Fish-Man Island

Biodata

Feature	Information
Name	Fish-Man Island
Original Name	鱼人岛
Type	Neutral Character (AI)
Affiliation	Ryugu Kingdom
Status	Active; sovereign deep-sea kingdom ruled by King Nereus
First Appearance	Chapter 48

Overview

Fish-Man Island is a kingdom located roughly 10,000 meters beneath the sea, positioned within the cavern beneath the Red Line. It is a compulsory transit point for most pirate crews traveling from Paradise to the New World because of the region's magnetic conditions. 49 50 85

The island is enclosed by a colossal bubble and supported against Eve, the Sunlight Tree, whose light reaches the deep sea and illuminates the kingdom. 49 83 Its population is primarily composed of Fish-Men and merfolk, though the Ryugu Kingdom also recognizes citizens of other races within its territories. 262

Under Nereus, Fish-Man Island expanded from a single deep-sea settlement into an interconnected, honeycomb-like complex of subsidiary islands linked by bubble pipelines and underwater transit routes. Its strict border regime and aquatic military advantages have made it an insulated, orderly haven despite continuing turmoil on the surface. 182 270 378

Geography and Environment

• Deep-sea location — Situated in the Red Line's underwater cavern, on the route between Paradise and the New World. 50 85
• Bubble enclosure — A massive bubble membrane surrounds the island, allowing air-breathing visitors to enter while maintaining the underwater environment outside. 49
• Eve, the Sunlight Tree — A giant tree against which the island is suspended; it channels sunlight to Fish-Man Island. 49 83
• Coral Hill — A populated area containing lodging and commercial facilities. 72
• Gyoncorde Plaza — A large northwest plaza near Mermaid Bay, Coral Hill, and Yufli Villa. It serves as the island's primary public gathering place and hosted Nereus's accession announcement. 77
• Sea Forest — Receives wreckage from pirate ships destroyed near the island. It also contains a Road Poneglyph and a Poneglyph bearing Joy Boy's apology to the Mermaid Princess and Fish-Man Island. 81 338
• Fish-Man District — Originally an orphanage and later a dim, neglected slum outside the island's main bubble. Its residents were relocated under Nereus, while the former district became a training ground. 51 176
• Ryugu Palace — The royal palace and a major governmental and military site; its former grand hall was converted into a training ground. The palace's bubble membranes allow it to shift between aquatic and dry environments. 74 81 83
• Subsidiary islands — Artificial bubble-supported districts constructed around the main island for schools, housing, and infrastructure. They are linked by bubble tubes and do not possess independent magnetic fields. 83 182 270
• High-speed waterways — Bubble-pipe routes containing powerful currents that enable Fish-Men and merfolk to travel through the island at greatly increased speed. 126

Population and Races

Fish-Man Island is home to Fish-Men and merfolk, whose aquatic physiology gives them a decisive advantage beneath the sea. Fish-Men are naturally capable of breathing underwater and are several times stronger in aquatic combat than on land. 3

The kingdom's recorded population was approximately 4.15 million during Nereus's early reign. Its growth had previously remained slow because of the island's insecurity, though improved safety, housing, and welfare programs were intended to reverse that trend. 80 176

Group	Known traits
Fish-Men	Possess average arm strength ten times that of humans; many inherit species-specific traits such as camouflage, tooth regeneration, corrosive secretions, protective membranes, or flight. 14 21 78
Merfolk	Generally faster swimmers than Fish-Men; female merfolk can split their tails into legs after age thirty, while male merfolk retain fish tails. 3 84
Flying Fish-Men and merfolk	A rare group capable of sustained aerial travel using their large flying-fish traits; 209 were identified in the national census. 78 124
Non-aquatic residents	The kingdom's territories include citizens who are neither Fish-Men nor merfolk, particularly in Delta Island, Sabaody, and parts of the North Blue. 262

Fish-Men and merfolk possess a wide range of fish-species traits, which may differ unpredictably between parents and children. Such traits can include chemical secretion, camouflage, sensory abilities, and rapid regeneration; they are distinct from Devil Fruit powers. 14 21

Government and Administration

Ryugu Kingdom

Fish-Man Island became the Ryugu Kingdom after Nereus overthrew the former royal family and declared himself king. He presented the change as the end of the island's era of insecurity and misfortune. 77 78

