how to tell if an angelfish is a boy or girl

How To Tell The Difference in Male And Female Angelfish

Learning how to sex angelfish can be tricky. For saltwater species, the differences between males and females are subtle. For freshwater variants, it’s nearly impossible, since these angelfish have very little sexual dimorphism. Even experienced fish keepers can find it difficult, but there are ways to identify the difference. Observing spawning behavior is the most accurate method.

Female angelfish are usually slightly smaller than their male counterparts. They will have smooth front fins, a lower dorsal fin, and a tube-like papilla. Males are rounder in shape, with more erect dorsal fins, forked front fins, and a triangular papilla. Males will also have a noticeable bump on the forehead. In marine angelfish, females may also be duller in coloration and have reduced patterns, if at all.

These differences do not appear until the fish have matured. It is virtually impossible to sex juvenile angelfish. Physical differences aside, the most effective means of sexing an angelfish is allowing them to mature. They will pair off into breeding pairs or harems. This will reveal their spawning behavior and the shape of the individual papilla.

How To Determine Male And Female Angelfish

Angelfish come in two main categories, each with their own signs of gender. These include:

  • Saltwater angelfish (marine angelfish). These come from the ocean waters in the southern hemisphere.
  • Freshwater angelfish. As the most popular type to keep in aquariums, these fish originate from rivers throughout South America.

There are over 100 species of angelfish on the planet – some marine, some freshwater. Most share common traits in their appearance and aggression levels. However, all of these species display little sexual dimorphism. That’s the technical term for visual differences between male and female fish.

In general, males and females look almost completely identical. No matter the type, it’s impossible to tell males from females prior to maturity. You will have to wait between 5-7 months from hatching before even attempting to sex an angelfish.

Determining The Sex Of Marine Angelfish

Sexing a marine angelfish will be slightly easier. Once they’ve reached maturity:

  • The size differences will be more prominent
  • The coloring and patterns may be duller in females

However, this is usually only helpful to experienced aquarists. You will need to know your particular species well. When you’re familiar with the average sizes and colors for a male or female, you can make an educated guess.

However, this information can still be muddled. Unless you have a male and female side-by-side to compare, the differences will be very slight.

how to tell male and female angelfish apart

Male Vs. Female Freshwater Angelfish

Freshwater angelfish are the most popular type to keep in home aquariums. As such, it’s ironic that these are the most difficult fish to sex. Males and females will be nearly the same in:

  • Size
  • Coloring
  • Behavior outside of mating season

Certain types will have more differences than others. If the species in your aquarium shows no physical differences, you’ll have to wait until they start mating. This should give you one or two clues to follow.

How To Tell Male And Female Angelfish Apart

For the best sexing results, you need multiple angelfish to compare. Ideally, you will have 6 or more angelfish in a single tank. Of course, this aquarium must be large enough to properly house them. Otherwise, the fish may:

  • Begin fighting out of fear and constraints, rather than sex-specific aggression
  • Lack of exercise and food. This can impact their growth and make all your fish smaller or larger than their sex-specific size
  • Have trouble pairing up. With their space and food shortage, they’ll worry about surviving more than mating.
  • Lose coloring. Angelfish that are malnourished or stressed will become dull in color with fewer stripes. This can muddle your gendering tests.

If the tank conditions are perfect, you can then use each angelfish as a comparison for another. You should look for:

  • The size of their belly
  • Their markings and patterns
  • The intensity of their coloring
  • Their aggression levels
  • Any bumps on their head
  • The shape of their dorsal fin
  • Any forks in their ventral fins

These will be their main visual indicators. If you can’t tell any difference, then look a bit closer. It may not give you a firm answer, but it will better inform your guesses.


Males are often more colorful and patterned than female angelfish. In contrast, females bear duller coloring and reduced patterns. It is more common to see drastic dimorphism in marine angelfish than freshwater angelfish.

Bodies And Bumps

Across all angelfish species, males will usually have a larger body and a notable bump on the forehead. Occasionally, this latter feature appears before maturity. Female angelfish will have a smoothly sloped dome without a bump.


In certain angelfish species, the dorsal fin may be more upright in females. It may slope down in males.

Male freshwater angelfish have ventral fins that are forked. Females do not. Keep in mind that this isn’t true for all species. Your type of angelfish may have no forks at all, regardless of its gender.


Between these fins and the anal fin is the papilla. Male angelfish will have a thin, pointed vent. Meanwhile, females have a thin, tube-like vent with a rounded tip.

These are not always visible, and may only appear when males and females are grouped together. The traits become more prominent during the breeding season.

Belly Size

Take a long gander when the fish is looking directly at you. Female fish will sometimes have a rounder belly to accommodate the eggs they carry.

How To Tell If An Angelfish Is A Boy Or Girl

However, there are cases where all the physical traits are the same for every fish in your tank. Perhaps:

  • You’ve managed to purchase several fish of one gender
  • You own a species that shows no physical differences
  • Your fish have not properly developed yet

If that’s true, you’ll need more thorough examinations. Here are more accurate ways to parse the males from the females.

