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Q1, How to distinguish between male and female medaka?
To distinguish between male and female medaka, we will focus on both the spine fin and the dorsal fin.
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- Male with a Normal Body Type
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- Female with a Normal Body Type
Q2. Are there breeds that are difficult to distinguish between males and females?
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- Hikari Body Type
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- Male – Hikari Body Type
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- Female – Hikari Body Type
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- Hikari Body Type
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- Daruma Body Type
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- Male of the Daruma Body Type
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- Female with a Daruma Body Type
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- Daruma Body Type
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- Fin Long Breeds (Fin Length, Swallow, Long Fin, Real Long Fin, Wide Fin)
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- Fin-Length Male
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- Fin-Length Female
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- Swallow Male
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- Swallow Scalpel
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- Longfin Male
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- Longfin Female
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- Real Longfin Male
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- Real Longfin Female
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- Male with Wide Fins
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- Wide-Fin
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- Fin Long Breeds (Fin Length, Swallow, Long Fin, Real Long Fin, Wide Fin)
Male and female medaka can be distinguished by their spine and dorsal fins.
The male’s fins are larger than the female’s and are shaped like a parallelogram. In contrast, the female’s fins are smaller and narrower towards the caudal fin.
If it is difficult to differentiate by looking at the spine fin, you can use the dorsal fin as a guide. The male’s dorsal fin has a notch at the base, while the female’s dorsal fin is smooth and not notched.
Let’s begin by examining males and females with normal body types, similar to wild medaka.
- Male with a Normal Body Type
- Normal species males. There is a notch in the dorsal fin, and the fins are almost parallelogram-shaped. Photo Takayasu Oba
<Female with a normal body type>
Females of normal species body type. There is no notch in the dorsal fin, and the fins are almost trapezoidal. Compare it with the male photo above. Photo Takayasu Oba
Are there breeds that are difficult to distinguish between males and females?
Among the improved medaka, there are many breeds with altered body shapes and fins, making it difficult to distinguish between males and females.
However, the sex of all improved medaka can be determined by examining their fins. Remember the characteristics of the spine and dorsal fins mentioned earlier.
You’ll need to get accustomed to distinguishing them based on the variety, so here are some examples.
<Hikari body type>
In the Hikari body type variety, the dorsal fin has the same shape as the spine fin. In other words, the dorsal fin is distinguished in the same way as the spine fin.
< Hikari body type male>
A male of the Hikari body type breed has a dorsal fin with the same shape as the spine fin. In other words, the male’s fins and dorsal fin are shaped like parallelograms.
Photo: Takayasu Oba
<Hikari body type female>
A female of the Hikari body type breed has fins and a dorsal fin that are both shaped similarly (close to trapezoidal). When compared to the male, the difference in the shape of the fins is obvious at a glance.
Photo: Takayasu Oba
< Daruma body type>
This breed has a short body length, and the fins and dorsal fins are also small in proportion to the physique.
However, the shape of the fins remains unchanged, so you can distinguish between males and females by closely examining the size of the fins and the notches in the dorsal fins.
Male of the Daruma body type
A male of the Daruma body type breed has a shortened body, but there is a notch in the dorsal fin, and the fins are wide. The method for distinguishing them is the same as that for a normal medaka.
Photo: Takayasu Oba
Female with a Daruma body type
Females of the Daruma body type breed have the characteristic female traits in both the dorsal fin and the spine fin, though it may be a bit hard to see. Compared to males, each fin appears smaller.
Photo: Takayasu Oba
Fin Long Breeds (Fin Length, Swallow, Long Fin, Real Long Fin, Wide Fin)
This variety has elongated fins. Since it is difficult to distinguish between males and females when the fins are fully extended, it is easier to judge their sex when they are juveniles with a body length of about 1.5 cm, before their fins have grown.
Fin-length Male
Males of fin-length breeds have longer fins, making it difficult to judge males and females by fin size alone. However, looking at the tips of the dorsal and spine fins, the male’s fins are often jagged, while the female’s fins are rounded.
Photo: Takayasu Oba
Fin-length Female
Females of fin-length breeds can be distinguished by comparing them with the male photo above, particularly by observing the tips of the fins.
Photo: Takayasu Oba
Swallow Male
Swallow is a variety with partially extended fins. It’s best to judge males and females in the same way as normal body types by examining the parts of the fins that are not extended, without considering the extended parts.
Photo: Takayasu Oba
Swallow Females
Swallow females are easily distinguishable among varieties with elongated fins.
Photo: Takayasu Oba
Longfin Male
Longfin is a breed characterized solely in males by the elongated strands of the dorsal and spur fins. Females lack these elongated fins, allowing for differentiation between males and females using the same method as with normal body shapes.
Photo: Takayasu Oba
Longfin Female
Females of the Long-fin breed do not differ from females of normal body shape.
Photo: Takayasu Oba
Real Longfin Male
Since the fins of the Real Longfin breed are larger while maintaining the original fin shape, distinguishing between males and females is the same as with the normal body fin. Look for subtle differences, such as the slit in the dorsal fin and the jagged edge at the tip of the fin, to discern between male and female.
Photo: Takayasu Oba
Real long-fin female
In some cases, distinguishing Real Longfin individuals can be very difficult because the fins of females are as large as those of males. It is better to make judgments at the stage of young fish before the fins fully grow.
Photo: Takayasu Oba
Male with wide fins
Wide-fin is a variety characterized by its wide fins. The shape of the dorsal fin also undergoes a change. The photo depicts a male.
Photo: Takayasu Oba
Wide-fin Female
The fins of the Wide-fin variety differ significantly from those of the normal body type medaka, often resembling a “female-like” appearance. This distinction is easier to grasp when compared to males.
Photo: Takayasu Oba
We’ve observed males and females of various breeds, but once you know how to distinguish between normal-sized medaka, the rest is application.
If you’re unsure whether you have a male or female medaka, please refer to this article!
