How to Tell If a Goldfish Is Male or Female — Complete Guide for Hobbyists

Wondering how to tell if your Goldfish is male or female? You’re not alone — sexing Goldfish can be one of the trickiest parts of fishkeeping, especially when they’re young or not in breeding condition.

The good news? By looking for a combination of physical features, behaviour, and subtle seasonal changes, you can usually make a pretty accurate guess. In this guide, I’ll walk you through the top signs to tell male vs female Goldfish, plus share a few personal tips I’ve learned over the years.

Breeding Stars (Tubercles)

One of the most well-known male Goldfish breeding signs is the appearance of breeding stars (also called tubercles). These are small white dots that usually develop during the breeding season.

• First appearance: On the front ray of the pectoral fins. Males also usually have a thicker first ray in this fin, which often ends in a more pointed shape, while females tend to have pectoral fins with a rounder appearance overall.

• Spread: As hormone levels rise, they may appear on the gill plates and, in some cases, on the pelvic fins or even the sides of the body.

⚠ But beware:

• Some females, especially in more “aggressive” goldfish breeds like Ryukin or Black Moor/Demekin, can also develop breeding stars.

• In humans, higher testosterone in women can cause male-like traits (deeper voice, more muscle mass). I believe Goldfish may experience something similar hormonally.

No Stars? Still Possible

Not all male Goldfish grow visible breeding stars, yet they can still breed perfectly well. Sometimes the dots are so tiny you need to view them from the side under bright light.This can also occur in females, so it’s best to combine this with other methods before deciding.

Male Ranchu Pectoral Fin (notice the fin has no breeding stars despite being confirmed male)

Female Ranchu Pectoral Fin (notice how the fin has some bumps which could be misidentified as breeding stars)

Goldfish Vent Shape

Examining the vent or cloaca (the opening on the underside of the fish) is another common sexing Goldfish method:

• Male: Smaller, more slit-like vent.

  

  Male Metallic Ranchu Vent (notice is in narrow V shape)

• Female: Rounder vent with a slight protrusion, like an “outie” belly button.

  

  Female Metallic Ranchu Vent (notice the round protusion, size and round shape)

The challenge is that both sexes can vary greatly, so it takes a trained eye to be certain.

Top-Down Body Shape

Looking at your goldfish from above can also give clues:

• Female goldfish (especially fatter fancy varieties) often look asymmetrical, with one side of the body bulging more.

• Males tend to look slimmer and more streamlined.
  

  

  Male Mettalic Ranchu (left) Female Mettalic Ranchu (right) you can see the females left side is slightly larger

  
  

Growth Rate Clues

Males often grow slower than females — but be cautious. Genetics and water conditions can also affect growth. This method works best when comparing siblings raised together under the same conditions.

Feeling for an Egg Cavity

If you’re confident handling your fish:

• Gently press under the vent (similar to hand-spawning but much lighter).

• Female: Area feels softer.

• Male: Feels firm, sometimes with a ridge.

Some long-bodied females may also have a ridge, so it’s not 100% foolproof.

Colour Intensity

Male goldfish often display more vibrant colours than females. While this isn’t a primary sexing method, it can be a small clue when combined with other observations.

Rearing Temperature & Sex Ratio

If you’ve bred the fish yourself, the temperature they were raised at can influence the ratio of males to females. Higher temperatures may result in more males, sometimes creating “neo-males” — fish that are genetically female but hormonally male.

The Most Reliable Method — Spawning

At the end of the day, the only 100% reliable way to tell if a goldfish is male or female is to see them spawn:

• Female: Releases eggs.

• Male: Releases milt (fish sperm).

Until then, use a combination of the above signs to get the best guess.

Thank you for taking the time to delve into this post. We'd be thrilled to hear about your experiences with Goldfish breeding. What challenges have you encountered, and what successes have brought joy to your aquatic endeavours? Your insights enrich our community, so please feel free to share your thoughts.