How to Identify Male & Female Oscar Fish

Oscars are an exciting fish to keep and add excitement in maintaining a dramatic aquarium setting. These are large fish, which can instantly make an impact in the tank. Oscars have a lot of personality, and they can quickly become a hobbyist’s favorite.

But if you wish to breed this fish, determining their sex is the first step.

If you’re wondering how to identify male and female Oscar fish, here’s what you need to know:

Oscars are a type known as monomorphic fish, meaning that both the male and female are the same shape, size, and color. While there are ways you can determine the sex of an Oscar, looking at them and observing their appearance is not one of them. Oscars are identical, and visually determining their gender is impossible.

However, you can do more than a cursory physical examination in the aquarium to identify male and female Oscar fish. Determining their sex takes time and patience. If you have baby Oscar fish, it is impossible to tell their sex. You must wait until they’re at least 12 to 15 months and have grown 4 to 5 inches in length to determine their gender for breeding purposes.

There are many aspects of identifying the sex of Oscar fish. To help you, we’ve compiled all the important information in this article. Keep reading!  

Don’t forget to check out this sexing guide video to determine your Oscar’s sex.

Learning More About Identifying Male Female Oscar Fish

When you’re sexing your Oscars for breeding, part of the fun is watching them interact and pair.

Observing Oscars While They’re Breeding

If you find two Oscars always moving around the tank together, it’s an indication they’ve formed a pair. Now, you must observe them closely. As mentioned earlier, you need to be very patient with the whole process. One of the best ways to determine the sex of your Oscars is to observe them when they lay eggs.

Oscars require a flat rock or surface to lay eggs. When breeding your Oscars, provide them with a flat rock, preferably in a dark color, so that you can see the eggs. Before laying the eggs, the female Oscar will descend to the rock and prepare it for her eggs. You will find her cleaning the surface and swimming around in a circle with her mate. The male will be with her all the time since he will deposit milt once the eggs are laid.

That’s considered an easy way to identify male and female Oscar fish. However, this requires a lot of patience and spending time near the tank observing your Oscar fish.

Identifying Through Sexual Organs

Another way to sex your Oscar fish is to check their sexual organs. While the Oscars are identical in appearance, they obviously have different sexual organs. Once the female fish is an adult, it is hard to miss the egg tube that will protrude around the same area as her anus. On the other hand, the male sexual organ is not so obvious. But when you look, you can easily tell the difference.

The male sexual organ resembles a small spike. The genitals of males and females are near the anus. Both males and females have two holes. One whole is the anus, while the other one is the reproductive organ.

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In females, the reproductive organ is blunter and wider because that’s the tube she uses to release the eggs. To determine through the genitals, you must hold the fish in your hand and look closely. These features are not prominent if you’re watching them swim in the tank.  

Check for Two Females or an Uninterested Male

It is important to remember that a female Oscar fish will lay eggs with or without a male partner. If you have two Oscars in a tank, but there are no obvious breeding signs, you either have two females in the aquarium or a male that’s not interested in pairing up with the female to fertilize the eggs.

As suggested earlier, place a dark stone or surface at the bottom for the Oscars to lay eggs. Unfertilized eggs are white, while the fertilized ones are yellow. If you find unfertilized eggs in your aquarium, you may need to manually sex your fish to ensure you have a pair capable of breeding.

The Venting Procedure

Another way to identify male and female Oscar fish is through a procedure called venting, which means physically examining the fish to determine the sex. As suggested earlier, once you know the difference between Oscar’s male and female genitals, a physical examination is a must.

If you’re a beginner, it is best to seek assistance from professional breeders to help you with this procedure. This is the quickest way to obtain a male and female for breeding without waiting months or trying out various trial-and-error combinations. In case you’re not an experienced fish keeper, please avoid doing this by yourself. Oscars or any other fish can be difficult to handle for physical examination. Without experience, you may end up causing the fish harm.  

The Nuchal Hump

While examining the fish, also look for a bump on the forehead. Male Oscars usually have a large, protruding bump right about the eyes. This bump is called ‘nuchal hump’ and is common in fish such as oscars, discus, angelfish, and tilapia. It is a simple indicator of the male fish.

