ENGLISH SOURCE COMPANION / JMA · SEPTEMBER 2025
Medaka Trait Classification: English Research Notes
The Japan Medaka Association published the fifth edition of its variety classification manual in September 2025. These original notes index research topics from private working English adaptations; they do not replace the Japanese publication. The source explicitly reserves translation, modification, copying and public redistribution rights.
- Japanese source pages Selected opening pages · Original English editorial explanationOpening selections
English research summary (not a translation)
The JMA manual uses a traits-first way to describe improved medaka. A breeder's nickname can remain useful for identifying a particular line, but an objective description also needs the visible body color, scale transparency, body form, eye structure, and fin characteristics.
Recording both the Japanese strain name and these diagnostic traits makes the same fish easier to compare across breeders, languages, shows, and marketplaces. A named line's pedigree remains a separate evidence question.
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- Japanese source pages 17–36 · Original English editorial explanationBody color, transparency, eye structure
English research summary (not a translation)
Color is only one part of a medaka's identity. Two fish can look similar in a photograph while differing in scale transparency, pigment distribution, or eye construction. Examining both top-view and side-view appearances helps prevent a trade name from being mistaken for a diagnostic trait.
Use stable conditions when comparing photographs. Record background color and lighting, the age of the fish, whether the look is consistent across siblings, and the breeder's documented parentage when available.
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- Japanese source pages 37–38 · Original English editorial explanationEye variants
English research summary (not a translation)
Big Eye describes the diameter of the eye itself rather than an eyeball that projects outward. Bubble Eye involves a bubble-like change in the corneal area. Earth Eye refers to blue or silver-looking pupil coloration, while Platinum Eye has sparkling patches on the cornea.
These names describe distinct visual structures: eye size, corneal shape, pupil appearance, and reflective highlights. When evaluating fish, photographs taken from consistent angles are more informative than simply labeling all unusual eyes as 'blue eye' or 'big eye'.
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- Japanese source pages 39–40 · Original English editorial explanationReflective scale traits
English research summary (not a translation)
Lame is the glint produced on individual scales; external body light describes a more continuous reflective region along the fish's back. They can occur together, but one does not automatically prove the presence of the other. A fish with bright scales should therefore be described with the actual distribution of its reflections.
The JMA reference associates the spread of dense lame with selective development of Miyuki-related external-light lines. When recording a specimen, note its viewing angle, the number and color of reflective scales, and whether dorsal light reaches toward the head.
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- Japanese source pages 43–44 · Original English editorial explanationInternal body light
English research summary (not a translation)
Internal body light is a luminous-looking effect seen within the body rather than on the outer scales. The JMA history places an early pale blue-white form at a 2008 exhibition. Its internal reflective layer is most evident from above, and much harder to observe from the side. Later selective breeding extended the visibly illuminated region toward the pectoral fins; stronger examples were often marketed as Super Internal Light.
The manual distinguishes blue-white, green, orange, blue and multicolored expressions. A constant orange appearance is different from a transient color shift after the fish is disturbed. It also distinguishes regular internal light from Whole-body Internal Light (often brighter, broader, and associated with transparent or semitransparent scale expressions) and Peritoneal Light (concentrated around the abdominal lining).
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- Japanese source pages 47–48 · Original English editorial explanationBlack marks and patterning
English research summary (not a translation)
Buchi describes separate black patches, which may appear at different places and strengths on the body. Nishiki is often used in trade names for multicolored forms, but the visible black-patch trait is not the same as proof of a particular breeding line. Selective breeding can increase both the spread and the intensity of patches.
Black Rim forms a more continuous dark emphasis around and across scales, rather than separated blotches. In some examples, the dark effect changes from scale edges near the head to centers closer to the tail. Background response matters: some black markings fade in pale containers, while selected forms such as the reported Wazumi line can retain their darkness more reliably.
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- Japanese source pages 54–55 · Original English editorial explanationClassic long-finned forms
English research summary (not a translation)
Hirenaga (Long-finned) is the form in which the overall fins are markedly extended, including the webbing. The JMA attributes the classic Matsui Hirenaga to Katsujirō Matsui in 2015. Long Fin, by contrast, chiefly describes extended dorsal and anal fin rays; the membranes do not necessarily extend with them.
Wide Fin concerns width and structural dimensions rather than simply length. Real Long Fin retains the underlying shape of the fins as they extend, unlike some rounded long-fin expressions; the manual describes the proportional length threshold as about one and a half times normal. These distinctions are easiest to see in well-focused side-view images.
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- Japanese source pages 56–57 · Original English editorial explanationAdditional fin variations
English research summary (not a translation)
Morpho has a fan-shaped caudal fin with saw-toothed or serrated ends, and similar edges can occur on other fins. Fusa-fin describes branching fin rays that make a tufted appearance. Both differ from a straightforward increase in fin length.
Narrow Fin is identified mainly by the reduced apparent width of the anal fin, not necessarily a lower ray count. In the JMA account it was reported by Takayasu Ōba in 2022 and has a more rounded, delicate impression. Document the entire fin silhouette before using any of these names.
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- Japanese source pages 58–60 · Original English editorial explanationHikari and Daruma forms
English research summary (not a translation)
Hikari body type is marked by a diamond-shaped tail and a dorsal fin corresponding closely in form to the anal fin. It is a matter of body symmetry and fin geometry, and should not be confused with the presence of external body light. Some Hikari fish have conspicuous dorsal sheen, but not all do.
