Do fish have sex?

In this post, we will answer the question “Do fish have sex?”. We will also discuss a few curiosities about fish gender change.    

Do fish have sex?

Fish, yes, have sex. Almost every multicellular species has the same natural drive: to live as long as possible to reproduce as many times as possible throughout a lifetime. More kids surviving to adulthood and spawning age means more genes remain in the gene pool. 

This has long been referred to as “fitness” by scientists. The fitter an animal is, the more genes from that animal are found in a population. You’re a Darwinian zero if you don’t reproduce at all. In our mammalian environment, even non-scientists have a good understanding of reproduction. Copulation happens when males and females exchange genes, and fertilization occurs within. The offspring then develop within the mother for the most part until birth.

Fish have developed a staggering array of reproduction techniques that range from everyday to the bizarre to the unbelievable. 

Reproduction in Fish: The Fundamentals 

Here are a few key life-history characteristics to consider while studying fish reproduction. 

Maturity age

The average age at which a species is capable of reproducing. This is mainly predicated on females; males are less important. Once a fish reaches reproductive maturity, it does not change. In fish, there isn’t much indication of sexual senescence (becoming too old to reproduce). 


The number and size of eggs produced are measured using this metric. Larger fish produce a higher proportion of eggs than smaller fish. 

Frequency of spawning

Forage fish, including tiny forage fish and even bigger species such as salmon, are semelparous, meaning that they breed just once in their lifetimes. Iteroparous species, on the other hand, spawn many times during their existence. 

We notice trade-offs linked with these criteria, as we do with most things in life. For example, producing gametes, particularly eggs, is a high-energy operation. Energy is redirected to reproductive organs, resulting in a reduction in the quantity of energy available to support growth.

Because there is a greater pressure to reproduce at least once before dying, such a physiological strategy works well for fish with short life spans. However, for species that live longer, this isn’t always the ideal approach because putting all of your energy into reproduction early on stifles growth. Furthermore, fish must grow swiftly to avoid natural death from larger predators. 

It is also possible to make trade-offs when it comes to the amount and size of eggs produced at any one particular spawning event. Because smaller eggs require less energy to develop, more can be produced. It has the drawback of producing smaller larvae, which are more prone to natural mortality as a result of their lower size. Larger eggs produce larger larvae, giving the fry a better chance of survival. 

Eggs hatch as fully developed juveniles in some situations, such as with some sharks and rays (elasmobranchs), thereby skipping the larval stage.Some elasmobranchs, such as big hammerhead sharks, exhibit viviparity, or live birth, which is unusual.

Sharks that are viviparous form a placental connection with their offspring and give extra nutrition throughout development. A huge number of young are born alive and in good health, which boosts their chances of survival. Ovoviviparous sharks, such as nurse sharks, give birth to live young too, but there is no placental connection between the mother and the young; the energy required for growth is derived entirely from the yolk of the egg.

Fish spawning

The majority of fish spawn by releasing eggs and sperm directly into the water column in order to accomplish fertilization. Depending on the situation, this can be done individually or in a group environment. Many salmonid species prefer a more personal and monogamous relationship. One of the advantages of this procedure is that just one male’s sperm may fertilize a batch of eggs, which reduces the number of eggs that need to be fertilized. Freshwater cichlids, whose males and females work together to build nests before spawning and protect the eggs from predators, are another example of how monogamy may be beneficial.

Fish commonly undertake group spawning, which has its own set of benefits. Because there are more eggs and sperm in the water at one moment, large aggregations of fish that spawn at the same time may have a better chance of fertilization. It’s also a strategy for avoiding predators who prey on fertilized eggs: The spawners make it nearly impossible for other fish to swallow all of the eggs they produce, ensuring that at least some of them survive to hatch. 

Snappers and groupers, for example, congregate in spawning aggregations for just these reasons. Anglers have been targeting these aggregations for generations since the fish are easier to catch, which can lead to overharvesting in some circumstances. As a result, during spawning seasons, fisheries managers frequently use rules to safeguard fish. 

External fertilization isn’t used by all fish to reproduce. Copulation, which happens in cartilaginous fish such as sharks and rays, results in the fertilization of the eggs within the animal. A pair of claspers can be found beneath the pelvic ends of males. Claspers perform the same role as the mammalian penis in delivering sperm to the female. 

During copulation, males only use one clasper. Because the organs grow on the inner border of the pelvic fins, which are paired, they have two claspers to hold them in place throughout development.

Male sharks must keep in contact with female sharks to copulate. Given that sharks lack the ability to grasp objects with their hands, they must rely on their teeth. These love bites are most commonly seen around the head, gills, and pectoral fins, and they provide the required leverage for a clasper to be placed into the female’s body.

Copulation can look to be rather aggressive. Nurse sharks, for example, struggle and copulate in relatively shallow water. Pelagic sharks frequently copulate in the middle of the ocean; once the clasper is implanted, they stop swimming and fall to the bottom. 

