What kind of fish is Nemo?

In this post, we will answer the question “What type of fish is Nemo?”.

We will also understand more about Nemo biology and ecology.  

What kind of fish is Nemo?

Nemo is an Amphiprion ocellaris. It is a marine fish species that belongs to the Amphipriongenus. These fish are known as Common Clownfish or Ocellaris Clownfish. Their main characteristic is the bright orange colouration of their body. Over these tones, several white stripes stand out, demarcated by thin black lines. 

The Clownfish

Altogether, there are about 30 different clownfish species in this genus. They can be yellow, orange, red and black, with most having whitish streaks or bars.

The biggest clownfish ever recorded was a being 18 centimetres long. The smallest measured around 10 centimetres in length.

Using anemones as a refuge, this animal can eliminate the anemones parasites found and defend the host from its main predator, the butterflyfish.

The anemonefish, as it is also known, is born with immature male and female sexual organs. Therefore, they can change gender when needed. This animal has a hierarchical social relationship. The group is led by the largest of the females, followed by a breeding male, second in size within the group.

These species are responsible for around 40% of the world trade in marine ornamentals and aquariums. They are either bred in captivity or captured from the wild. They are very popular, not only because of their colours, of course, but also because they are very active and gentle animals, and lives very well with other species.

Life Stages

The unfertilized egg is semi-transparent and the yolk takes a great part of its space.

Embryonic period

When the egg is fertilized, the embryo is covered with a smooth, transparent chorion. The embryo measure between 1.5 and 3 millimetres in length and 0.8 to 1.84 millimetres in width.

This step is characterized by the yolk being fed endogenously. Furthermore, to identify levels of development, this period is divided into three phases: excision, embryonic and embryonic eleuthero. 


Egg incubation usually occurs after sunset, peaking during hours of complete darkness.

The embryo starts to tremor the moment it starts to execute a vigorous wave movement, in which the body and the caudal area move rhythmically. Thanks to this, the egg capsule is breaks and the embryo’s tail emerge first. 

Larval period

The larval stage begins with the transition of the larva nutrition to external resources and is completed with the total ossification of the axial skeleton.

Another feature of this phase is the persistence of some embryonic organs, which will be permanently replaced by others or may disappear if the structure is not functional. 

Youth period

This period begins when the fins are completely differentiated and the vast majority of temporal organs are replaced by definitive organs. The stage culminates when gamete maturation begins.

The transition from larva to fish involves significant changes. Therefore, some organs and structures develop during the juvenile stage.

The young ones are no longer pelagic feeders to be epibenthic. That is when they begin to eat shrimp, mussels, and fish. 

Sub-adult period

This period starts with the first stage of gamete maturation and is characterized by very rapid growth. At this stage, the youngsters show aggression towards their subordinates, concerning the territory and spawning area. 

Adult period

The main factor that identifies adulthood is the maturation of the gametes, which allows reproduction. In females, the first spawning (laying) occurs when they measure 70 to 80 millimetres, about 18 months after hatching. The male matures when it reaches a length of 58 to 65 millimetres. 

Senescent period

When clownfish age, egg production, spawning frequency, and growth rate decrease. Regarding egg-laying and growth, they stopped after 6 to 7 years after the first spawning.

General characteristics


The colour of clownfish varies with species. The base shade can be reddish-brown, bright orange, black, yellow, or pinkish brown. A particular feature of this genus is the vertical stripes that cross the fish body. These can be one, two, or three. These stripes are generally white, although in Amphiprion chrysopterus they are bluish. Likewise, they are delimited by thin black lines.

There are also peculiarities of each species. Thus, some species of Amphiprion have a white line that runs along its upper part, ranging from the caudal fin to the head. 

The Amphiprion sandaracins also have a white horizontal line on the back, but it begins on the upper lip.

For Amphiprion ocellaris, the Nemo, the body is orange to reddish-brown. However, black species can be found in northern Australia. It has three vertically oriented white stripes framed by a thin black line. The first band is behind the eyes, the second is located in the middle of the body, and the last one goes around the tail. Likewise, all of the fins are lined up with black. 


On each side of the head, there is a nostril. Its small mouth contains a pharyngeal plaque. Regarding the teeth, they can be arranged in one or two rows. Their shape can resemble incisor teeth, especially in those shapes that graze algae. They can also be tapered, typically on those that capture small organisms. 


The Clownfish body has an oval shape and it is laterally compressed, giving it a rounded profile. The Clownfish has a single dorsal fin, with a total of 8 to 17 spines and between 10 and 18 soft rays. The anal fin can have between 2 or 3 spines.

The pectoral fin movement is usually rounded, which makes swimming quickly ineffective. However, in Amphiprion clarkii, the tail is emarginated or truncated, with which it can swim at a little faster speed. 


Within the Amphiprion genus, the larger individuals can reach up to 18 centimetres in length, while the smaller ones can measure between 10 and 11 centimetres. 

Immunity to neurotoxins

Clownfish have adaptations that allow them to live among the tentacles of sea anemones. This animals skin secretes a thick layer of mucus that protects them from cnidocytes. The cnidocytes are stinging cells present in the tentacles of the anemone, which contain paralysing neurotoxins.