Daruma fish have shortened bodies and raised backs; the form can be more sensitive to changes in water quality and temperature. Hikari Daruma combines the two form characteristics. The appearance of a single short-bodied fish does not establish that the trait will breed true throughout its offspring.
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- Japanese source pages 61–62 · Original English editorial explanationFin color and blue peritoneum
English research summary (not a translation)
Fin beauty describes conspicuous, concentrated fin pigment that stands out from ordinary coloration. Where the vivid color occurs matters: the outer caudal edges, fin bases and other regions can look different between varieties. Merely having orange fins on an amber-colored fish is not necessarily enough to call the trait exceptional.
Blue Peritoneum describes a blue appearance associated with the abdominal lining. The source separates it from bright Peritoneal Light because their visual expression responds differently to backgrounds: blue-peritoneum coloration is easier to assess in a light container, while the bright-light trait is better revealed on a dark background.
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- Japanese source pages 63–64 · Original English editorial explanationPigment and environmental response
English research summary (not a translation)
Internal Black involves darker pigment inside the body, often visible around the spine or internal lining. Fin Light describes conspicuous reflective brightness on the fins, while light that follows the fin edges all the way around is described as a related perimeter-light presentation.
Background response can change how dark or colorful a medaka appears without changing its pedigree. The manual also recognizes selected backgrounds-resistant expressions that hold more of their pigmentation even in a white container. Record the viewing background before comparing dark fish.
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- Japanese source pages 65–67 · Original English editorial explanationEyes, transparency and powder
English research summary (not a translation)
The later trait sections distinguish small jaw protrusions associated with certain protruding-eye fish, upward-facing eyes, and Mosaic Panda expressions. These should not be bundled together simply because the eye or face looks unusual from a distance.
See-through is a highly transparent expression associated with missing reflective pigment, exposing internal structures; side-reflective light is a separate guanine-based effect. Powder describes fine white pigment-cell particles on the body surface or fins. These features should be photographed at high magnification and scored separately.
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- Japanese source pages 68–69 · Original English editorial explanationPigment deficiencies
English research summary (not a translation)
Black-pigment deficiency does not mean every pale fish has the same condition. The JMA reference distinguishes pale body-color expressions from albino-related eye and body effects. Ruby Eye and angle-dependent eye-color changes are also listed as separate visible categories.
Scale transparency and eye pigmentation interact: combinations of albino and transparent-scale appearances can reveal the internal organs more clearly. A label like Panda or See-through should therefore reflect the visible structure, not only a seller's nickname.
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- Japanese source pages 70–71 · Original English editorial explanationReported Aurora breeding lines
English research summary (not a translation)
Lineage refers to a group of fish linked by breeding across generations, whereas a trait is something recognizable in the individual fish. A common ancestor does not guarantee that every descendant expresses the same visible feature.
The source uses Aurora to illustrate this distinction. 'Aurora line' can refer to descendants of the original Aurora population; 'Aurora trait' refers to a recognizable partially transparent-scale expression. A verified pedigree and a visible phenotype should be recorded as separate fields.
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- Japanese source pages 72–73 · Original English editorial explanationAurora, multicolor naming
English research summary (not a translation)
Names such as Aurora, semitransparent scale and nontransparent scale have been used inconsistently. The manual tries to separate line membership from measurable appearance, reducing confusion when a fish bears a historic line label but does not show that line's famous phenotype.
Traditional multicolor terms such as Nishiki and Sarasa have different histories across goldfish, koi and medaka. For Aquapedia records, capture the original Japanese label, then describe the actual color blocks, black patches and scale traits rather than inferring genetics from a familiar market term.
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- Japanese source pages 74–75 · Original English editorial explanationClassification FAQ 1–12
English research summary (not a translation)
The early questions explain why a shared vocabulary matters for shows, breeder communication and strain development. A trait-based system enables two fish to be compared by visible characteristics even if the sellers use different trade nicknames.
The JMA approach is a voluntary classification framework, not a law. Breeder-created names can be retained, but pairing them with a readable trait description makes listings and records far more useful. The reference emphasizes observable traits rather than making genetic testing a prerequisite for naming every fish.
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- Japanese source pages 76–77 · Original English editorial explanationClassification FAQ 13–22
English research summary (not a translation)
These questions address how new character names are considered, why descriptive trait terms should remain distinct from house names, and how breeders can document a consistent line over several generations. Selection criteria are important: changing the target traits changes what the line is being selected to express.
The manual also introduces pigment cells and the physical movement of pigment granules. Background color can change the immediate outward appearance of a fish, so phenotype assessments need repeatable viewing conditions.
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- Japanese source pages 78–84 · Original English editorial explanationClassification FAQ 23–54 and conclusion
English research summary (not a translation)
The concluding questions put the classification principles into practice. They discuss the interaction of pigment-cell types, multicolor patterns and environmental response, with examples involving Orochi, green reflective variants, yellow versus gold, and transparent-scale naming.
The JMA treats visible characteristics and ancestral line labels as different types of evidence. This section is indexed here as an English study guide only. A private page-matched working adaptation of pages 78-84 exists but still requires figure-label localization and bilingual proofreading.
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Source: Japan Medaka Association (日本メダカ協会), 2025, fifth edition. The final page contains a copyright statement requiring prior written authorization for public alterations and reposting.