Wednesday, July 17, 2024

Female Fish and their Reproductive Strategies: All You Need to Know About

A female fish posses some unique characteristics that different them from their male counterparts. Today we are looking at the female fish reproductive strategies and how to identify a female fish from a male fish. Fish reproductive organs include testes and ovaries.

In most species, gonads are paired organs of similar size, which can be partially or totally fused. There may also be a range of secondary organs that increase reproductive fitness. The genital papilla is a small, fleshy tube behind the anus in some fishes, from which the sperm or eggs are released; the sex of a fish often can be determined by the shape of its papilla.

Meanwhile, some female fish can create a new species if their partners are hot enough. This means that if her suitor is particularly handsome or if she can’t see him properly then a female fish will mate outside her species. And that, according to new research from an international team of scientists, can lead to her giving birth to entirely new and diverse species of fish.

With regards to what a female fish is called, A female fish does not have a specific name, male and female fish are both just called fish. However, around 500 species of fish are able to change their gender during their later life after birth. A species of fish that can change its gender is called a hermaphrodite.

The only names that are attributed to both the male fish and the female fish are as follows:


A group of fish is often simply referred to as a shoal of fish, this is when the fish are swimming in no specific orderly fashion or direction. They usually stay together because it provides “safety in numbers” and to avoid being the meal of a predator by sheer size and congregation.


A school of fish is slightly different from a shoal in that a large number of fish are moving as a single unit with a purpose. This purpose is likely to be due to migration to warmer/colder climates or to find an area with an abundant amount of food.

Now let us look at the major differences between a male and a female fish and how to tell the difference between a male and female fish

There are many ways to tell the difference between the two, so let’s go through them.


Male fish tend to have larger but thinner bodies, meaning they are generally taller and longer than female fish

Has more vibrant colors

Usually male fish have more vibrant colors compared to female fish, this is mainly during mating season, however, female fish can have more vibrant colors when producing eggs. Male and female fish colors can become more vibrant when fed a healthy diet usually when owned as a pet.

Pointier fins

The fins on a male fish tend to protrude further out from the body meaning that the dorsal and anal fins of a male fish usually extend out more than that of a female fish. This makes then generally larger and more free-flowing.

Meanwhile with regards to how to tell the difference between a male fish and female fish, looking at a male or female fish in isolation will make it hard to tell without being able to make a visual comparison next to the opposite gender.

Telling the size can also depend on the species of fish. If you know what species you are identifying the gender of the fish and if you know the correct size, you might be able to estimate the gender by knowing the average size of the species and whether your fish is bigger or smaller.

There are some recently discovered ways that anyone can use to determine the sex of the fish as we discuss below:

Depending on the species, determining the sex of a fish ranges from easy to nearly impossible. Knowing the sexual differences in aquarium fish is important when trying to breed fish and also for choosing the proper balance of fish for a community aquarium. Although not all fish can be easily identified by sex, these tips will help you recognize the sex of many of the common species of aquarium fish.

Read Also: Female Fish are more Reluctant to Change Sex than Males

Determining Fish Sex: Female Fish or Male Fish

Here is how you can figure out the sex of common aquarium fish. This is by no means an exhaustive list but it does provide a general overview of the differences between the fish sexes.


Angelfish are extremely difficult to know accurately which is which sex, particularly when they are young. Occasionally fully mature males will show a modest nuchal hump, which is a bump on the head just above the eyes.

Don’t count on it being there in every case, though. The best way to establish a mating pair is to purchase a half-dozen immature angelfish and raise them together.

When they are mature enough, they will pair off, and you should have at least one breeding pair out of the group. Once they begin mating, it will be quite obvious which one is male fish and which is female fish as she will be the one with the ovipositor laying the eggs. The ovipositor is a short tube from the female’s vent that she uses to lay her eggs. It has a rounded tip.

The male will use a pointed tube that extends from his vent to fertilize the eggs after they are laid by the female. Both parents will take turns hovering over the eggs, fanning them with their fins to oxygenate them and keep them clean.


Bettas are a species of fish that is quite easy to identify their sexes. Male fish have the long flowing fins and brilliant colors that owners find attractive.

Male fish of bettas are the ones usually sold in shops. Their female fish are not as vividly colored and have short, stubbier fins, but some male fish of betta varieties can also have short fins.

It is not always easy to find female fish bettas for sale in pet shops; if you can’t locate one, ask the shop owner or manager if they can order one for you. Male fish bettas must be kept separate from each other and from the female until she is ready to breed.

The male builds a nest out of air bubbles on the surface of the water and then entices the female to lay her eggs under it, wrapping his body around hers to fertilize the eggs as she lays them.

He then collects the eggs into his mouth and places them into his bubble nest. After breeding, the male chases the female away and takes care of the eggs and the babies. The female fish must be removed or she will be attacked by the male.


