Mermens

Mermens (魚人, Gyojin) are one of the species that dominate the seas (the other being the mermaids and fishfolks). In terms of leadership, King Neptune is the king of Merman Island. Tiger Fisher, Jimbei, and Arlong were said to have the highest respect amongst their people. The slave price would be shown as, 1,000,000 berries.

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 * —About Mermens.

Appearance
Appearance-wise, they are more "Hybrid species" than mermaids, looking like a cross between a man and a fish of the ocean such as a whale shark, manta ray, or sawshark; however, they still have legs (in fact, Decken has four). They also have gills between their shoulders and necks, sometimes covered by their clothing, as well as most having webbed hands. Depending on species, they may have multiple limbs (mainly extra arms).

Size may also differ greatly between individuals, as Arlong was much taller than any of his crew members, while Wadatsumi is easily larger than the giant-sized Shirahoshi.

For mermen pirates in pirate crews that are primarily merman based, (Sun Pirates, Arlong Pirates, and New Mermen Pirates) it is customary to have that crew's jolly roger tattooed somewhere on the person's body, showing allegiance to a crew.

Biology
Mermen have their gills near their necks which only work when they are in water. On land they can breathe with their lungs like humans do. However, their gills cannot breathe in air, like a normal fish cannot breathe in air through their gills.

Even though mermen are part fish, they are still mammals and give birth to live young. Mermen can also interbreed with other races: as was revealed during the Davy Back Fight Arc with Big Pan, mermen can breed with giants, producing a hybrid who the has biological abilities of a merman and the huge body of a giant (but still smaller than a full one, as related by Robin), they are known as wotans. Pappug explained that mermen (mermen and merwomen; of female mermen) can have children with other of its sea species (manfish and mermaids); however, the child's race is up to chance between mermen, mermaid and fishfolk. There are many mermaids who bear physical traits normally unique to mermen, like Den's webbed hands and Sharley's fangs. Furthermore, mermen can sometimes demonstrate powers usually unique to mermaids and fishfolk, such as Jimbei's ability to communicate with whale sharks.

Even with merman, mermaid and mermen in the same immediate family, the primary species (mermaid, fishfolk or merman), subspecies (type of fish) and appearances may differ. The reason is that they still carry the genes of their ancestors, so the species is not determined only by the parents, but it can be any one type among all the species of the ancestors. It is also possible for humans and mermen to interbreed, as Sapi is a result of such. Humans, mermen, mermaid, and fishfolk also share the same blood types.

The mermen's subspecies have many variations, just like mermaid and fishfolk, being many types of fishes. So far, all known mermen fish-halfs are based on real-life fish species and not on any of Oda's made up species. Also, their size may vary greatly, with Wadatsumi being a merman the size surpassing that of an average giants. Unlike mermaids of fishfolk, mermen eat meat including fish.

Known Mermen and Their Species

 * Arlong: Sawshark
 * Chew: Smelt-whiting
 * Hatchan, Octopako, Karma: Octopus
 * Kuroobi: Ray
 * Kaneshiro: Goldfish
 * Pisaro: Ocean Sunfish
 * Take: Carp
 * Shioyaki: Salmon
 * Macro: Pelican Eel
 * Gyaro: Pop-eyed Goldfish
 * Tansui: Arowana
 * Big Pan: Loach
 * Capote: Billfish
 * Tom: Cowfish
 * Jimbei: Whale shark
 * Hammond: Daggertooth Pike Conger
 * Kasagoba: Marbled Rockfish
 * Hordy Jones: Great White Shark
 * Dosun: Hammerhead Shark
 * Zeo: Japanese Wobbegong Shark
 * Daruma: Cookie-cutter Shark
 * Ikaros Much: Giant squid
 * Decken Vander IX: Japanese Bullhead Shark
 * Wadatsumi: Giant Tiger Blowfish
 * Tiger Fisher: Sea Bream
 * Willy (Film): Orca
 * Jube (Filler): Squid
 * Nuru (Filler): Anglerfish

Inter-species Relationships
Despite their beliefs, they usually get along well with the mermaids and fishfolk who share the opposite view on life, however it is not unknown for mermen to take advantage of the mermaids's nature.

