Jul 19, 202610 min read
Ranchu Conformation: How Breeders Evaluate Body and Head Author: Liu Wei, Professor of Ornamental Fish Genetics Reviewed by: Kenji Tanaka, Freshwater & Koi Specialist Date: 2026-07-19 Word count ta...
Jul 16, 202610 min read
Lionhead, Tigerhead, Oranda: A Line History of Fancy Goldfish Author: Liu Wei, Professor of Ornamental Fish Genetics Reviewed by: Kenji Tanaka, Freshwater & Koi Specialist Date: 2026-07-16 Word cou...
Jul 13, 20269 min read
Goldfish Double-Tail Genetics: How the Trait Is Inherited Author: Liu Wei, Professor of Ornamental Fish Genetics Reviewed by: Kenji Tanaka, Freshwater & Koi Specialist Date: 2026-07-13 Word count t...
Jul 11, 20269 min read
Koi Color Genetics: White, Red, Black, and Yellow Inheritance Author: Liu Wei, Professor of Ornamental Fish Genetics Reviewed by: Kenji Tanaka, Freshwater & Koi Specialist Date: 2026-07-11 Word cou...
Jul 9, 20268 min read
Marker-assisted selection is what separates hobby breeders from serious breeding programmes. Here is what it is, how it works, and what to ask a breeder before buying breeding stock.
Jun 21, 202612 min read
An ornamental-fish breeding researcher walks through the practical management of fish egg incubation — the role of temperature in development rate and phenotype, the role of dissolved oxygen in hatch success, the equipment used, the species-specific requirements for common ornamental and aquaculture species, the troubleshooting of common problems, and the four mistakes that turn a viable spawn into a dead egg mass.
Jun 13, 202612 min read
An ornamental-fish breeding researcher walks through the genetics of color in koi — the four base colors, the modifiers, the inheritance patterns, how breeders plan matings to produce specific varieties, the role of the white ground, the red and black pattern genetics, and the four mistakes that turn a controlled koi breeding project into a project that produces mostly kawarimono.
May 30, 202613 min read
An ornamental-fish breeding researcher walks through the genetics of the double-tail trait in goldfish — what the phenotype looks like at every stage, how the trait is inherited in practice, what breeders have learned from forty years of crossing data, how to plan a breeding program that produces predictable ratios, and the four mistakes that turn a controlled double-tail project into a slow slide back toward single-tail descendants.
Mar 30, 202616 min read
An ornamental fish breeder and historian walks through the native Chinese freshwater species that are well-suited to the home aquarium — bitterling, paradise fish, white cloud mountain minnow, Chinese hillstream loach, and others — with the practical care requirements and the conservation considerations.
Feb 5, 202614 min read
An ornamental fish breeder walks through the practical techniques of artificial spawning and hand-stripping in egg-laying fish — when to use it, when to avoid it, the equipment, the hormone options, and the four mistakes that lose an entire spawn.
Jan 22, 202617 min read
An ornamental-fish breeder and historian walks through the four-thousand-year arc of Chinese goldfish domestication — the original single-tail, the bifurcation into the modern fancy lines, the global diffusion through Japan, Europe, and America, and the modern lines that trace their lineage back to a Ming dynasty mutation.
Jan 4, 202615 min read
A practical genetics primer for the ornamental fish breeder — what inbreeding depression actually looks like in guppies, koi, goldfish, and bettas, why "the line is fine" is the most expensive sentence in the hobby, and the three counter-moves that keep a closed line viable.
Dec 22, 202510 min read
Modern Japanese koi breeding is a 200-year story of one region, one rice fish, and a few families who turned a working-class food fish into a $20,000 show winner.
Nov 30, 20259 min read
The Ranchu is the most difficult fancy goldfish to breed to standard. The body, the head, the wen, the swimming, and the deportment are all evaluated. Here is the breeder's checklist.
Nov 13, 20259 min read
The Glofish is the first commercially available transgenic pet animal, and the Glofish has been a commercial success. The science is real, the market is real, and the ethics are debated. Here is the full picture.
Nov 8, 20259 min read
The Taisho Sanke is a white-based koi with red and black, and the red is the pattern that is hardest to stabilize. Here is the line breeding protocol, the culling decisions, and the genetic understanding that produces consistent Sankes.
Oct 23, 20259 min read
The lionhead, the tigerhead, and the oranda are the three head-growth fancy goldfish breeds that share the wen trait. The differences are in the body, the hood, and the history. Here is the comparison.
Oct 10, 20258 min read
Sexing juveniles is harder than sexing adults, but the methods exist. Here is when each method works, which species it works for, and the accuracy to expect.
Sep 28, 20259 min read
Crossing two unrelated lines can produce offspring that grow faster, live longer, and resist disease better than either parent. It can also produce offspring that are sterile, deformed, or unexpectedly dull. The difference is in the lines.
Sep 22, 202510 min read
Line breeding concentrates the genes of a specific ancestor. Inbreeding concentrates the genes of any relative. The two are not the same, and the difference matters for the long-term health of the line.
Sep 18, 20259 min read
Triploid fish are sterile, grow faster, and survive better in some conditions. They are also more expensive, harder to identify visually, and not always the right choice. Here is the cost-benefit analysis.
Aug 22, 202511 min read
Albino koi, albino corydoras, albino Oscars, albino bettas — the albino trait is one of the most striking in ornamental fish. The genetics are not as simple as 'a single gene', and the breeding program should know what they're doing.
Aug 10, 202511 min read
A serious breeder's home fish room is a system, not a collection of tanks. The minimum hardware setup that supports multiple species, multiple generations, and consistent water quality.
Aug 10, 202510 min read
A serious home fish room needs three things: water that does not vary, water that can be changed in bulk, and water that can be heated and filtered at scale. Here is the minimum hardware to do all three.
Jul 12, 202511 min read
Culling is the part of fish breeding nobody talks about, but it is the operation that determines the long-term quality of a line. Done correctly, it improves the stock. Done poorly, it produces weak fish and ethical problems.
Jun 14, 202510 min read
MAS uses DNA markers to predict a fish's trait expression before it matures, cutting generations from a breeding program. Here is how serious hobbyists apply it to koi, guppies, and discus.
Feb 6, 202512 min read
Most hobbyist breeders stall at F1. Here's how to set measurable selection goals across four generations so each generation actually moves the line forward — not just multiplies it.