Generally speaking, catfish sexes cannot be distinguished. Many species of catfish have not been breed in captivity. The notable exception is the Corydoras species, which has often been breed in captivity. In the Corydoras catfish, the female fish is usually a bigger-bodied fish than the males.

The male fish will chase a gravid female (full of eggs) around the tank and then she will lay the eggs on a flat surface, such as a plant leaf, smooth rock, or even the aquarium glass. The male fish will swim over the eggs and fertilize them, then the eggs are abandoned.


Cichlids are such a diverse group that it would take a small novel to give specifics for knowing the difference within each species. While many are not easily differentiated, there are a few rules of thumb that apply to quite a few cichlid species.

Males are often slimmer but larger-bodied than females and are more vibrantly colored. The dorsal and anal fins of the male are more pointed, larger and more flowing than in the female. In many species, the male will display egg-shaped markings on the anal fin known as egg spots.

Some males have a bump on the head, referred to as a nuchal hump. Although females can also develop a nuchal hump when spawning, it is never as prominent as that of the male. Typically the dominant male will have a larger nuchal hump than other males.

Although the above general rules apply to many species of cichlids, if you are considering breeding them, do your homework on the specific species before seeking a breeding pair.


Barbs and other members of the cyprinid family are rather difficult to tell apart. Differences will vary by species, but generally, males are more intensely colored and slimmer than female fish. Since most cyprinids are schooling fish, one way to obtain a breeding pair is to purchase a group of them.

In some species of cyprinids, including goldfish, the males will get small white bumps (nuptial tubercles) on their head, operculum and possibly the spine of the pectoral fins during the mating season.

The males will chase the female who will lay her eggs and the males fertilize them as she deposits them. After breeding, usually there is no care of the eggs, and the parents may even eat them if they are found.


Gouramis are another species of fish that are not easily identified. Males and females often are similarly colored and shaped. There is, however, one fairly universal sexual difference seen in most gourami species. The dorsal fin is long and comes to a distinct point in males, while females have a shorter, rounded dorsal fin.

In addition, certain species of gourami show color variations between the female fish and male fish sexes. The male pearl gourami has a deep red-orange coloration on the throat and breast. The male fish of moonlight gourami has orange to red coloration of the pelvic fins. Like the betta, many gouramis will build a bubble nest, but both the male and female are involved in taking care of the eggs.

Live bearing Fish

Among the easiest of all fish to tell apart are the livebearing fish, such as the guppies, platys, mollies, and swordtails. The male fish are usually smaller and more colorful than female fish.

They also possess an external sexual organ, the gonopodium, which makes it easy to differentiate male fish from the female fish: In the male fish, the anal fin is rod-shaped, while the female has a traditional fan-shaped anal fin.

The gonopodium is used to fertilize eggs inside of the female fish as the male swims alongside the female. The internally fertilized eggs will hatch inside the female and then she will “give birth” to the babies.


Tetras do have some differences between sexes, which vary based on the species. The females are a bit larger and plumper than males. Male fish are often more vibrantly colored and may have longer fins than their female counterparts.

Tetras are schooling fish, so breeding pairs can be obtained simply by purchasing a small school of them at one time. Generally, they breed by the male fish chasing the female fish and fertilizing the eggs as she lays them in the plants or scattered among the rocks. There is no parental care to the eggs, which may be eaten if discovered by the fish.

Related: The Effect of Heat Stress on Animal Productivity

Fish Reproductive Strategies

Female Fish
Female Fish with Make-Ups….. Smiles!

In fish, fertilization of female fish eggs can be either external or internal. In many species of fish either on female fish and male fish, fins have been modified to allow Internal fertilization. Similarly, development of the embryo can be external or internal, although some species show a change between the two at various stages of embryo development.

Thierry Lodé described reproductive strategies in terms of the development of the zygote and the interrelationship with the parents; there are five classifications – ovuliparity, oviparity, ovo-viviparity, histotrophic viviparity and hemotrophic viviparity.


Ovuliparity means the female lays unfertilized eggs (ova), which must then be externally fertilized. Examples of ovuliparous fish include salmon, goldfish, cichlids, tuna and eels. In the majority of these species, fertilization takes place outside the mother’s body, with the male and female fish shedding their gametes into the surrounding water.


Oviparity is where fertilization occurs internally and so the female sheds zygotes (or newly developing embryos) into the water, often with important outer tissues added. Over 97% of all known fish are oviparous. In oviparous fish, internal fertilization requires the male to use some sort of intromittent organ to deliver sperm into the genital opening of the female.

Examples include the oviparous sharks, such as the horn shark, and oviparous rays, such as skates. In these cases, the male is equipped with a pair of modified pelvic fins known as claspers.