• King: Nereus. 78
• Princesses: Nanamo and Chloe are identified as daughters of Nereus. 174 338
• Heir: Nanamo is Nereus's legal first heir. 80
• Former royal family: Removed from power during Nereus's takeover. Neptune departed the island with Pontus's body and loyal retainers after the coup. 74 76 77
• National census: Nereus ordered a census of citizens' fish species and innate abilities, prioritizing identification of potential Flying Fish units. 78
• Administration: Nereus dismissed and replaced ministers who could not support his reforms, while retaining certain experienced officials to manage civil affairs. 80 156
• International status: The kingdom became an official World Government member nation and obtained agreements prohibiting Fish-Man and mermaid slavery. 135 151
• External agreements: Several nations signed documents promising equal treatment and settlement rights for Fish-Men and merfolk. 160
• World Government arrangement: The World Government recognizes the kingdom's authority to regulate the deep-sea checkpoint and cooperate selectively against pirates and underworld interests. 119 148

Security and Entry Controls

Ships entering Fish-Man Island lose their exterior coating when it is absorbed by the island's surrounding bubbles. Leaving requires recoating by local Fish-Men or merfolk craftsmen, allowing the kingdom to control departures and prevent kidnappers from escaping. 78

• Entry requires inspection and, later, a permit for ship coating. 78 181
• Clear signage and illustrated rules are maintained at the Sabaody office for incoming travelers. 252
• Pirates pay a transit toll of 100,000 Beli per person. 84
• Travelers can purchase New World Log Poses and other supplies unavailable elsewhere. 84 345
• Unauthorized ships are intercepted or sunk by patrols. 147 338
• A sea prohibition order temporarily closed the island to all non-citizens. 146
• Ships holding valid permits are tracked by their anticipated dive and arrival times, enabling patrols to direct them safely through the kingdom's waters. 182
• The strict checkpoint system is sufficiently effective that an unsanctioned hostile entrant is generally presumed to have received high-level approval. 379

Military

Neptune Army

The Neptune Army is the Ryugu Kingdom's military force. Under Nereus, it was reorganized around the island's underwater advantages, citizen abilities, sea beasts, and elite combat units. 78 82

• Patrols protect the island's perimeter and enforce transit regulations. 84 338
• Recruits are assessed through Conqueror's Haki and tasked with subduing Fighting Fish to prove their suitability. 82
• Sea beasts are employed to destroy ship coatings and disable hostile vessels. 84
• Military training incorporates physical conditioning, specialized diets, Fish-Man Karate, and practical combat. 127 197
• The standing army reached approximately 50,000 personnel, leading Nereus to favor a separate militia system rather than continued standing-force expansion. 153
• Retired Neptune Army soldiers enter the reserves and commonly fill public-facing security and service positions, ensuring that even civilian establishments can respond to pirate disturbances. 380
• The army's ordinary units can destroy pirate ships in the deep sea without requiring intervention from senior officers. 378

First Legion

The First Legion was formed to train the future Neptune Army.

• Commanders: Sebastian and Fisher Tiger. 83
• Recruitment method: Candidates earn recognition by subduing Fighting Fish rather than merely killing them. 82 83
• Training base: Ryugu Palace's former grand hall. 83

Royal Guard

Following the national census, Nereus selected 57 eligible Flying Fish-Men and merfolk for a military draft and Royal Guard training program. 124 127

Unit	Personnel	Purpose
Royal Guard	57 recruits	Elite defense force drawn from Flying Fish-Men and merfolk of suitable age. 124
Flying Fish Army	Not specified	Aerial unit used to train recruits such as Alber. 129
Scout force	Led by Rachel	Perimeter reconnaissance, sea-beast patrols, and underwater interception. 84
Stealth company	Not specified	Uses camouflage and mimicry traits for covert underwater operations. 194 197
Militia	Not specified	Citizen defense force trained in weapons use, ship sabotage, and basic combat without replacing ordinary occupations. 153 154

Economy

Fish-Man Island's location and underwater capabilities make it a major trade and logistics center.

