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How To Tell If Goldfish Is Male Or Female?

There are so many reasons why you want to know how to tell if goldfish is male or female; it could be you want to find out your goldfish gender to name them or for breeding purposes or not to breed in order not to over-populate your tank or you simply wish to learn to distinguish your goldfish genders.


Whatever your reasons are, there are ways to identify your goldfish gender by physically looking at it. However, all these methods work with your juvenile goldfish; to apply all the techniques in determining your goldfish sex is possible only with sexually matured specimens.


With having said that, you would want to know when your goldfish reaches its sexual maturity? It is around a year or so, give or take a couple of months. However, there is no way for you to know your goldfish’s age when you buy it from your pet store unless you examine their scale for the rings with a microscope!


Body shapes

Identifying the gender by looking at the shape of their body is one of the standard techniques adapted along with other techniques.

Female goldfish tend to have a rounder and deeper body whereas, males tend to have slimmer and longer bodies of the same age.

Females look shorter and rounder in their belly area when compared to male goldfish.

During the breeding season, the females start to develop a roe of bulge on the one side as the eggs develop, making it look lopsided or asymmetrical.

The shape of the vent

The vent is the part from where the goldfish release their waste and the eggs and milt. It is located beneath the anal fins, which are right below the tail fins. Also, their fins are shorter and thicker.

Females have a rounder and protruding vent; the protrusion is in white when closer to the spawning. The vent appears as a raised surface on their abdomen when viewed from the side.

Furthermore, the females protruding vent may even slightly appear thicker than the males.

NOTE:  remember overly rounder belly could be a sign of Dropsy or constipation; if the scales stand out, it is most probably Dropsy. Treat her accordingly. If after the treatment it still doesn’t improve, it could be a stone or a tumor. By any means, you suspect your goldfish has cancer; it’s best to euthanize as she must be suffering.

Surprisingly, sometimes an unusual rounder belly means egg-bound; the fish might produce eggs excessively and build them up, causing the abdomen to bulge.

Male goldfish have long and slender body shapes like a streamline. And also, in general, the male’s vent is oval, tapered, and elongated. It caves in rather than protruding.

Midline ridge

This midline ridge appears at the underbelly of your goldfish. It extends from the back of the pelvic fins to the vent; it is raised running line appears on the underbelly of males; in females, this line is indistinct.

Look for Tubercles

One of the most giveaway signs of male goldfish is the development of tubercles on their gill plates. Look for tiny white spots on the gill shield called “breeding tubercles” or “breeding stars.” It can also appear on the front pectoral fins, heads, and even on the body scales.

They are a bit coarse to the touch and appear tiny freckles of salt; it is testosterone and keratin-based.

Most people confuse it for white spot disease or Ich. The breeding stars make a beautiful pattern according to the scales’ shape, which takes the alphabet “C” shape; Ich or white spot disease will have randomly scattered white spots on the fish body; they won’t have any regular pattern or shape and are usually more prominent freckles than the breeding stars.

Typically, tubercles appear only during the breeding season; however, some matured old goldfish have tubercles through the year.

The absence of tubercles doesn’t mean it is a female goldfish; sometimes, the male members may not always exhibit tubercles.

The Purpose of Tubercles:

  • They use them to stimulate breeding females
  • To defend their spawning territory.

Shape and the Length of the fins


The females have shorter and thicker fins, while the males tend to have longer and thinner fins.

You can apply this technique to common goldfish and other short-tailed fish; however, with longtailed goldfish such as Veiltail, or fantail you won’t be able to use this technique.

Pre-spawning Behavior

Pre-spawning or mating behavior is the most apparent technique to distinguish male to female goldfish.

The female will have a sudden interest in a particular spot, most probably live or fake aquarium plants, green in color; they swim and forage around it more frequently.

Males will be the chasers, following the female underneath or behind jabbing and butting; the females are on the run, constantly.

However, do not confuse bullying and aggression for spawning behavior. Although goldfish is a peaceful species, some member can be bully even as a juvenile; for them its a game to chase each other, which usually lasts for few seconds or maximum a couple of minutes.

If this chasing lasts longer than a couple of minutes, then it’s a sign of aggression. You would want to address it right then and there.


How to tell if goldfish is male or female – Wrap up:

How to tell if goldfish are male or female is not challenging when they are sexually matured. As we have seen, there are apparent physical differences from male to female goldfish; especially during the spawning season, the tell-tale signs are unmistakable.

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