Marine fish can produce high numbers of eggs which are often released into the open water column. The eggs have an average diameter of 1 millimetre (0.039 in). The eggs are generally surrounded by the extraembryonic membranes but do not develop a shell, hard or soft, around these membranes. Some fish have thick, leathery coats, especially if they must withstand physical force or desiccation. These type of eggs can also be very small and fragile.

The newly hatched young of oviparous fish are called larvae. They are usually poorly formed, carry a large yolk sac (for nourishment) and are very different in appearance from juvenile and adult specimens.

The larval period in oviparous fish is relatively short (usually only several weeks), and larvae rapidly grow and change appearance and structure (a process termed metamorphosis) to become juveniles. During this transition larvae must switch from their yolk sac to feeding on zooplankton prey, a process which depends on typically inadequate zooplankton density, starving many larvae.


In ovoviviparous fish the eggs develop inside the mother’s body after internal fertilization but receive little or no nourishment directly from the mother, depending instead on a food reserve inside the egg, the yolk. Each embryo develops in its own egg. Familiar examples of ovoviviparous fish include guppies, angel sharks, and coelacanths.


There are two types of viviparity, differentiated by how the offspring gain their nutrients.

  • Histotrophic (tissue eating) viviparity means embryos develop in the female’s oviducts but obtain nutrients by consuming other tissues, such as ova (oophagy) or zygotes. This has been observed primarily among sharks such as the shortfin mako and porbeagle, but is known for a few bony fish as well such as the halfbeak Nomorhamphus ebrardtii. An unusual mode of vivipary is adelphophagy or intrauterine cannibalism, in which the largest embryos eat weaker, smaller unborn siblings. This is most commonly found among sharks such as the grey nurse shark, but has also been reported for Nomorhamphus ebrardtii.
  • Hemotrophic (blood eating) viviparity means embryos develop in the female’s (or male’s) oviduct and nutrients are provided directly by the parent, typically via a structure similar to, or analogous to the placenta seen in mammals. Examples of hemotrophic fish include the surfperches, splitfins, lemon shark, seahorses and pipefish.

Aquarists commonly refer to ovoviviparous and viviparous fish as livebearers.


Hermaphroditism occurs when a given individual in a species possesses both male and female reproductive organs, or can alternative between possessing first one, and then the other. Hermaphroditism is common in invertebrates but rare in vertebrates.

It can be contrasted with gonochorism, where each individual in a species is either male or female, and remains that way throughout their lives. Most fish are gonochorists, but hermaphroditism is known to occur in 14 families of teleost fishes.

Usually hermaphrodites are sequential, meaning they can switch sex, usually from female to male (protogyny). This can happen if a dominant male is removed from a group of females. The largest female in the harem can switch sex over a few days and replace the dominant male.

This is found amongst coral reef fishes such as groupers, parrotfishes and wrasses. It is less common for a male to switch to a female (protandry). As an example, most wrasses are protogynous hermaphrodites within a haremic mating system. Hermaphroditism allows for complex mating systems. Wrasses exhibit three different mating systems: polygynous, lek-like, and promiscuous mating systems.

Group spawning and pair spawning occur within mating systems. The type of spawning that occurs depends on male body size. Labroids typically exhibit broadcast spawning, releasing high amounts of planktonic eggs, which are broadcast by tidal currents; adult wrasses have no interaction with offspring. Wrasse of a particular subgroup of the family Labridae, Labrini, do not exhibit broadcast spawning.

Less commonly hermaphrodites can be synchronous, meaning they simultaneously possess both ovaries and testicles and can function as either sex at any one time. Black hamlets “take turns releasing sperm and eggs during spawning.

Because such egg trading is advantageous to both individuals, hamlets are typically monogamous for short periods of time–an unusual situation in fishes.” The sex of many fishes is not fixed, but can change with physical and social changes to the environment where the fish lives.

Particularly among fishes, hermaphroditism can pay off in situations where one sex is more likely to survive and reproduce, perhaps because it is larger. Anemone fishes are sequential hermaphrodites which are born as males, and become females only when they are mature.

Anemone fishes live together monogamously in an anemone, protected by the anemone stings. The males do not have to compete with other males, and female anemone fish are typically larger.

When a female dies a juvenile (male) anemone fish moves in, and “the resident male then turns into a female and reproductive advantages of the large female–small male combination continue”. In other fishes sex changes are reversible. For example, if some gobies are grouped by sex (male fish or female fish), some will switch sex.

The mangrove rivulus Kryptolebias marmoratus produces both eggs and sperm by meiosis and routinely reproduces by self-fertilization. Each individual hermaphrodite normally fertilizes itself when an egg and sperm that it has produced by an internal organ unite inside the fish’s body.

In nature, this mode of reproduction can yield highly homozygous lines composed of individuals so genetically uniform as to be, in effect, identical to one another. The capacity for selfing in these fishes has apparently persisted for at least several hundred thousand years.