Waiting For Matured Fish To Pair Off

Angelfish typically pair off into male-female pairs at maturity. A close observation should reveal angelfish separating into these pairs. The pairs may kiss, which is a popular trait in the species and signifies courting behavior. You can then be sure that one is male and the other female.

This method is only used for freshwater angelfish. Marine angelfish will group into harems of 1 male and multiple females instead of 1-1 pairs. As marine angelfish are quite territorial, it isn’t advised to have more than one in each aquarium. That is, unless it is a species that mates for life.

If you own freshwater angelfish, then a pair is a useful clue. By knowing that one is male and the other is female, you can tell them apart by their spawning behavior.

Observing Spawning Behavior

Angelfish are not live bearers, meaning that they reproduce through spawning. A female angelfish will lay her eggs directly onto a suitable surface using her tube-like vent. A male fish will then release sperm in a cloud over the eggs.

During spawning, the papilla of the fish will also be visible. However, it can be difficult to clearly see the organs on smaller angelfish species. Instead, it’s best to observe which fish lays the eggs.

Sadly, this does rely on being in the right place at the right time. Both male and female angelfish will take turns fanning the fertilized eggs to keep them oxygenated.

This method does require you to cohabitate multiple angelfish in the aquarium. If you are specifically trying to create single-sex aquariums to prevent breeding, this isn’t an ideal method. The eggs can be removed if necessary, but fry will hatch within days of the eggs being fertilized.

Are Male Angelfish Bigger Than Females?

The size of an angelfish will mostly depend on:

  • Its species
  • The amount of food it eats

However, if the conditions are ideal, the males may be larger than the females. These differences are usually slight, relying more on the shape of the body than the size.  

  • Males tend to be more circular
  • Females are more angular

Do Male Angelfish Grow Faster Than Females?

Male angelfish also tend to grow slightly faster than females. That’s helpful when you know all the angelfish in your tank are the same age. You can look at which have grown more quickly and identify them as males.

However, some fish will be more territorial and claim more food. This can help it grow in size more rapidly. That will muddle any educated guesses at the creature’s sex.

determining the sex of angelfish

Are Male Angelfish More Aggressive Than Females?

Males are generally more aggressive than females. In freshwater angelfish, males often attack rivals and more vigorously defend their territory. This is designed to impress female angelfish into choosing them as mates.

Marine angelfish are even more prone to this. Males will chase other males away from their harems.

However, this information isn’t a great benchmark. That’s especially true during mating season. Females may grow just as aggressive and defensive of their:

  • Mates
  • Fry
  • Territory

That’s because freshwater angelfish need a lot of space. Aquariums that lack space or are too crowded will see aggressive behavior. Likewise, angelfish that pair for life share the responsibility of their children.

Males and females can show the same amount of aggression over their eggs and fry. You can’t tell which one is the mother just because of its protective habits.

Can Angelfish Change Gender?

Certain kinds of fish are able to change gender. If your supposedly male fish starts mating like a female, you may conclude it that simply changed its sex. This can be both true and false.

Marine angelfish can change from female to male. It’s rare to see this happen the other way around. Additionally, it’s only possible in certain species of marine angelfish.

Meanwhile, freshwater angelfish cannot change their sex at all. No matter the situation, these fish are stuck with their birth gender. If your fish starts manifesting signs of a different gender, then it hasn’t tapped into a biological trick. Your guess was simply incorrect.

How Do Angelfish Change Sex?

Sequential hermaphroditism is when animals spontaneously change from male to female or female to male. This is usually due to social or environmental factors. Zoological Science notes that this phenomenon is common in reef fish species. That’s especially true for haremic social structures, which marine angelfish have.

Researchers discovered that the marine angelfish, Centropyge ferrugata, was capable of changing sex. Copeia notes four other species of marine angelfish that have presented protogynous hermaphroditism as well. These fish change on a physical and physiological level, adopting traits of the opposite sex, like:

  • Organs
  • Reproductive abilities
  • Physical appearance
  • Behaviors

Most commonly, marine angelfish experience protogynous hermaphroditism. This is a female-to-male change. It’s very rare for males to transform into females. Despite being in the same family, freshwater angelfish lack this trait. They cannot change their sex, even if it would help them environmentally or socially.

Do You Need To Sex Angelfish?

It’s important to sex your angelfish if you intend on:

  • Breeding the fish
  • Preventing any breeding habits

This will allow you to pair them or separate them as needed. However, if you’re struggling to tell the gender of your angelfish, you can wait until they’ve started to form pairs. At this stage, you can separate one from the other:

  • In different tanks
  • With a divider in one tank

This will prevent breeding. The care and treatment of each fish will not change based on its gender. You can keep multiple angelfish without ever knowing their sexes. So long as you’re prepared to remove the eggs as they appear, your fish can live in harmony.