How Long Is The Pregnancy Of A Fish?

The term “pregnancy” is traditionally defined as the period when the unborn young remains in a parent’s body after the egg-sperm union. For this reason, it can be tricky to apply the term “pregnancy” to fish. It is because fish are classified into livebearers and egg layers based on their breeding patterns.

How long is the pregnancy of a fish? There is no one-size-fits-all answer because of the considerable variation in the length of pregnancy between species. A dwarf seahorse, for example, has a gestation period between 3 and 55 days while the surfperch has between three and six months.

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Read on to know more about the length of pregnancy for various fish species! We classified fish into viviparous and ovoviviparous for convenience’s sake.

Viviparous Fish

When we say viviparous fish, we refer to fish that give birth to live young, a process similar to mammals that nurture the unborn fetus in the uterus. In the case of fish, the eggs develop while inside the fish parent’s body. The eggs also receive their nutrition from their parent.

Examples of viviparous fish and their gestation period in terms of the number of days are:

  • Atlantic sharpnose shark – 300 to 330
  • Blue shark – 270 to 366
  • Barbeled hound shark – more than 120
  • Blackspot shark – 270
  • Bull shark – 366
  • Lemon shark – 366
  • Daggernose shark – 366
  • Guppies – 26 to 31
  • Mollies – 60
  • Platies – 28
  • Swordtails – 28
  • Fancy guppy – 26 to 31
  • Red-tailed goodeid – 42 to 56
  • Rainbow goodeid – 55 to 60 days

Emphasis must be made that the actual days of gestation will differ between fish of the same species due to the differences in their environment.

The water temperature, light level, and nutrition have a significant influence on the gestation period and even on the number of live young.

Ovoviviparous Fish

Like viviparous fish, ovoviviparous fish also give birth to live young. But their embryos received nutrition from an egg yolk instead of directly from their parent, usually a female.

Ovoviviparous fish are also known as egg-laying fish because their embryos appear like eggs floating in the water.

Examples of ovoviviparous fish and their gestation periods in days are:

  • Goldfish – 2 to 7
  • Zebra danio – about 2
  • Glowlight tetra – about 2
  • Tiger barb – 3 to 5
  • White cloud mountain minnow – 2 to 3
  • Basking ray – 270 to 366
  • Coelacanth – More than 366
  • Blue stingray – 270
  • Sailfin molly – 21 to 28
  • Tiger shark – 30 to 480

There are species of fish where the male becomes pregnant instead of the female, including pipefishes, seahorses, and weedy and leafy sea dragons. In these species, the male incubates the eggs in their bodies before releasing live fry into the water.

The method of incubation varies, too, such as the male seahorses having a specialized brood pouch and the male sea dragons attaching the eggs to their legs.


To conclude, breeding livebearers and egg layers in an aquarium can be easy if and when you have the know-how. You should read information resources first, such as  The Complete Illustrated Breeder’s Guide to Marine Aquarium Fishes, before attempting fish breeding.

You will also need equipment, such as the Petzilla Aquarium Fish Breeder Box for Baby Fish Hatchery, to boost your chance of success.