• Transit trade — Merchants exchange surface-world goods for deep-sea products, including pearls, coral, and rare fish. 50
• Transit tolls — Fees imposed on pirates and other passersby provide substantial income with low operational cost. 84 135
• Deep-sea salvage — The Fish-Man Pirates' primary early revenue source was recovering treasure from sunken ships and ancient ruins. 53
• Coating services — The kingdom controls essential ship-coating permits and approved coating services through Fish-Men and merfolk artisans. 78 125 181
• Security and escorts — Fish-Man Island offers protected shipping routes, insurance, and maritime security to external nations and businesses. 160 238
• Construction and infrastructure — Citizens with terrain-related abilities assist in excavation, canals, foundations, and other large projects. 239
• Research — Wobigon's work includes Sun Tree Eve cultivation and strengthening Red Yarukiman resin. 53
• Timber supply — The kingdom supplies timber to shipbuilders, especially in Sabaody and Water 7, where its flag and protective services have become valuable commercial safeguards. 235 238
• Insurance — Ryugu Insurance provides vessel insurance, escort arrangements, and debt-collection services. 238 313
• Tourism and entertainment — The kingdom operates tourism ventures, including the successful Ryugu Park in the East Blue and travel routes associated with Sabaody and Dressrosa. 306 332 381
• Industrial expansion — Because Fish-Man Island's deep-sea environment limits large-scale heavy industry, the kingdom established industrial and commercial operations in allied external territories. 172

Infrastructure and Development

Following Nereus's accession, Fish-Man Island began rapid domestic development.

• New bubble zones were created for schools and infrastructure. 83
• The Fish-Man District's displaced residents were moved into more suitable housing. 176
• New care facilities were established for abandoned children and returning overseas residents. 176
• The kingdom expanded commercial operations to Sabaody Archipelago and Water 7. 125 306
• Fish-Man Island supplied timber to shipbuilders and became a commercial lifeline for businesses in Sabaody. 238
• The island's residents experienced greater safety and stability despite escalating piracy in the outside world. 123 228
• New branch islands and bubble corridors transformed the kingdom into a three-dimensional cluster of deep-sea districts rather than a single isolated island. 83 182 270
• Fish-Man Karate and Merfolk Karate schools were established to develop the next generation and prepare citizens for emergency defense. 92 153
• An underwater commuter train links Delta Island and Fish-Man Island. 386
• The kingdom's researchers are developing a Pluto project, including work on the warship's hull and energy source, while concealing much of the program behind public entertainment projects. 394

External Territories and Influence

Sabaody Archipelago

Fish-Man Island obtained the Lawless Area of the Sabaody Archipelago through an agreement with the World Government. 119 123

• Babel established a Ryugu Kingdom overseas office and occupied a former Marine station. 125
• The kingdom protects cooperating coating artisans in return for servicing only approved ships. 125
• Although the Navy still considers it lawless, Fish-Man Island's management made Sabaody one of the safest nearby locations. 238
• Sabaody serves as a training ground for Fish-Man Island's younger generation. 123
• The kingdom's control expanded from part of the mangrove islands to nearly all groves except World Government offices and the Marine base. 394
• The overseas office employs both Ryugu personnel and rescued human civilians who settled in Sabaody after trafficking rings were dismantled. 238
• Fish-Man Island offers escorted underwater passage from Sabaody to the deep-sea kingdom. 252

Delta Island

Delta Island is a settlement territory associated with Fish-Man Island. It hosts the annual Day of Rebirth, commemorating the freedom and new lives of those first settled there by Nereus. 112

The island is connected to Fish-Man Island by an underwater commuter train and functions as a resettlement site for displaced people and returning residents. 108 386

Other Operations

• North Blue — Fish-Man Island maintains influence through Fisher Tiger, who serves internally as the Ryugu Kingdom's Governor-General to the North Blue, as well as later personnel deployments. 179 235 306
• Water 7 — The kingdom acquired property and recruited staff as commerce revived around the Sea Train. 306
• East Blue — Arlong's Ryugu Park operates successfully there. 306
• Dressrosa — Fish-Man Island maintains commercial and tourism links with Dressrosa, including underwater-development and escorted travel projects. 332
• Dole Kingdom — An allied nation that hosts Ryugu Kingdom-supported industrial and development operations. 172

History

Before Nereus's Rule

Fish-Man Island's former rulers failed to adequately protect the population from pirates and slave-catching crews. The Fish-Man District deteriorated from an orphanage into a lawless slum, while powerful Fish-Men and merfolk often pursued lives abroad rather than defend their homeland. 26 51 176

The island's strategic route made it valuable to merchants, pirates, smugglers, and traffickers. Its prior weakness reduced the risks faced by slave traders and left residents vulnerable. 50 51