Female sharks are also one of the few vertebrates, if not the only fish, who are capable of reproducing on their own without the assistance of a male spouse. I’m talking about real-life virgin birth and the Immaculate Conception. Parthenogenesis, or asexual reproduction, is assumed to have evolved as a response to a shortage of partners. 

Parthenogenesis has been reported in captive bonnethead blacktip and zebra sharks in the absence of males, according to the research. While this technique allows for offspring production in the absence of mates, it is not considered adaptive because it does not promote genetic variety in a population.

Are fish capable of changing gender?

While the majority of species are gonochoristic, meaning they have clearly defined, separate sexed individuals in the community, some are hermaphroditic. Hermaphrodites are characterized by the presence of both male and female reproductive organs. This approach has been observed in 20 distinct groups of fish, including game fish like snapper and grouper. What’s more intriguing is the fact that hermaphroditism is regarded to be a more recent reproductive strategy than gonochorism. 

Hermaphroditism is usually a two-step process: fish are born in one gender and then switch to the other as they grow older or larger. Protogyny is the term used by scientists to describe the transformation of female fish into males. Protogynous hermaphrodites include wrasses, parrotfish, and a variety of groupers, including reds and blacks. 

Protogyny might be advantageous evolutionarily in instances where male reproductive output increases faster than female reproductive production. This scenario also benefits females sexually selecting larger guys. In settings where giant males can monopolize mating, the large male size is regarded to be adaptive. 

Protogyny is most common in animals with harem social dynamics (one male and several tiny females), where large, powerful males make the decisions about who mates with whom. 

Fish classed as protandrous hermaphrodites, on the other hand, are born male and mature into females at a later age and size. A male snook, for example, is born. When they reach reproductive maturity, they are about the age of 18 inches, and sexual reversal takes place in the fall following the summer spawn, generally when they are between the ages of 1 and 6. 

When it comes to physical size, protandry makes a great deal of sense. The production of sperm is modest and low-cost when compared to the production of eggs, and even little guys may generate enough sperm to fertilize an almost unlimited number of eggs.

Egg production, once again, demands more energy and room. Females who are larger generate disproportionately more eggs than smaller females. 

From a fecundity standpoint, you’d assume protandry would be the better option. Surprisingly, protandry is significantly less common than protogyny. Protandry is thought to be rarer because it frequently results in male-biased sex ratios, which promote an excessive amount of surplus sperm that is wasted. 

Only a few fish species can simultaneously generate eggs and sperm. The synchronous hermaphroditism of some of the more obscure, smaller members of the grouper family has been seen, although it has been very seldom observed in game fish.

Even though synchronous hermaphrodites are capable of producing both gametes at the same time, they rarely self-fertilise. Individual role-playing between male and female with mates throughout the spawning phase. Here, the evolutionary advantage favours situations where mates are scarce. When one of these fish encounters another of its kind, it never has to worry about being incompatible.


In this post, we answered the question “Do fish have sex?”. We also discussed a few curiosities about fish gender change.  

If you have any questions or concerns, please let us know in the comments section below!

Frequently Asked Questions (FAQs): Do fish have sex?

How can fish reproduce sexually? 

Almost all fish reproduce through sexual reproduction, which involves the union of sperm from tests and eggs from ovaries. In most fish species, fertilisation is done externally. Females and males both discharge large amounts of eggs and sperm into the water at the same time. 

What is the process by which fish mate? 

In the vast majority of cases, the female drops eggs in the water, which are fertilised nearly quickly by sperm from the male present. Other methods include fertilisation taking place inside the female body prior to the eggs being placed in the water by the mother. In the third and final approach, the mother retains the eggs within her body, and the young are born alive. 

What is the best way to know whether a fish is having a fling?

Males are often leaner, but larger-bodied, and have more bright colours than females. In comparison to the female, the male’s dorsal and anal ends are more pointed, bigger, more flowing. In several species, the male’s anal fin will have egg-shaped marks known as egg spots. 

Is it true that male fish experience orgasms? 

Male fish use “some form of intromittent apparatus to carry sperm into the vaginal entrance of the female,” according to the study, and 97 per cent of fish fertilize their eggs internally. 

Is it true that fish have periods? 

Fish, on the other hand, do not have periods. Fish eggs are fertilized externally during reproduction, while those that reproduce internally do not have periods. 

What causes goldfish to become pregnant? 

Unlike many tropical fish, such as guppies and swordtails, which give birth to live young, goldfish reproduce by depositing eggs. 

Is my goldfish expecting a baby? 

Because goldfish can’t carry live babies inside their bodies, they can’t be pregnant. They throw unfertilized eggs into the water, where the male fertilizes them before they hatch. Until then, she’s merely carrying the possibility of a baby goldfish.


How Do Fish Have Sex?-

How Do Fish Have Sex? –