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Like the mermaids and mermen of folklore, their upper half is that of a human while the lower half is that of a fish or other undersea creature. While the males, referred to as mermen, keep their tails intact their whole lives, the females', referred to as mermaids, tails split when they turn 30, allowing them to walk on land more easily. Like the fish-men, they are based on the different fish of the sea; for example, Kokoro is an ice fish mermaid and Hyouzou of the New Fish-Man Pirates is a poisonous blue-ringed octopus merman. Two mermaids of a similar species can also have very different looks; such as Mero and Shirahoshi, who are both smelt-whiting Mermaids.
It appears the mermen can retain more fish-features in the upper body than the mermaids, as shown by the royal princes or the two Ryugu Palace Ministers of the Right and Left. For example, the Minister of the Right has ridges from the top of his head down to his back resembling a seahorse's, his mouth however protrudes outward like a seahorse's mouth. It is also possible for merfolk to have webbing between their fingers like fish-men, as seen with Den.
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They are capable of breeding with humans, as Kokoro was known to have had a human husband and bore a son with him. However, as seen with her granddaughter, Chimney, just one generation after the initial interbreeding, continuing to breed with humans may result in almost all merfolk features being lost. Despite losing the merfolk features, they retain their ability to swim well. Charlotte Praline, a half-mermaid, has shown she maintains all the mermaid features of her father. According to the "biological species concept," the fact that they can all interbreed means that merfolk, fish-men, and humans all belong to a single species. They also share the same blood types. Unlike fish-men, merfolk do not eat meat or fish of any kind, aside from shellfish, so they remain primarily vegetarian. However, it is unknown whether this is a biological or cultural practice.
Pappag explained that merfolk (mermen and mermaids) can have children with fish-men (fish-men and fish-women). However, the child's race is up to chance between fish-men and merfolk. It is possible that there may be some hybridization, and grey area between the two races despite the clean separation indicated by Pappag's explanation. There are many merfolk who bear physical traits normally unique to fish-men, like Den's webbed hands and Shyarly's fangs. Furthermore, fish-men can sometimes demonstrate powers usually unique to merfolk, such as Jinbe's ability to communicate with whale sharks.
Even with merfolk and fish-men being very similar morphologically, the primary form (merfolk or fish-man), subspecies (type of fish), and appearances may differ drastically even among close relatives. The reason is that they still carry the genes of their ancestors in great detail, so their appearance is determined not only by the parents' appearances, but those of all of their ancestors.
Mermaids split their tail when they turn thirty, as shown by Kokoro, Otohime, and an unknown mermaid Luffy saw while riding on a fish taxi. It is also possible for mermaids to consciously merge their split tails back into one while swimming. When Kokoro was swimming underwater to save the Straw Hats, Chimney, and Gonbe, her split tail merged back into one. However, this does not apply to their male counterparts; their tails will not split even after the age of thirty. Oddly, in the anime, several members of the Neptune Army were shown with tails and they always appear bipedal.
So far, all known merfolk subspecies have been based on real aquatic animals, not any of Oda's made-up species.
Merfolk and Their Species
- Kokoro: Icefish
- Camie: Kissing gourami
- Medaka Mermaid Quintuplets: Japanese rice fish (Medaka)
- Ishilly: Striped beakfish
- Kairen: Righteye flounder
- Hiramera: Olive flounder
- Seira: Bluestriped angelfish
- Mero, Shirahoshi: Smelt-whiting
- Fukaboshi: Shark
- Ryuboshi: Oarfish
- Manboshi: Opah
- Hyouzou: Blue-ringed octopus
- Shyarly: Shortfin mako shark
- Neptune: Coelacanth
- Minister of the Right: Sea horse
- Minister of the Left: Catfish
- Den: Bering wolffish
- Otohime: Goldfish
- Aladine: Goatsbeard brotula
Hybrids and Their Species
- Chimney (1/4 mermaid and 3/4 human): Icefish
- Charlotte Praline (Half-mermaid, half-human): Hammerhead shark
- Charlotte Prim' (Half-mermaid, half-human): Octopus
Unlike the fish-men, the merfolk are peaceful, and prefer their race to remain a secret. They often are rumored to aid drowning sailors, plucking them from the sea and taking them to safety. However, some can be violent and hateful, such as the individuals who joined the New Fish-Man Pirates, who look down on humans.
Mermaids are friends to the fish of the sea, fun loving, and usually get along with most people, including fish-men (even though some fish-men can often take advantage of the merfolk's good nature).
Like fish-men, merfolk face dramatic discrimination in certain areas due to past history between them and humans. While the World Government has attempted to bridge the gap, with Jinbe's appointment into the Seven Warlords of the Sea being an attempt to strengthen the bonds between the races (but due to his resignation, that ended in failure), they are still considered valuable in areas where slavery is still legal in this world. A captured female mermaid under 30 (when their tail splits and they can walk on land) that is sold through auction in the Sabaody Archipelago can go for a starting price of 70,000,000. Parted females (those over 30 years old) are worth 10,000,000, and males are worth 1,000,000. Saint Charlos of the World Nobles spent as much as 500,000,000 for Camie, who is younger than 30. The wealthy who buy them usually keep them as a trophy.