Nereus's Takeover

Nereus arrived at Fish-Man Island, confronted smugglers, reconnected with the Fish-Man District, and began gathering local fighters such as Fisher Tiger. 51 52 He subsequently entered Ryugu Palace, informed King Pontus of his intention to overthrow the royal family, and learned that Poseidon could be reborn as a mermaid princess on the island. 74

Nereus publicly declared himself the new king, promising to replace the island's history of darkness with a secure and powerful nation. 77 78

Consolidation

After taking power, Nereus reorganized the military, conducted a nationwide census, established patrols, recruited Fighting Fish partners, built new infrastructure, and imposed transit taxes. 78 82 83 84 The kingdom's deterrence sharply reduced pirate activity through the deep-sea route. 72

Nereus further centralized control of entry and exit by regulating coating permits, developing military schools, and expanding the island through subsidiary bubble districts. 83 181 182

International Recognition

Fish-Man Island entered agreements with the World Government, including a ban on Fish-Man and mermaid slavery. 151 It also received authority over Sabaody's Lawless Area, allowing the Ryugu Kingdom to develop an overseas office, regulate coating services, and expand its commercial reach. 119 125

At the Reverie, Nereus secured additional agreements with foreign nations concerning equal treatment, settlement rights, commercial security, and protected shipping routes. 160

Sea Prohibition Order

Nereus temporarily sealed Fish-Man Island to non-citizens while pursuing the trafficker Harding. The resulting blockade stranded pirate and underworld traffic, demonstrated the Neptune Army's ability to enforce the deep-sea route, and significantly strengthened the kingdom's deterrent reputation. 145 146 147 153

Later Era

Fish-Man Island remained insulated from the worsening pirate crisis after Roger's execution, with pirate wreckage and aggressive patrols discouraging incursions. 228 338 Its reputation became strong enough that even major pirate crews were expected to obey local regulations. 356

Following the Summit War and the Impel Down breakout, Fish-Man Island continued to function as an isolated deep-sea paradise. Pirates who attempted to force entry were swiftly destroyed by ordinary Neptune Army patrols and sea beasts, while internal life remained largely unaffected by the surface world's instability. 378 379

Notable Residents and Personnel

• Nereus — King of the Ryugu Kingdom; led the overthrow of the former royal family and transformed the island's military, economy, and external relations. 74 78
• Nanamo — Nereus's daughter, legal first heir, and princess; participated in recruitment and island affairs. 80 82 85
• Chloe — Nereus's hybrid Fish-Man/Lunarian daughter; later assists with entrance security. 174 338
• Sebastian — Fish-Man officer, First Legion leader, and specialist in camouflage-based operations. 83 194
• Fisher Tiger — Former Fish-Man District boss and First Legion leader; later serves as the kingdom's Governor-General to the North Blue. 51 83 179
• Sunbell — Fish-Man commander involved in the island's defense and later a school instructor. 72 194
• Rachel — Electric Ray Mermaid and scout captain responsible for perimeter patrols. 84
• Babel — Ryugu Kingdom operative stationed at Sabaody Archipelago. 125
• Wobigon — Scientist and Nereus confidant researching ancient technology, botany, Sun Tree Eve, Red Yarukiman resin, and lineage-factor technology. 53 394
• Tom — Fish-Man shipwright with ties to the kingdom; assists Nereus with ship-destruction techniques and Pluton-related materials. 127
• Arlong — Fish-Man operative and proprietor of the successful Ryugu Park amusement enterprise in the East Blue. 301 306
• Alber — Lunarian recruited by Nereus; trained with the Flying Fish Army and later assists Wobigon's research. 129 394
• Shyarly — Mermaid Cafe proprietor and former military-trained resident responsible for maintaining order among visiting pirates. 380

Trivia

• Fish-Man Island's waters are sufficiently difficult to navigate that a local guide can be valuable even for pirate crews descending in coated ships. 345
• The kingdom's Fish-Man Pirates are treated as a prestigious historical institution; their emblem is used as a symbol of honor by later Ryugu Kingdom personnel. 299 338
• Fish-Man Island's geography makes it hard both to enter and to leave, giving its government unusual control over ship traffic. 78
• Its deep-sea position is also a natural military advantage: Fish-Men and merfolk can travel faster and more covertly than ships underwater. 194
• Despite its former isolation, Fish-Man Island is one of the few locations where Fish-Men and merfolk can openly operate extensive businesses and public institutions with state protection. 238 381
• The island's civilian service personnel frequently include former Neptune Army soldiers, making seemingly ordinary venues dangerous places for pirates who disregard local rules. 380