The Clownfish mucus usually contains high proportions of glycoproteins and lipids. However, in this order of marine fish, the mucous layer gets thicker. Clownfish are not born immune to anemone toxin, but mucus prevents the body from absorbing the toxin in large amounts.

So the small doses that may be getting into the Clownfish body make them immune. This is similar to an acclimatization period before the fish becomes fully immune to the anemone sting. To reach full immunization, the Clownfish swims around the anemone and rubs its fins and belly against the ends of the anemone tentacles. 


Clownfish are born with immature female and male sexual organs. This species can change sex, which depends on environmental conditions.

The Clownfish are hermaphroditic and the male sexual organs mature first. This can lead to the misperception that all the Clownfish individuals are born male.

During courtship, the male attracts the female by spreading his fins and quickly swimming up and down. Also, the male can chase the female and nibble some parts of her body.

Before spawning, the male builds the nest in a chosen safe place and cleans it with his mouth. It can be located on a rock near or inside a sea anemone so that the tentacles protect the eggs. 

Mating and spawning

Reproduction can occur all the year around, the Clownfish do not have a reproductive period. Spawning is preceded by a bulging of the female’s abdomen and by bulging, in both sexes, of the genital tubes.

In the female, a conical white papilla of 4 to 5 millimetres in length appears. It is located in the urogenital sinus, as part of the ovipositor. In males, a urogenital duct that extends from the cloaca and measures approximately 2 millimetres surges.

Eggs are spawned while the female swims in a zig-zag fashion and rubs her belly against the nest. Once in the water, the eggs adhere to the substrate. A female can lay between 100 and 1,000 eggs depending on age.

As soon as the female spawn the eggs, the male fertilize them, which will then be laid on the nest. Eggs are capsule-shaped and orange. 

Parental care

The incubation process is affected by water temperature. So, as lower the water temperature is, the longer the incubation time will be.

During the incubation phase, both parents devour dead or unfertilized eggs. Those who are fertilized are cared for until they hatch. One of the behaviours they perform is to turn the eggs, by moving their pectoral fins. In addition, they remove the particles that cover the eggs with their mouths.

The male plays an important role in the care and protection of eggs, spending more time in the nest than the female. Progressively, as the incubation period approaches, the female increases her permanence in the nest.

Between 8 and 12 days after the spawning, the eggs hatch and the hatchlings disperse, floating in the ocean. At this stage, the offspring can be easily consumed by predators. However, after approximately two weeks, survivors begin exploring the reefs near the anemones. 


One of the Clownfish main characteristics is their territorial behaviour. They can occasionally become very aggressive. About their social structure, there are social-sexual hierarchies. The most aggressive and large female is at the highest level.

The basic social unit consists of a female Clownfish, the largest, a breeding male, and other non-breeding males, whose sexual organs have not finished developing yet.

If the female dies, the second-largest member of the group (the breeding male) will become the new female, and the largest fish in the non-reproductive group will develop the male sexual organs. In this way, he will occupy the position of the breeding male of the group. 

Symbiosis with sea anemone

Clownfish use anemones as a refuge and protect themselves from the various threats that afflict them. These animals are not characterized as experienced swimmers. Therefore, when they are in open water, they are easy prey for predators, including eels.

The tentacles of the anemone contain numerous pungent cells that are used to immobilize the anemone prey. This is how the Clownfish inside the anemone avoid being caught. In addition, anemones also protect the Clownfish nest.


In this post, we answered the question “What type of fish is Nemo?”.

We also understood more about Nemo biology and ecology.  

If you have any thoughts or doubts, feel free to drop us in a comment below!

Frequently Asked Questions (FAQs): What type of fish is Nemo?

What do Clownfish feed on?

Clownfish are not great swimmers and stay close to the host anemone, as a protective measure. Thus, they feed on the tiny particle that the anemone leaves behind. They also feed on algae and invertebrates part of the plankton.

How much food do Clownfish consume per day?

Juvenile clownfish can consume 3 to 4% of their body weight per day until they reach the sub-adult stage (7 to 9 months). Feeding will drop to around 2 to 3% as they approach adulthood.

How do Clownfish sleep?

Clownfish do not sleep, at least not like humans. For fish, there is no longer a rest period devoted to sleep. Instead, they slow down activities for a few seconds, multiple times throughout the day.

What are the Clownfish colours?

Although Clownfish are generally orange, there are species whose base is yellow, black, or pink. Usually, the stripes are white and bordered by black margins, although in some species these stripes are bluish.

How long does a Clownfish live on a tank?

In captivity, Clownfish can live between 3 and 5 years. Although, in the wild, they can live for up to a decade.


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Madhu, K., & Madhu, R. (2006). Protandrous hermaphroditism in the clown fish Amphiprion percula from Andaman and Nicobar islands. Indian Journal of Fisheries, 53(4), 373-382.

Newcomb, D. (2004). Amphiprion ocellaris. Animal Diversity Retrieved from animaldiversity.org.

Jenkins, A., Allen, G., Myers, R., Yeeting, B., Carpenter, KE (2017). Amphiprion percula. The IUCN Red List of Endangered Species 2017. Retrieved from ucnredlist.org.