Stereotypical mermen consider humans to be an inferior, weaker species. However, this does not apply to all mermen. For example, Tom, cared for and looked after two humans (Iceburg and Franky) and even protected them from the actions of Spandam and CP5. Another example is Jimbei, who considers Ace D. Portgaz an equal and holds the Whitebeard Pirates in high regard because of Whitebeard protecting Merman Island. Jimbei would later feel the same way about Ace's younger brother, Luffy D. Monkey. Tiger Fisher was noted to hate humans but not to discriminate when it came to slaves. When he broke into Mariejoa to free the merman slaves, he also freed the other races as well. Additionally Tiger Fisher did not wish to kill any humans for their discrimination because it would only cause more anger and resentment, and even personally returned a human slave girl back to her home.

Furthermore, when the Straw Hats were suspected of having kidnapped several mermaids from Mermaid Cove (actually Caribou's doing), it had been seen that at least some merman citizens insisted that the pirates should not be convicted without solid proof implying that at least some mermen are willing to grant humanity the benefit of a doubt.

On the opposite end of the spectrum, human relationships towards mermen was defined with their definition of them, mermaids and fishfolk as "fish" instead of "men". This lead to centuries of discrimination as the mermen fought to prove their worth to the world. Only two hundred years ago did the World Government begin to bridge the gap by making an alliance with Merman Island to remove the problems between the two sides. Jimbei's appointment to the Seven Warlords of the Sea was an attempt to strengthen the bonds between the races but due to his resignation it ended in failure. While attempting to fix the problem, centuries of bad relations remained. Many humans continued to see mermen as freaks or in the case around Sabaody Archipelago, slaves for the World Nobles. Such bad relations between the races would influence certain sects of mermen, these mermen would even go so far as to return to the humans what had been done to them. This was seen once in the series with Arlong Park in East Blue where Arlong attempted to enslave the humans as they had enslaved his men and he succeeded in doing so for eight years. Humans have also made a law that forbids humans from donating blood to mermen and vice versa. Most people believed this is what caused Tiger Fisher's death. The truth is he refused a blood transfusion using human blood because he did not want their hatred for his race flowing through his veins so he refused to owe them his life. However not all humans are predujiced against merman. For instance, Hancock Boa, who generally hates males, showed respect and gratitude towards Tiger Fisher for the debt she owed him for freeing her along with her sisters. She also seems to respect Jimbei, to a certain degree, allowing him to set foot on Amazon Lily. Another example is Koala who formed a special bond with the Sun Pirates and even promised them she'd tell the people of her village that merman are nice people.

Because of their huge biological differences, they have failed to completely understand the human view of family and the habit of categorizing individuals. Humans have also failed to understand the mermen, mermaids and fishfolk differences.

After the assassination 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 Merman Island to dream of the sun.

However, it was later revealed in the conflict with Hordy Jones and the New Merman Pirates, that despite all their efforts, the Merman District had been a breeding ground for hatred for Humans. Even with the Straw Hat Pirates fighting for Merman Island, an adult can be seen attempting to tell the children about the human oppression that has been occuring throughout history. Sharley interrupted him and told the children to draw their own conclusions based on the events they were witnessing.

Mermen are worth an average of 1,000,000 berries in the slave market.

Overall Strength
They are physically ten times as strong as normal humans from birth and this difference is magnified underwater, where a human's power is cut in half, while merman not only are completely unhindered, but are even strengthened. Jimbei himself noted that on dry land he had little power to offer, which considering the strength that even a merman as powerful as he has speaks volumes about the potential of any merman in the water compared to being on dry land. As a whole, in the midst of battle, the merman race can be considered unstoppable in their natural habitat - the sea. As well as being powerful they can still talk under water and cannot drown. However, breathing air into their gills makes them suffer like a normal fish would. While they can use their gills to breathe in water, they have to switch back to their lungs to breathe in air.

