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You don’t need to have intentions of breeding goldfish to be curious about the sex (or gender) of your goldfish. Knowing it can help you understand behaviors your fish exhibit. For example, an adult male chasing a female around the tank and nipping at her is sometimes considered breeding behavior, while a female chasing a male around the tank and nipping at him is likely bullying.
To help you better understand and care for your fish, here are the things you should know about sexing goldfish. Maybe today will be the day you discover that Patrick the goldfish is actually Patricia!
The term gender is often used interchangeably with sex for animals in informal settings or speech. However, the correct technical term for telling whether an animal is male or female is sex, not gender.
Is There a Trick to Successfully Sexing Goldfish?
There are a few key points that you should know when attempting to determine your goldfish’s sex. The first is that goldfish are not sexually dimorphic until they are adults. This means that when your goldfish is a juvenile, you will not be able to accurately determine the sex. Sexual dimorphism refers to physical differences between sexes, and even though goldfish become sexually dimorphic with age, the differences are minute.
If you didn’t raise your goldfish from eggs, it may be difficult to determine their age. Goldfish reach sexual maturity between 9 and 12 months of age. Most goldfish in the feeder tanks at the pet store are 2–3 months old, but you won’t know for sure until your goldfish actually reaches sexual maturity.
The second big thing to know about sexing goldfish is that the easiest time to try to solve this puzzle is to wait until breeding season. In the wild and in ponds, goldfish will become ready for breeding after the water begins to warm and they come out of torpor. In tanks, your goldfish would only try to breed if you simulated a winter and then simulated a spring (by constantly controlling and modifying their water temperature and light exposure).
A final factor to keep in mind is that although your fish’s body shape can sometimes be a useful clue to determine their sex (especially during the breeding season), this trait can be heavily modified with selective breeding, so identifying factors that work on one spawn or type of goldfish may not work on another. It also means you cannot use the same criteria of body shape and/or size to try to sex two different types of goldfish.
For example, let’s say that you have two fancy goldfish, a ranchu and an oranda (also known as a “red cap”). You cannot compare the body morphology of your ranchu goldfish with that of your oranda to determine their respective sex. Although different types of fancy goldfish are often housed together, their body morphologies are quite different and unique to each strain.
The 5 Tips on How to Sex a Goldfish
1. Watch for Breeding Behavior
Breeding behavior in goldfish is very distinct and makes it easy to determine who’s male and who’s female. Male goldfish will chase a female goldfish and nip at her back end in an attempt to stimulate her to release eggs. You may see multiple males chasing one female. This behavior can result in injury to the female as she attempts to escape the males, but it usually does not involve the males themselves damaging her fins.
Although this sounds straightforward in theory, it’s more difficult in practice and cannot be used as the sole way to determine your fish’s sex. There are a few reasons that this is the case.
- This behavior only presents itself in healthy adult goldfish that are exposed to the seasonal shift of winter into spring (either naturally in a pond or in aquariums where the lighting and temperature are controlled to simulate these changes). It will never happen in the vast majority of indoor aquarium setups.
- In the absence of a female, an all-male group of goldfish will just chase each other around in the breeding season, which can lead to an incorrect sexing of your fish.
Since this behavior alone isn’t enough to sex goldfish, you need to look for other cues.
2. Check the Vent
Goldfish anatomy differs from mammal anatomy in many ways, including that goldfish do not have the same external excretory and sexual organs that mammals do. They have a vent, which is a body opening that releases waste and genetic material, be it eggs or sperm.
During the breeding season, female goldfish tend to have a slightly out-turned (convex) vent, while males tend to have a flat or inward-turned (concave) vent. So, if you view your goldfish in profile, a female will have a small bump where the vent is located, and a male will not. Do keep in mind that this difference only presents itself during the breeding season and is only displayed in healthy adult goldfish.
3. Look For Tubercles
During the breeding season, male goldfish develop small white spots, called tubercles, that are concentrated on their gill coverings and the base of their pectoral fins. These flecks are often confused with ich because of their salt crystal appearance. However, tubercles are concentrated on the gill plates and pectoral fins, while ich indiscriminately covers the body. Female goldfish do not develop tubercles.
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4. Check the Body Shape
When females are ready to spawn, they will begin to develop a more rounded abdomen as they produce eggs. Male goldfish will not have changes in their body shape when they’re ready to breed, so a goldfish that is slightly rounder and larger than usual during the breeding season is likely a female that is ready to spawn.
5. Look For Spawning
If you witness your goldfish spawning, you’ll easily be able to determine the sexes. Female goldfish will release large quantities of yellow to orange eggs, and the males will follow along behind her to fertilize them. Females may begin releasing eggs while still attempting to escape from the males, so you may spot eggs in various locations in your tank.
Fertilization of these eggs happens externally, so there’s no way to catch your fish “doing the deed” during the breeding season. Be warned that goldfish will indiscriminately eat their own eggs and young and have no parental instincts whatsoever. They should be removed from the spawning tank once they’ve laid their eggs.
Final Thoughts
Determining the sex of your goldfish is not an easy task! Goldfish are busy fish and always seem to have somewhere to be. Getting them to hold still long enough for you to get a good look at things like vent and body shape can be exceptionally difficult. Methods like watching for behavioral changes and spawning are far more reliable, but if you are not interested in goldfish fry potentially happening, you may want to try to determine the sex before spawning begins to take place so you can identify your males and females.
Expecting breeders to determine the sex of your goldfish at the time of purchase is unreliable, and expecting the people at big box pet stores to be able to tell the difference is even more unreliable since they are less specialized than goldfish breeders. Understanding some of the sexual dimorphisms between male and female goldfish can make it much easier for you to determine the sex of your goldfish during the breeding season.
Related Reads:
- How Long Do Goldfish Live? Average Lifespan, Data & Care Guide
- 12 Oldest Goldfish That Ever Lived (With Pictures)
Featured Image Credit: Hans Braxmeier, Pixabay
