I have a bit of problem in my pond at present, I have too many fish and am going to have to give some away in due course. But the question is, how to tell what is male and female, as currently my fish breed very successfully every year. As good as it is to have this problem, if I can’t get the balance right, I’ll soon be back to the same situation I’m in. Therefore, I’ve put together this guide to try and help people in a similar position to me.
None of this however is wonderfully easy, one article I read on the topic described it as notoriously difficult, and personally I’m inclined to agree.
Look for Breeding Tubercles (The “Stars”)
This is the most reliable physical sign for males, this is much easier to spot if your goldfish are in a tank rather than in a pond, but still works regardless. During breeding season, males develop tiny, white, sand-like bumps called tubercles or “breeding stars.”
- Where to look: On the gill covers (operculum) and also on the leading edges of the pectoral fins (the front side fins).
- Note: These are often mistaken for “Ich” (White Spot Disease). However, Ich spots are random and look like salt sprinkled over the whole body, whereas tubercles will always appear in neat and symmetrical patterns.
Examine the Vent (Anal Opening)
The vent is located just in front of the anal fin on the underside of the fish. This is often referred to as the “Innie vs. Outie” method.
- Females: Will usually have a rounder, protruding vent (an “outie”). As they fill with eggs, this becomes more prominent.
- Males: Have a smaller, narrower, and concave vent (an “innie”).
Body Shape and Fins
- Females: Generally have a rounder, thicker, and deeper body. If you look at them from above, they may appear well to be asymmetrical or “lopsided” if they are in the process of carrying eggs.
- Males: As a rule these tend to be more a streamlined, thinner, and longer shape. Their pectoral fins are often slightly longer and more pointed than the shorter, rounder fins that are found on females.
- The Midline Ridge: Many males will have a visible “seam” or raised ridge running along their belly from the pelvic fins to the vent. Females usually have a smooth, round belly.
Observe Breeding Behavior
If you see one fish relentlessly “harassing” another, then you are likely witnessing a mating chase in progress.
- The Male: Will be the pursuer in the chase. He will actively chase the female around the tank or your pond, nudging her belly and flanks tin an attempt to encourage her to release the eggs she is carrying.
- The Female: Will be the one being chased. She will often be pushed into plants or the sides of the aquarium as part of the process.
| Feature | Male | Female |
| Tubercles | Present (gills/fins) | Usually absent |
| Vent Shape | Concave (Innie) | Protruding (Outie) |
| Body Shape | Streamlined / Thin | Round / Deep / Plump |
| Behavior | Chaser | Being chased |
Hopefully you have found this short guide helpful. There are also plenty of videos available which will help you with your quest to identify which of your fish are male and female. If you have any other good tips for this which you think we have missed, please do drop us a message we would love to hear from you