Oscars Breeding – Everything You’d Need to Know

Now that you’ve acquired the adults and sexed them, you must prepare for the ideal conditions to breed Oscars. Here’s what you need to know.

Providing Adequate Breeding Conditions

Oscars are large fish and need a large aquarium. For a pair, you need at least a 55-gallon aquarium – but the bigger, the better. You will need a separate tank for raising the fry. Prepare the aquarium with potted plants and flat stones or surfaces on the bottom for the fish to lay eggs. Keep the overhead light protected from splashes.

The aquarium should accommodate a filtration system to keep the water clean.

Feeding Your Oscars

Your Oscars need an enriched diet throughout. Feeding them well is also important for inducing the ripening of fish eggs. While pelleted fish food is a staple, the breeding diet should include both invertebrates and whole small fish. The invertebrate portion can consist of edible food shrimp, aquarium snails, and earthworms.

Some breeders may also suggest feeding your Oscars a mix of adult brine shrimp, thawed beef heart, live crickets, live blackworms, trout chow, or freeze-dried euphausiid shrimp.

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Right Water Conditions

Maintaining the right water conditions for breeding Oscars is imperative. Changing water regularly is also important. While the filters will help keep the water clean, you can’t completely rely on them. Best practices are to change 25 to 50 percent of the aquarium water at least once a week to keep the water clean.

The normal water temperature for Oscars should be between 76 to 78 degrees F. But to trigger spawning, the water temperature should be between 82 to 85 degrees F. You may need a large aquarium heater to keep the water adequately warm. Your large Oscar fish can toss the heaters and smash them into the aquarium. Therefore, pick a large, single, solid-state submersible heater with dialed temperature control.

Artificial Incubation

If you have more Oscars that breed in a large aquarium, there is a risk that other fish would eat the eggs and fry. In such cases, artificial incubation is required.

Once the eggs are fertilized, remove the rocks or flat surfaces from the aquarium. Be careful because the Oscars may attack you. Do not keep the eggs out of water for long. Immediately place it in a separate 10-gallon tank with dechlorinated water.

Adding an antimicrobial to the water is advisable. By removing the eggs for artificial incubation, the pair will spawn again in two to six weeks. If you continue to remove and artificially hatch the fry, the Oscar pair will continue to spawn. 

Here are ten things you need to know about Oscar fish before you buy them:

Frequently Asked Questions

How do Oscars have babies?

The female Oscar fish lay in batches of hundreds of eggs at a time. In just a few days, a female Oscar can lay up to 1000 eggs. The male releases the milt to fertilize the eggs. Once fertilized, the Oscar fry will hatch within 72 hours.  

Which Oscar fish should I breed?

When it comes to Oscars, you have many options. The most popular Oscars include the Red Oscar, Tiger Oscar, and Albino Oscar. Some crossbreed variations include Lemon Oscar, Lutino Oscar, and Yellow Oscar. The Tiger Oscar is the most famous of the breed.

What’s the best time to breed Oscar fish?

It takes twelve to fifteen months for Oscars to mature. During this time, your Oscar will grow six to ten inches long, which is usually when professional breeders start breeding them. In some cases, it can take up to two years to mature and be ready to breed.

Do Oscars eat their eggs?

Yes, Oscar fish consume their eggs. Once the eggs are laid and fertilized, it is best to remove the parents to another aquarium to eliminate the risk of being eaten by the parents.

Do Oscars breed with other cichlids?

Oscars do not generally get along well with other cichlids.


To conclude, distinguishing between male and female Oscar fish can be an engaging and rewarding part of fishkeeping. By observing their behavior, fin shapes, and even breeding habits, you can become an Oscar expert in no time. So, dive into this fascinating world of aquatic life, and get to know your Oscar fish on a whole new level.

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Nadine Oraby

My name is Nadine; I am a passionate writer and a pet lover. People usually call me by the nickname “Joy” because they think that I am a positive and joyful person who is a child at heart. My love for animals triggered me to create this blog. Articles are written by vets, pet experts, and me. Thanks for visiting. Your friend, Nadine!

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