How to Identify Male & Female Oscar Fish

By Nadine Oraby | 2020 Update

Oscar fish are known worldwide as the monomorphic which clearly states that males and females look exactly identical in terms of their size, shape, and coloration.

So, how to identify male & female Oscar fish? The best method to do that is to observe the breeding tube of Oscars during their breeding period. The male’s tube is smaller and pointed at the end while the female’s tube is larger and rounded at the end.

I wish there was an easy answer for the difference between male and female Oscar fish, but both of the fish look similar. However, there are certain ways we can determine the gender of the fish.

Oscar Fish Male or Female Sex? Sexing Guide (Video)

How to identify male and female Oscar fish?

One of the frequent questions that have been asked is how to tell the difference between a male and female Oscar fish. Unlike other animals, you cannot simply tell the gender by looking at the external features of the fish such as size, shape , and color.

However, there are factors that can be analysed in detail to find the answer to your question. A reliable way to know the gender is to look at the breeding period. Try to observe the pair when they are breeding and their breeding tube as well.

While the male’s tube is smaller and pointed at the end, the female’s tube is larger and rounded at the end. It is obvious that the female Oscar would lay the eggs.

The unfertilized eggs will have a white colour and the fertilized eggs will be yellow. All this is easier said than done. Observing the fish during their breeding time is an arduous task and requires a lot of effort. So, unless you decide on spending some time to observe the fish, you will most likely not be able to find out the genders of your fish.

Breeding is a major factor to determine the gender of Oscar fish

Did you know that Oscar fish are usually bought in pairs because of their friendly and calm nature? Thus, when most people purchase the pair, they want to find out which one is the male and which is the female. Therefore, it is important to identify them during their breeding period by watching specific steps.

Wait for the Oscar fish to mature

It is a major step to wait for the Oscar fish to mature. It truly matures depending upon the tank size and its health. A healthy Oscar would mature at the age of 1 year and would be of 6 to 8 inches in length in a large aquarium.

Place a dark and flat rock

Place a dark and flat rock on the bottom of the tank to lay eggs. The Oscar fish tend to move all the sand and gravel at the bottom and find a spot to lay eggs. The purpose of the rock is to provide a place for them to lay eggs which are easily visible on a dark rock.

Daily inspection of the tank

Inspection of the tank and observation of the Oscar fish should be done daily to get accurate results. The female Oscar fish has a habit of cleaning an area in the tank to lay eggs before they mature.

If you have placed a flat rock according to the previous step and witness the Oscar cleaning that area, then it is obvious that it is a female.

Keep an eye on the rock

Keep a check on the rock on a daily basis to see whether the Oscar fish have laid any eggs or not. If you have kept two Oscar fish in a tank, then you can observe both of the Oscars and see which one spends more time cleaning.

Of course, the one spending so much time cleaning the area is a female Oscar. And if both of them carry out this activity, then both are females.

Check if you have any male Oscar

There are two things to consider to find out the male Oscar fish. The first is that if you are trying to determine the gender of only one Oscar, it will become easier to identify if it is older than two years and it hasn’t laid any eggs.

Secondly, if you have more than one Oscar in the same tank and have witnessed the female laying the eggs, it is evident that the other fish is the male.

Other factors to determine the gender of Oscar fish

The shape, size, behavior, and appearance of the fish can also be used to determine the gender of an Oscar fish. Following are a few methods that can be used to find the gender.

A bump on the forehead

Examine the fish carefully between the eyes and above the mouth. You will notice a bump. If that bump is large and protruding, then it is most likely to be a male Oscar. This bump is known as “nuchal hump” and it is found in many fish such as tilapia, angelfish, Oscar and discus. It is a great indicator of the male fish.

Inspect the bottom of the Oscar

If you suspect it to be a male, you should look at its bottom. If you see a small thorn-like protrusion next to the anus and behind the rear fin, it means that the Oscar fish is a male and if there is a small hole, then it is a female.

Observe the mating season carefully for designs and growth

Male Oscars usually grow bristles, bumps or shiny scales to attract female Oscars during the breeding season. Females also grow these, but their version is smaller whereas the male version tends to be prominent and larger.

Determine the size during the spawning season

During the spawning season, the female fish tend to be bigger in size in comparison to males. You can take a portrait of all the Oscar fish in an aquarium to measure their sizes. Another way is to take out the fish in a net. Put water in it and then measure it with a scale.

Females are larger than the males because they carry eggs in their abdomen. Once the eggs are laid, they will go back to their original size.

Gain all the information you can from an expert

If I am really eager to find out the gender of my fish, then I would definitely go to a fish store or a hatchery and you too can do the same. You can take a picture of the fish along with you and talk to an expert about it.

However, try not to take the fish out of the tank and to a hatchery because they might get stressed out and die. An expert will also give you the relevant information about the breeding period of your male and female Oscar.

Consult online videos, pictures and books

I always search thoroughly on the internet to get all the information I need. Check out the videos on YouTube or different search engines to get additional information to determine the gender of the Oscar.


Differentiation between the male and female Oscar fish can be done by observing the breeding period. It is the most certain factor. However, there are other ways as well.

You can observe their behavior, sizes and appearance. Furthermore, an observation by an expert is a plus point. Consulting an expert is also important as it will help you raise your Oscar the right way.

Related questions

What are the major types of Oscar fish? The most well-known types of Oscar fish are Tiger, Red Oscar, and Albino Oscar. There are other types as well such as the crossbreed which includes Lutino Oscar, Lemon Oscar, and Yellow Oscar. Out of all these, the Tiger Oscar is the most famous Oscar fish.

What is the right time for breeding the Oscar fish? Oscar fish usually matures at the age of 14 months when they are 6 to 10 inches long. However, their sizes are not reliable enough and they may even take a time of 2 to 3 years.

What is the best water temperature that suits the Oscar fish? It is important to take care of certain factors such as the temperature of the water to keep your Oscar healthy in the tank. Make sure that you fill the tank with plenty of fresh and warm water. An Oscar fish’s water temperature should be around 77° F (25° Celsius) to 81° F (25° to 27° C). Thus, It will be beneficial if you get an aquarium heater and thermometer.


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