Like Mermaids, Mermen also possess the ability to communicate with sea creatures. In particular, Mermen seem adept at communicating with large sea monsters, and possess a unique capacity to bring out the primal rage in such creatures. This ability was first demonstrated when Arlong induced Momoo into a primal frenzy to have him attack the Straw Hats during the battle at Arlong Park, even despite Mohmoo's initial reservations about doing so. The ability was shown again in more detail when Hordy and to a more limited extent, the officers of his crew as well, used it to induce the large Sea Monsters the New Merman Pirates had in their possession into a similar red-eyed rage to the one created by the Energy Steroids they had been eating. Of course, the animal being induced has to be at least somewhat willing to comply, as was shown when Surume quickly stopped squeezing Shirahoshi due to Luffy's intervention, and afterwards refused to follow any more of Hordy's orders. Lastly, it should be noted that just as with Mermaids, Mermen are still for some reason unable to communicate with Sea Kings; the Mermaid Princess, currently Shirahoshi, is supposedly the only one capable of doing that.

The Merman Dojo of Merman Island is also where they learn Merman Karate, a number of mermen have displayed skill in this fighting style already within the storyline. This fighting style in particular has both land and sea based attacks, a style suited to the mermen's advantage in the water, but does not leave them completely unable to defend themselves on land when they have to. Their most effective weapon is the sea itself as the most powerful fighters can take a few drops of water and hurl it so hard the impact is as hard as a bullet. To this extent, at the hands of a powerful merman, even a small splash of water becomes a lethal weapon. As expected they are excellent swimmers, they are capable of swimming through the water at a great speed and force, their speed however is no match for the mermen who are the fastest.

Mermen often have unique abilities, matchings those of the species they are based on, that make them further superior to ordinary humans outside of the physical strength difference. Hatchan's six arms give him a huge advantage over most fighters with just two arms and he can spit ink. Chew as an archer-fish could shoot water from his mouth like a bullet. Arlong as a sawshark merman could regrow his teeth after they broke. Zeo is a Japanese wobbegong who can camouflage himself, almost like a certain Cursed Fruit ability. Though only a half breed, Big Pan inherited slippery skin from his mudfish merman heritage, which is also like a certain Cursed Fruit. Both Zeo and Big Pan have demonstrated that a merman's ability can be akin to that of an actual Cursed Fruit's. Members of the shark family have been seen as particularly fearsome fighters and Arlong, Jimbei, and Hordy Jones, three of the strongest known mermen are all shark-based breeds. The New Mermen Pirates have a notably large number of officers that are shark breeds and the only merman amongst the Whitebeard Pirates, Namur, is also a shark merman. The shark based breeds were confirmed to be considered a fear to the other citizens on the island when Daruma attacked the candy factory, the citizens also expressed concern over the squid merman in the crew, Ikaros Much, indicating that this type of merman was also a cause for concern.

Like giants, they have yet to display the use of skills such as Haki. Their reaction to consuming a Cursed Fruit is the same as it is for humans, rendering them unable to swim, and must wear a bubble to compensate. However, their water-based abilities prove most helpful considering that in water, Cursed Fruit users are rendered completely powerless. The Cursed Fruit Shadow-Shadow Fruit in particular has little advantage at all against a merman who knows its fatal weakness, salt. Arlong commented on Nami's navigation skills, stating that they can learn about navigation very easily, but they cannot find a good navigator. This remains unexplained as to why they are particularly weak in this area but does indicate their race has an overall weakness in skillful navigation. Arlong himself in particular came to admire Nami's own skills, and in a rare act considered her skills on par with the merman "superiority", confessing that she simply could not help what species she was.

Because of their strength, they appear in the series on a regular basis. However, Jimbei was noted to have acknowledged the strength of Neptunians on one occasion, thus proving even their race is aware of the danger of Neptunians in the Grand Line.

