land, so they create (via genetic engineering) tiny aquatic humans to carry on their legacy after they've died.
The Scar by China Miéville has several aquatic races, most notably the Grindylow. Also the simply-named Menfish.
The Slayers novels feature this too (obviously, since the anime was based of them). There are apparently several varieties of fish people of varying degrees of icthyism, but Nunsa, the one who appears in the first novel, takes the cake; talking and walking around on land are his only concessions to the "people" part of the trope. When Zolf tells him to kiss Lina to gross her out, he comments that he's considered the most desirable mate in his school (the best catch, you might say), then sits down and waits patiently. When quizzed, he claims he's waiting for the eggs, since he's not sure what kissing is, but is vaguely aware it's related to mating.
Marsh-wiggles from The Chronicles of Narnia. WikiNarnia describes them as having "green-grey straw-like hair, large ears, long legs and arms, webbed hands with long fingers...hard webbed feet, similar to those of ducks...a muddy complexion and greenish skin." Oh, and they're also an entire race ofEeyores—the only one we meet, Puddleglum, is seen as a Wide-Eyed Idealist by his fellow Marsh-wiggles, and he has lines like:
"Those eels will take a mortal long time to cook, and either of you might faint with hunger before they're done. I knew a little girl—but I'd better not tell you that story. It might lower your spirits, and that's a thing I never do."
"The bright side of it is, that if we break our necks getting down the cliff, then we're safe from being drowned in the river."
"And you must always remember there's one good thing about being trapped down here: It'll save funeral expenses."
The new series has the Hath, which are definitely more human-like, and the Saturnynians, fish-like aliens with insectoid exoskeletons.
The Expanded Universe has the Krill and the Selachians, as well as one-time Doctor Who Magazine companion Destrii.
The Buffy the Vampire Slayer episode "Go Fish" had one of these, where the swim team magically mutates into fish dudes due to their coach giving them illegal, Soviet fish-based steroids. We know, it makes no sense. Unusually for monsters in a Buffy episode, they all lived Happily Ever After in the ocean.
It's really not a happy ending for them since they lost their human personalities, so the swim team essentially died.
One legend pertaining to the legendary Merovingian Dynasty claims that they were descendants of Fish People. The writers of the Holy Blood Holy Grail, and The Da Vinci Code decided to interpret this as that they were in fact the descendants of Jesus Christ, since early Christians used a stylized fish as their symbol, not to mention that the Greek word for fish, icthys, formed a nice acronym of Jesus's name and titles. There isn't an ounce more evidence to prove this theory than there is to prove actual Fish People's involvement, though.
This seems to be based on a rather desperate interpretation. "Merovingian" means people of the sea, and so originally most likely referred to a people who lived on the coast, or settlers who came from overseas.
The Merovingians were perfectly historical, and they're called that after an ancestor named Merovech. If The Other Wiki may be believed, his name has, despite the similarity to "mere", German Meer, etc, nothing to do with the sea, but means "famed fight".
There is a report of the 16th century King of Poland being shown a fish-like creature resembling a Bishop, that gestured to be asked for release to a group of Catholic bishops. Upon its release, it made the sign of the cross and disappeared back into the sea.
The umibozu mentioned above probably served as a folkloric antecedent for the ningen, a sort of gigantic (and absolutely terrifying sea creature with vaguely human characteristics. It's probably an urban myth. Hopefully.
Ginny (or Jenny or Jeannie) Greenteeth, who according to British cautionary tales drowns kids who play too close to the water's edge, is usually described as a green-skinned monster.
According to Japanese Mythology, earthquakes are caused by a giant catfish called the namazu. Following the Great Ansei Earthquake that struck Edo (Tokyo) in 1855, a new type of watercolor blockprint, called namazu-e (catfish pictures) became popular. Examples featuring anthropomorphized catfish can be seen here.
The mermaids of Barracora are an unorthodox scaleless hybrid of humans and barracudas.
The Savage Species supplement introduced the anthropomorphic animal template, which can be applied to any creature with the Animal type, including mundane fish.
In 3E, every 1 in 100 sahuagin would be born looking like their hated enemies, the sea elves. Most of the team, these mutated sahuagin, called malenti, were eaten by their own parents. Some of them are raised to be deep cover infiltrators for sahuagin, though.
And then there are the kuo-toa, which are subterranean fishmen.
The Fighting Fantasy gamebook world of Titan features the Fish Men, a race created by an Evilutionary Biologist sorcerer who blended a number of unwilling humans with fish. They tend to be solitary, cruel, and hostile to humans, attacking them with tridents when the humans intrude on their territory or simply to steal the humans' riches.
The Triton parahumans in GURPS: Bio-Tech have their gills on their chests in order to function properly. The extensive modifications needed to let them survive underwater required making them inhuman inside and out.
The Merfolk of Magic: The Gathering are more fishlike than most, featuring scales all over their bodies, and some have legs instead of fish tails. There are also Homarids, who are lobster-people, and Cephalids, octopus-people.
Fifty Fathoms has fish people, crab people, squid people, dolphin people, seal people and (villainous) octopus people.
