Josui Medaka (如水メダカ)

A graceful blend of Swallow fins and Morpho brilliance

Overview

The Josui Medaka (如水メダカ) is a captivating ornamental strain that brings together the elegant Swallow fin trait and the luminous Morpho blue iridescence. As it swims, the extended, glimmering fins ripple like silk in water — a truly mesmerizing display of form and color.

Breeder and Release

• Breeder: MEDAKA NO YAKATA
• Released: October 2023

This variety was created through careful crossbreeding between a Black Morpho Hikari-type (MLFH × BMA line) and Ryū no Tategami (a Blue Miyuki Swallow Hikari-type). The goal: to isolate and stabilize the Morpho glow in a Swallow fin body.

• In the F1 generation, individuals showing strong Morpho-like fin glow were selected.
• In the F2 generation, Swallow-type individuals emerged in both blue and black body colors.
  • The blue-bodied line was named Josui.
  • The black-bodied line was named Kanbee (not yet released).

The name Josui was inspired by Kuroda Josui, a famous samurai from Fukuoka Prefecture — the birthplace of the original Morpho strain.

Key Features

• Swallow Fin Structure:
  Irregularly extended fin rays, unique to each fish, creating a dynamic and soft flowing appearance
• Blue Morpho Glow:
  Iridescent blue shine within the fins — a signature of the Morpho line
• Natural Variation:
  Each fish has different fin thickness and length — ideal for breeders focused on line selection
• Pure Swallow Lineage:
  No long-fin traits are mixed in; only true Swallow-type expression
• Balanced Hikari Body:
  Emphasis on symmetry and clean form, with properly shaped caudal and paired fins

Fixation Rate

By the F4 generation, Josui has achieved a fixation rate of over 50% for the ideal combination of Morpho shine and Swallow fin traits — making it not only beautiful but also stable in breeding.

Conclusion

The Josui Medaka is a beautiful harmony of structure and glow — a rare and refined variety that speaks to the elegance possible through medaka breeding. With its graceful movement and glittering fins, Josui is an ideal choice for collectors who appreciate medaka with depth, history, and uniqueness.

Image and translation courtesy of: https://medakazukan.net/post_lp/%e5%a6%82%e6%b0%b4/