When three of the mermaids disappeared in Mermaid Cove, the Straw Hats quickly became suspects even though the mermaids who personally met them say that they are nice people. Though the guards were not quick to jump to conclusions, the conversation with the citizens present echoed the amount of mistrust in humans, especially pirates, and their greediness when faced with the selling prices of mermaids. Caribou quoted a Mermaid being sold for 10,000,000 and called the Fish-Man Island a "treasure trove", showing his lack of respect towards the race.
Because of their huge biological differences, they fail to understand completely the human view of family and habit of categorizing individuals. Humans also fail to understand the fish-men and merman differences.
After the death of Queen Otohime, Prince Fukaboshi told his people the time to repair the damage was too soon for the people to cope with. However, he noted that time will heal the pain they have experienced and that one day they will be able to do what she set about to do and destroy the circle of hate between them and the humans. He told all the people of Fish-Man Island to dream of the sun. To the horror of the island years later, while they had been working towards this goal, the Fish-Man District had been breeding the very opinion they were trying to overcome.
Merfolk are one of the races known to inhabit Totto Land, where they live in harmony with other races.
While merfolk seem to vary as much as humans do, many of the male merfolks carry tridents, and Hyouzou's strength was acknowledged by Luffy, as well as Kokoro being shown to use her tail-fin as a whip-like kick. Merfolk are the fastest swimmers in sea, as demonstrated by Camie, surpassing even the flying fish and fish-men. The mermaids have the ability to talk to fish and call out to them with a sound wave, which is apparently only audible to them. Jinbe, despite being a fish-man, also appears to have a similar ability, leading Crocodile to note the uniqueness. Communing with whales is rarer than with regular fishes, as Neptune demonstrated. Despite this, however and for reasons as of yet unknown, mermaids are unable to talk with Sea Kings with the exception of an ancient mermaid princess of legend and the current princess Shirahoshi.
The fish-men race have many powerful individuals and to capture Vander Decken IX, Neptune had to resort to allowing his sons and the Neptune army to arrest him, which they were unable to do until Decken's defeat during the battle for Fish-Man Island. Despite the power of the Fish-Men race, the Merfolk have a much stronger hold over Fish-Man Island, with their organized military forces. To overthrow the royal family, the New Fish-Man Pirates had to plot and form an alliance to achieve their goal. Mermen also seem to have developed a fighting style unique to their race (like Fish-Man Karate) known as Merman Combat which seems to involve the manipulation of water. As with humans, they can utilize Haki, as Otohime was born with Kenbunshoku Haki.
In case of fighting seriously, merfolk can change the course of sea currents and even generate a maelstrom as evident when the Sun Pirates battled against the Big Mom Pirates in order to save the Straw Hats.
Early One Piece
An early setting of One Piece, as revealed in One Piece Green: Secret Pieces, said that if merfolk were to soak in enough water, they would return to their once beautiful forms.
Translation and Dub Issues
Often the term "fish-men" is mistranslated from Japanese to "mermen", however the two species are very different. This is because the Kanji for fish-men (魚人) is just the reverse of mermen (人魚). Their translated name, "manfish" is how the Japanese describe the mermen and mermaids of legend, and they do not have a word for it. This mistake was carried over to the 4Kids dub.
- Early on, Luffy drew what he thought a mermaid looked like. One was a just fish with four legs. The other was a fish standing up on two legs, looking more like a fish-man than a mermaid. When Sanji wondered if Nami was really a mermaid, Luffy just added hair and wrote Nami's name on his second sketch. Surprisingly, someone that looked like his drawing of "mermaid" Nami actually appeared in Chapter 626. However, it unknown if she was a fish-woman or mermaid since only the head and arms were seen.
- The mermen so far are notably a lot less attractive than their female counterparts and so far it seems to reflect the traditional views of mermen in folklore, who are usually considered much wilder and less attractive than their female counterparts.
- In folklore, Melusine is sometimes depicted as a two-tailed mermaid, although as noted a twin-tailed mermaid appears in other forms, usually holding one of her tails in each hand. This form is the basis of the logo for the coffeeshop chain Starbucks.
- Shirahoshi and Mero are the only two known mermaids to share the same fish-half, both being smelt-whiting, besides the Medaka Mermaid Quintuplets.
- One Piece Manga and Anime — Vol. 21 Chapter 195, cover story: Hatchan's Sea-Floor Stroll Vol. 12 and Episode 306.
- One Piece Manga and Anime — Vol. 62 Chapter 608 (p. 15) and Episode 527, The Mermaids' location is revealed in the infobox.
- One Piece Manga and Anime — Vol. 51 Chapter 501 and Episode 395, New tribes revealed by auction house price list.
- One Piece Manga — Vol. 83 Chapter 830 (p. 6-7), Charlotte Praline is the 29th daughter of Big Mom.
- SBS One Piece Manga — Vol. 63, Oda confirms that males do not split their tails even after 30 years old.
- One Piece Manga and Anime — Vol. 44 Chapter 423 and Episode 306, the Mermaid dream.
- One Piece Manga — Vol. 60 Chapter 594, One of the Five Elder Stars revealing the reason why Jinbe was appointed as Shichibukai.
- One Piece Manga and Anime — Vol. 8 Chapter 69 and Episode 31, Luffy drew his "concepts" of fish-men and mermaids.
- SBS One Piece Manga — Vol. 64 (p. 126), A fan points out that a individual from Chapter 626 resembles Luffy's "mermaid Nami" drawing.