Do Fish Have Periods?

Do Fish Have Periods

The answer to that question is a resounding no because their anatomy is different than a human.  

Fish also have different breeding habits and reproductive systems so it is not possible for them to have periods.  They go through spawning instead.  Having a period is a mammalian phenomenon, which means it occurs in mammals.

What Is Spawning?

 Spawning is when the eggs and sperm are deposited or released into the water.  Most aquatic animals, including fish, reproduce by spawning.  With fish, the method of fertilization can be done internally or externally.  When done internally, the female carries the eggs, and then if they are not fertilized, they are just released and are eaten by other fish.  When it is done externally, the females will release unfertilized eggs into the water in large quantities while the males release sperm at the same time to fertilize the eggs in the water.    

Most fish species will have the female laying their eggs and then the male fish will release sperm over them to fertilize the eggs.

Fish Reproduction

Most fish will lay eggs.  Most shore and freshwater fish will lay their eggs at the bottom or on plants.  When the pelagic fish lay their eggs, the eggs will usually remain suspended in open water.  The reason that they lay so many eggs is that only a few will survive as most will be eaten by other fish.  The mortality rate of the eggs and young fish is very high with just a few out of hundreds surviving.

  7 Different Types of Goldfish
sad fish

Reproductive Systems

1. Male

The male fish produce a milky white substance called milt, not sperm.  It is in their testes within their body cavity.  In sharks and rays, this duct leads to a cloaca, which is a cavity at the end of their digestive tract that is used for the release of their milt.  These fish sometimes will use their pelvic fins to help carry the milt to the eggs.  The eggs will be any place the female has laid them or at their vent.  In bony fish, they have a sperm duct that goes from the testes to their urogenital opening.  This is present behind the vent or anus.  

2. Female

The eggs of the female fish are developed in their two ovaries but some fish have just one ovary.  When they are ready to spawn and release the eggs, they go from the ovaries to the urogenital opening and releasing them into the water.  Some fish have their eggs internally fertilized and then they will be released before they start to develop.  Approximately a dozen families of the shark and bony fish will bear live young.  Skates and some rays will also have live young.   

The eggs of some of the female bony fish will let their eggs develop inside them and the young will simply emerge when the eggs hatch.  The ones that bear live young or have eggs develop in their body are provided with nourishment by the ovarian tissues after they hatch. 

The fish that produce live young have young that is relatively larger in size but fewer in number.  In the Surfperches from the Pacific coast of North America and Japan, the males of at least one species are born sexually mature although they are not fully grown.

  Black Moor Goldfish Care Guide: Diet, Breeding & More

Certain species like the cichlids will bury holes in the sand on the bottom to make nests while other fish will make nests with plant material, blow cluster of bubbles that are covered with mucus at the water surface, or with sticky thread that the fish’s kidneys excrete. 

They lay the eggs in these structures.  Some varieties of cichlids and catfish will incubate the eggs in their mouth to keep them from becoming prey.

another fish different

Maturity Stages in Female Fish

  • Resting Phase:  At this stage, the female is sexually immature.  Her ovaries are small, thin, threadlike, translucent, dirty white in color, and pale.  At this time, the ovaries only occupy a small area of her body cavity and you cannot see the ova with the naked eye.
  • Early Maturing Phase:  The ovaries at this time are larger, thicker, yellowish in color, and opaque.  They now occupy about half of her body cavity and the weight of them is increasing.  
  • Advanced Maturity Age:  The weight of the ovaries is increasing along with the volume.  They now occupy about two-thirds to three-fourths of her body cavity and are deep yellow in color.
  • Mature Phase:  This is also called the pre-spawning phase where the ovaries occupy almost all of her body cavity and are larger. They are turgid, deep yellow, and you can see with the naked eye a big number of ova through the thin ovarian wall.  There is also an increase in the blood supply to the ovaries.  They have attained their maximum weight and the ova are both translucent and opaque.  Her abdomen has become round but the eggs will not be discharged unless and until the environmental conditions are favorable.
  • Spawning Phase:  At this phase, the ovaries occupy the complete body cavity and the fish becomes very large.  The ovaries are turgid, yellow in color, and carry a lot of eggs.  The walls of the ovary are almost transparent and thin.  After the eggs enter the oviduct, the fish will spawn a number of times.
  • Spent Phase:  Now, the ovaries shrink and become flaccid, almost sac-like.  They have a dull color, the blood supply is reduced, and the volume is reduced.  There will be some small eggs and unspawned large eggs will still be in the ovaries.
  Do Aquarium Fish Vomit & How Can You Prevent It?


  • Since most of the fertilization of the eggs of a fish takes place externally, this is why fish do not have periods.  To have a period, fertilization has to happen internally.
  • Some species of bony fish and shark will bear live young.
  • In the female fish, there can be as many as six maturity states.  It depends on the size, color, and shape of the ovary.
  • When the fish are born, they do not need their mother and are pretty much on their own to find food and shelter.