The Sea Folk, a playable race in Blue Rose, are technically more like Dolphin People — they can't actually breathe underwater (but can hold their breath for an hour or more), aren't scaly, and are portrayed as graceful and elegant rather than repulsive. They can also live on land and interbreed with normal humans, although they need to immerse themselves in water daily and usually stick near the coasts.
Along with the standard D&D sahuagin and locathah, Pathfinder has anglerfish-inspired ceratioidi and shark-like adaros.
The Barraki and Karzahni in BIONICLE are of the mutated former land dwellers kind, save for Ehlek the Eel Barraki, who was aquatic to begin with.
Lagoona Blue from Monster High, who has a pretty strong case of the Innsmouth Look going on- blue skin, protruding eyes, full lips, a nose so flat as to be virtually nonexistent, fins on her arms and legs and serving as her ears, and webbed fingers. There's also her boyfriend, Gillington "Gil" Webber.
The Neptune's Shell from Terraria turns the player into one when they come in contact with water, allowing them to move through it as if it was air.
The Zora from The Legend of Zelda games. Though they're much better looking and friendlier than most fish people in the post-Ocarina of Time console games, the 2D games generally portray them as ugly monster enemies. Queen Oren of A Link Between Worlds is a sort of hybrid between the two designs, sporting the color scheme and secondary features of the 2D Zoras but is friendlier and more humanoid like the 3D Zoras.
Warcraft has the murlocs, primitives who resemble piranhas with arms and legs in place of fins and tail. They're found almost everywhere that has coastline and are generally considered pests by the smarter races due to their typically aggressive nature and high rate of reproduction.
There's also their Pandaria native cousins, the jinyu, who are larger, more humanoid, and much more intelligent, being able to speak the common tongue and integrate themselves into society.
Lakelurks from Fallout: New Vegas are reskins of the aforementioned mirelurk kings, and possess the same stereotypically finned, ichthyoid appearance. They also retain the mirelurk kings' powerful attacks and tendency to cluster in areas near water.
Blue Minions in the Overlord series get very close to this at least.
In Sonic Adventure 2, a tiny version of these appears as one of the animals you can give to your Chao.
Dominions 3 has Icthyids, Merfolk, Tritons, Amber Clan Tritons, Kappa, and several other species that fit into this. The Icthyids and Amber Clan Tritons are the most notable, the first because they live on shorelines and under the sea, making useful troops for water entry; and the second because they are terrifying beings armored in Amber that can and will massacre armies bigger than them.
Dominions 3 also has the nations Atlantis, Oceania, and R'leyh, all of which have fish people, though Atlantis and especially R'leyh have plenty of full blown sea monsters as well.
The Merian race from Lusternia. They are decidedly non-human in appearance, being scaled, hairless, blue and finned, but are a highly attractive, intelligent and noble race with a proud history of scientific accomplishment. Interbreeding with humans has resulted in a few crossbreeds, some even having hair - but however diluted the Merian genealogy, all "real" Merians can breathe underwater.
Soul Reaver has the rahabim, a specialized breed of vampire that not only overcame the usual vampiric weakness to water, but adapted fully to it. While their progenitor, Rahab, is more of a merman with a humanoid vampire upper torso and a shark-like tail instead of legs, his progeny are classic gill men with flipper-like feet, froggy faces and a pair of dorsal fins.
Mona Lisa, from the Teenage Mutant Ninja Turtles (1987) episode "Raphael Meets His Match", was originally a human—specifically, a physics major in college. In short order, she was kidnapped by modern day pirate-cum-genetic engineer Captain Filch, forced to help with his evil experiments, and mutated while escaping from his ship. The result was a fish/reptile Mix-and-Match Critter who was smart and strong enough to help the Turtles stop Filch—and cute enough to become Raphael's Girl of the Week. Her action figure adds to the fishiness by giving her gills.
Ray from the episode "Rebel Without a Fin" is a male example that is more fish-like, being a mutant manta ray, with abilities from other marine animals; in the same episode, April O'Neil is also turned into a mutant fish.
Neptunia from Darkwing Duck is another mutant Fish Person. She starts out as a Well-Intentioned Extremist who wants revenge against the surface world for polluting her ocean home (yes, just like one of the DuckTales examples above), which caused her to mutate from an ordinary fish. However, she does a Heel-Face Turn and eventually joins Darkwing's Super Hero team the Justice Ducks — even though, as she protests any time anybody mentions the name, she's not a duck.
Sealab 2021 gives us half-shark, half-Eric Estrada Sharko. Then there's Dolphin Boy, who looks perfectly human but speaks dolphin.
On Futurama we have the lobster-esque Decapodians (Zoidberg's race), as well as the residents of a submerged 31st Century Atlanta, who evolved into Mermaids as a result of the Coca-Cola factory causing massive amounts of caffeine to end up in the water.
In the Adventure Time episode "Susan Strong," after finding what he believed to be the last tribe of true human beings in the Land of Ooo, Finn discovered that they were merely fish people with hats, possibly save for Susan herself.