Beliefs
Their view of life under the sea is dominated by their views that they should rule over all other fish in the sea. They also hate humans for the years of oppression and slavery that they suffered. This is not shared among all mermen, though, as Tom, Jimbei, and Tiger Fisher have respect for humans and other races. It can also be assumed that Namur, as a commander of the mostly human Whitebeard Pirates, does not share this prejudice against non-mermen. However, the New Merman Pirates, specifically the officers and captain, took this hatred to irrational levels, due to being raised in an environment that basked in the hatred, despite not being subjected to any oppression themselves, and they were fully willing to die and destroy their own bodies to achieve their "revenge", in fear of the day that humans and fish folks would coexist and cease their animosity. Due to the long-term neglect in the Merman District, this hatred has been passed down to future generations since the past, resulting in the New Fishman Pirates being the most prominent example of meaningless hatred.

Many of the mermen, particularly of note the pirates, also adorn symbols across their bodies to represent their group association. So far the marks they have adorned include the Sun Pirates' "mark of the sun", the Arlong Pirates' jolly roger, a tattoo of unknown significance, and the New Merman Pirates' jolly roger of a beheaded human crossed out with the "mark of the sun" surrounding it. Kaneshiro, Pisaro, Take, Shioyaki, Namur, and Tom also had other tattoos on their bodies.

Pirates

 * Arlong Pirates
 * Arlong
 * Chew
 * Kuroobi
 * Kaneshiro
 * Pisaro
 * Take
 * Shioyaki
 * Whitebeard Pirates
 * Namur
 * Karma
 * Macro Pirates
 * Macro
 * Gyaro
 * Tansui
 * Foxy Pirates
 * Capote
 * Jube
 * Girarin
 * Seven Warlords of the Sea
 * Jimbei
 * New Merman Pirates
 * Hordy Jones
 * Dosun
 * Zeo
 * Daruma
 * Ikaros Much
 * Hammond
 * Kasagoba
 * Harisenbon
 * Nuru
 * Flying Pirates
 * Decken Vander IX
 * Wadatsumi
 * Sun Piatres
 * Tiger Fisher
 * Willy
 * Golden Lion Pirates
 * Kitajima
 * Gad

Citizens

 * Sapi
 * Tom
 * Hatchan
 * Octopako
 * Ammo Knights
 * Junan
 * Papaneel
 * Togare
 * Hack

Anime and Manga Influences
Mermen were developed from the concept of the reverse mermaid, who had a fish upper half and human lower legs. Oda confirmed details about their race in a SBS corner and how instead of the fish half being centered around the tail end, it was focused instead on the upper half of the body.

The Fishfolk and Merman conflict with humans bears a striking resemblance to the events of the Manga/Anime series Blue Submarine No. 6. In the series, a scientist named Zorndyke had witnesed his own family killed via racial purging prior to the storyline. He created a new race that were hybrids of human and the DNA of various Marine lifeforms. Zorndyke started a war between his "children" and mankind as a form of punish to mankind for its immoralities. Zorndyke's "son" and general, Verg, had qualities shared by both Arlong and Hordy Jones. Verg preached and believed in superiority over humans and led a crew that wiped out many great cities, killing millions in the process while under the belief his "father" was creating a world for them. The reality was the new species was meant to rival, not wipe out mankind and the war was nothing but a test. When the conflict ended, Verg was given the chance to meet humans face to face, however, Verg decided humanity had nothing to offer him and refuse to speak to them rather then take the chance to settle their differences.

Trivia

 * Early on, Luffy drew what he though a mermaid looked like. The first was a just fish with four legs. The second was a fish standing up on two legs, looking more like a merman than a mermaid. When Sanji wondered if Nami was really a mermaid, Luffy added hair to his second sketch and wrote Nami's name. Surprisingly, someone that looked like his drawing of "mermaid" Nami actually appeared in Chapter 626. However, it unknown if she was a merwoman or mermaid since only the head and arms were seen.
 * Originally Oda planned on introducing mermen as far back as Chapter 3. However, due to his editor he then put it back, ending up introducing the concept during the Arlong Park Arc instead.
 * So far, Decken Vander IX is the first and only merman known to possess a Cursed Fruit ability. He is also the only merman who cannot swim (due to the Cursed Fruit).
 * There was originally going to be a starfish merman named Hitodenashi (ヒトデナシ, Hitodenashi), a member of the Arlong Pirates and Hatchan was originally going to be a squid merman named Maple Reed (メープル・リード, Meepuru Riido).