Although inbreeding, especially in the extreme form of self-fertilization, is ordinarily regarded as detrimental because it leads to expression of deleterious recessive alleles, self-fertilization does provide the benefit of fertilization assurance (reproductive assurance) at each generation.

Sexual parasitism

Sexual parasitism is a mode of sexual reproduction, unique to anglerfish, in which the males of a species are much smaller than the females, and rely on the females for food and protection from predators. The males give nothing back except the sperm which the females need in order to produce the next generation.

Some anglerfish, like those of the deep sea ceratioid group, employ this unusual mating method. Because individuals are very thinly distributed, encounters are also very rare. Therefore, finding a mate is problematic. When scientists first started capturing ceratioid anglerfish, they noticed that all the specimens were female.

These individuals were a few centimetres in size and almost all of them had what appeared to be parasites attached to them. It turned out that these “parasites” were highly reduced male ceratioid anglerfish. This indicates the anglerfish use a polyandrous mating system.

The methods by which the anglerfish locate mates are variable. Some species have minute eyes unfit for identifying females, while others have underdeveloped nostrils, making it unlikely that they effectively find females using olfaction.

When a male finds a female, he bites into her skin, and releases an enzyme that digests the skin of his mouth and her body, fusing the pair down to the blood-vessel level. The male becomes dependent on the female host for survival by receiving nutrients via their now-shared circulatory system, and provides sperm to the female in return.

After fusing, males increase in volume and become much larger relative to free-living males of the species. They live and remain reproductively functional as long as the female stays alive, and can take part in multiple spawnings.

This extreme sexual dimorphism ensures that when the female is ready to spawn she has a mate immediately available. Multiple males can be incorporated into a single individual female with up to eight males in some species, though some taxa appear to have a one male per female rule.

One explanation for the evolution of sexual parasitism is that the relative low density of females in deep-sea environments leaves little opportunity for mate choice among anglerfish.

Females remain large to accommodate fecundity, as is evidenced by their large ovaries and eggs. Males would be expected to shrink to reduce metabolic costs in resource-poor environments and would develop highly specialized female-finding abilities.

If a male manages to find a female parasitic attachment, then it is ultimately more likely to improve lifetime fitness relative to free living, particularly when the prospect of finding future mates is poor.

An additional advantage to parasitism is that the male’s sperm can be used in multiple fertilizations, as he stays always available to the female fish for mating. Higher densities of male-female encounters might correlate with species that demonstrate facultative parasitism or simply use a more traditional temporary contact mating.


Parthenogenesis is a form of asexual reproduction in which growth and development of embryos occur without fertilization. In animals, parthenogenesis means development of an embryo from an unfertilized egg cell. The first all-female (unisexual) reproduction in vertebrates was described in the Amazon molly in 1932.

Since then at least 50 species of unisexual vertebrate have been described, including at least 20 fish, 25 lizards, a single snake species, frogs, and salamanders. As with all types of asexual reproduction, there are both costs (low genetic diversity and therefore susceptibility to adverse mutations that might occur) and benefits (reproduction without the need for a male) associated with parthenogenesis.

Parthenogenesis in sharks has been confirmed in the bonnethead and zebra shark.Other, usually sexual species, may occasionally reproduce parthenogenetically, and the hammerhead and blacktip sharks are recent additions to the known list of facultative parthenogenetic vertebrates.

A special case of parthenogenesis is gynogenesis. In this type of reproduction, offspring are produced by the same mechanism as in parthenogenesis, however, the egg is stimulated to develop simply by the presence of sperm as the sperm cells do not contribute any genetic material to the offspring. Because gynogenetic species are all female fish, activation of their eggs requires mating with males of a closely related species for the needed stimulus.


The elkhorn sculpin (Alcichthys elongatus) is a marine teleost with a unique reproductive mode called “internal gametic association”. Sperm are introduced into the ovary by copulation and then enter the micropylar canal of ovulated eggs in the ovarian cavity. However, actual sperm-egg fusion does not occur until the eggs have been released into sea water.


Benadine Nonye is an agricultural consultant and a writer with several years of professional experience in the agriculture industry. - National Diploma in Agricultural Technology - Bachelor's Degree in Agricultural Science - Master's Degree in Science Education - PhD Student in Agricultural Economics and Environmental Policy... Visit My Websites On: 1. - Your Comprehensive Practical Agricultural Knowledge and Farmer’s Guide Website! 2. - For Effective Environmental Management through Proper Waste Management and Recycling Practices! Join Me On: Twitter: @benadinenonye - Instagram: benadinenonye - LinkedIn: benadinenonye - YouTube: Agric4Profits TV and WealthInWastes TV - Pinterest: BenadineNonye4u - Facebook: BenadineNonye

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