How Do You Tell If Fish Are Male Or Female? | Aquascape Addiction

How Do You Tell If Fish Are Male Or Female?

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We cover the 7 main ways to find out if your fish is male or female, it can vary slightly depend on the type of fish but these 7 points should give you the answer in most cases.

How Do You Tell If Fish Are Male Or Female?

If you have fish in your home aquarium, you might not know what gender they are, male or female. For some people this simply is not important, but for others it is. Your fish may be fighting, which could be because you have two males. Your fish might all of a sudden turn into many fish because fish of the opposite sex have bred.

Or maybe you have been trying to breed fish but it just is not working. The point is that you need to be able to tell what gender your fish are for many different reasons.

7 Ways To Tell If Fish Are Male OR Female

So, how do you tell if fish are male or female? Keep in mind that the sexing methods talked about below do not apply to all fish, but a combination of them can be used to effectively determine the sex of your fish.

1. The Nuchal Hump

First of all, if you want to determine the gender of a fish, try to see if it has a nuchal hump. This is a bump that often grows on the foreheads of many male fish. If your fish has one of these big humps on its head, almost like a swollen bump from being hit, you can take it as a solid sign that the fish is a male.

When it comes to cichlid fish such as tilapia, Oscars, angelfish, and discus fish, the presence of a nuchal hump is a clear indication of being a male. Keep in mind that many fish do not grow these humps whether make or female.

2. The Anal Fin

There are many fish out there, which when they are male will have a larger anal fin. Many male fish have larger anal fins than their female counterparts.

Once again, this method does not work for all fish, mainly because there are only a few species of fish which have this specific anal fin, ones such as the Poeciliidae family of fish.

You can use the anal fin method on fish such as mollies, swordtails, guppies, wags, and platies too.

3. The Dorsal Fin

Another fin that you can look at to tell whether a fish is a male or female is the dorsal fin. Just like with the anal fins, males will often have larger dorsal fins than their female counterparts.

If you have 2 fish, one of which has a much larger dorsal fin, the one with the smaller fin is definitely the female. This method works really well for many different types of cichlids including discus fish, tilapia, Oscars, and angelfish.

4. Bumps & Growths

When it comes to mating season, many male fish will develop these little bumps all over them. The majority of these bumps will usually be concentrated to the pectoral fins, near the gills, and on the forehead.

These little bumps have something to do with mating, making a male’s presence known, and a way to try and get a female’s attention. When breeding season is over, these little bumps will disappear.

This is a good method to determine the gender of goldfish and other such fish. When it comes to male pleco fish, when breeding season comes along, they will grow long whiskers like bristles along their pectoral fins and around the mouth. In general, seasonal flashy growths during breeding season are an indication that a fish is male.

5. Size

With many fish species, the females can be substantially larger than the males. Therefore, if you have two fish of the same kind, if one is a lot bigger than the other, chances are that the smaller one is the male. This may not necessarily be true in terms of length, but more so in terms of width and girth.

This is not true for all fish, but for Koi and many goldfish species it certainly is. Keep in mind that the reason for this does also have to do with breeding season. Female fish can carry hundreds of eggs inside of them, something which will obviously contribute to the size of it.

6. Behavior

Another good way in which you can tell if the fish you have is male or female is to observe their behavior. You do have to be careful here because some species of fish are more docile while others are more aggressive.

However, generally speaking, you can be sure that the more aggressive and territorial fish are the males. This is just like with humans where males are the big loud ones and females are the quiet thinkers. You can’t always rely on behavior because it can depend on other circumstances, but it is a good indicator.

7. Research

One of the first things that we would recommend doing is some research on the specific fish you have. Like we have already said, each species of fish will have different characteristics you can observe to tell if they are male or female.

Your best bet is to bust out Google and research the fish in question. This should tell you exactly what you need to know in order to determine the gender of your fish. Googling this or watching some good old YouTube video will definitely help.

Finally, if you still can’t come to a solid conclusion, you can always try bringing your fish to a vet or some other kind of expert to have them give you a helping hand.


The bottom line is that some fish are harder to determine what sex they are than others. However, most, if not all, have specific traits that only the males or females exhibit. So, you should probably go do some research on your specific fish and go from there.