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1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problemsOviparous reproduction is egg-laying reproduction. In an oviparous fish, fertilized eggs are laid outside the mother’s body. The embryo develops in the egg and is nourished by its yolk rather than by a placenta or direct maternal supply.
What does oviparous mean in fish?
Oviparity describes where the egg develops and how the embryo is nourished: the egg is deposited outside the female, and the embryo uses nutrients stored in the yolk. OpenStax’s Biology 2e defines it this way: “In oviparity, fertilized eggs are laid outside the parent’s body and develop there, receiving nourishment from the yolk that is a part of the egg.”
The term is not defined solely by the location of fertilization. Fertilization may occur outside the body, as in many spawning fish, or inside the female before she deposits an egg case.
How most oviparous fish reproduce
Spawning in water
Most fish are oviparous, and nearly all fish spawn. In the familiar pattern used by many bony fish, the female releases eggs into the water and the male releases sperm over them. Fertilization then occurs externally, and the embryos develop in the eggs outside the female.
What the embryo uses for food
The embryo depends on yolk packaged inside the egg. Oviparous reproduction does not involve placental nourishment from the mother. After hatching, the young fish may still rely on a remaining yolk sac for a short time, depending on the species.
Is fertilization always external in oviparous fish?
No. External fertilization is common, but it is not a requirement for oviparity.
Some oviparous sharks and rays fertilize internally. The developing embryo is enclosed in an egg case, which the female deposits in the environment. In these species, the egg is still laid outside the mother and the embryo is still nourished by yolk, so the reproduction is oviparous even though fertilization occurred inside her body.
The FAO describes forms of elasmobranch egg laying, including extended oviparity, in which most development takes place after the egg case is deposited, and rarer retained oviparity, in which the egg is held longer before deposition.
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Oviparous, ovoviviparous, and viviparous fish compared
| Mode | Are eggs laid outside the mother? | Where does development occur? | Main embryonic nourishment | Typical fertilization pattern |
|---|---|---|---|---|
| Oviparous | Yes | Outside the mother, in an egg or egg case | Yolk in the egg | Often external, but sometimes internal |
| Ovoviviparous | Not before hatching | Inside the female until the eggs hatch | Yolk in retained eggs | Usually internal |
| Viviparous | No; young are born live | Inside the female | Direct maternal nourishment, rather than yolk alone | Usually internal |
These categories are based mainly on egg retention, the location of embryonic development, and the source of nourishment. They should not be reduced to a simple external-versus-internal fertilization rule.
Are all fish oviparous?
No. “Fish” includes species with several reproductive strategies. Most fish are oviparous, but some are ovoviviparous and others are viviparous. Sharks illustrate this variety: some species lay egg cases, while others give birth to live young. Therefore, “all fish lay eggs externally” is inaccurate.
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No precise, authoritative percentage for the proportion of all fish that are oviparous is established by the cited sources. The accurate generalization is qualitative: most fish are oviparous, and nearly all fish spawn.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.The Bottom Line
Bottom line: An oviparous fish lays eggs outside its body, and the embryo develops in those eggs using yolk. Fertilization is often external but can be internal, as in some egg-laying sharks and rays.
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