If you’ve ever seen a school of tiny fish swimming around and wondered where they came from, learning about fish eggs can provide some answers. Fish lay eggs that contain developing embryos which will hatch into baby fish, allowing species to reproduce and maintain their populations.

If you’re short on time, here’s a quick answer to your question: Fish eggs that contain developing embryos and will hatch into baby fish are called fish roe or fish spawn.

In this comprehensive article, we’ll explore everything you need to know about what fish eggs are called, the different types of fish eggs, their characteristics, development process, and more.

Terminology and Names for Fish Eggs

Fish Roe

Fish roe refers to the fully egg-laden ovary of a female fish. It contains fertilized and unfertilized eggs that are still enclosed in the ovarian tissue. Roe can come from various types of fish like salmon, trout, herring, cod, sturgeon, and mullet.

Fish roe is considered a delicacy in many cuisines like Japanese, Italian, French, and Russian. It can be served fresh or processed by salting, smoking, or pickling. Some popular types of fish roe are salmon roe (ikura), herring roe (kazunoko), shrimp roe (ebisu), and cod roe (tarako).

Fish Spawn

Fish spawn refers to the mass release of eggs and sperm by fish during the spawning process. Unlike solitary species that lay a nest of eggs for the male to fertilize, schooling fish like anchovies and herring gather together in large numbers to simultaneously release eggs and milt into the water to achieve external fertilization.

According to a NOAA report, a single female fish can produce between 500 to 15 million eggs during the spawning period. After fertilization, the fertilized eggs will hatch into larvae and eventually mature into adult fish.


Caviar specifically refers to salted roe from wild sturgeon. Based on a 2021 industry report, retail caviar prices can range between $50 to $10,000 per kilogram. True caviar comes from the Caspian and Black Sea where species like beluga sturgeon, Russian sturgeon, sterlet sturgeon, and sevruga sturgeon reside.

Due to overfishing, sturgeon population and caviar production have declined, leading other roes like salmon roe, tobiko (flying fish roe), trout roe, lumpfish roe, and whitefish roe to be marketed as caviar too.

In the past decade, the production of farmed or “malossol” caviar has been on the uptrend. Malossol refers to the light salting method that retains the eggs’ supple texture. Several sturgeon species like Siberian sturgeon, Adriatic sturgeon, and white sturgeon are bred on aqua farms in Italy, Israel, and California specifically for caviar production.

Based on a Fortune Business Insights report, the global caviar market is projected to grow from $766.2 million in 2021 to $1,089.1 million in 2028 due to sustainable aquaculture efforts. Nonetheless, connoisseurs still prefer Caspian wild caviar for its unique flavor and texture.

Types of Fish Eggs and Their Characteristics

Large Eggs With Lots of Yolk

Fish that lay large eggs full of yolk tend to be pelagic spawners like tuna, cod, and bass. These free-floating eggs contain ample nutrients to sustain the embryo until hatching. The abundant yolk allows the larval fish to undergo substantial development before needing to hunt for external food sources.

For instance, Atlantic cod lays eggs up to 4 mm wide that float near the ocean’s surface. The high yolk content enables the cod larvae to subsist for nearly two weeks after hatching while their jaws and digestive system grow strong enough to capture prey.

Small Eggs With Little Yolk

Conversely, fish with small, yolk-deficient eggs usually spawn them directly onto vegetation or buried in riverbeds and lake floors. Examples include trout, catfish, and minnows. Rather than float adrift, the eggs remain safely hidden away while the embryos develop.

Since less yolk means less innate nutrients, the hatched larvae immediately start hunting microscopic particles to eat. So species like rainbow trout produce tiny eggs just 2-3 mm wide, but there are lots of insects and zooplankton for the fry to start feeding on right away.

Adhesive Eggs

Most fish eggs feature an outer adhesive coating so they can stick to aquatic plants, rocks, logs, and other submerged surfaces. This sticky covering protects the developing embryos by securing the eggs in sheltered spots to limit disturbance or predation.

According to a 1994 study, the adhesive property evolved as a reproductive strategy to maximize hatching success. Data showed egg adhesion resulting in 65% greater survival rates compared to non-adhesive eggs drifting haphazardly.

Non-Adhesive Eggs

Non-adhesive or buoyant eggs primarily belong to pelagic spawning fish species like tuna, marlin, and sea turtles. Since the fertilized eggs float freely in open oceans, they drift along with the currents until hatching.

Non-Adhesive Pelagic Spawners Typical Egg Diameter
Albacore tuna 1.2 – 1.6 mm
Atlantic bluefin tuna 1.4 – 2.0 mm
Ocean sunfish 5.0 – 8.0 mm

These species produce small, buoyant eggs sometimes by the hundreds of thousands. But only a tiny fraction naturally survives to adulthood despite the sheer quantities spawned.

The Fish Egg Development Process


Fertilization occurs when the sperm meets the egg. The sperm must penetrate the outer layers of the egg in order to combine genetic material and initiate embryonic development. This activates the egg, allowing cell division and growth to begin (animaldiversity.org).

Fertilization generally happens externally for most fish species, taking place in the water shortly after the eggs are released from the female and the male releases sperm.

Cell Cleavage

During cell cleavage, the fertilized egg rapidly divides into many cells within a membrane called the chorion. The cells divide without increasing in size, resulting in smaller cells called blastomeres. This orderly division results in a round cluster of cells known as a blastula (khanacademy.org).

Cleavage allows for early differentiation of cell groups that will develop into specialized tissues and organs.


Gastrulation reorganizes the cells into distinct layers with different fates. Cells migrate inward along the blastula surface to form two or three germ layers. Each germ layer will give rise to different tissues and organs.

The three main germ layers in fish are the ectoderm, mesoderm, and endoderm (Britannica.com). The ectoderm forms the nervous system and outer skin cells, the mesoderm forms muscle and connective tissues, and the endoderm forms digestive organs.


During organogenesis, the germ layers begin rapidly differentiating and forming into tissues and organs in a process called morphogenesis. Cell interactions coordinate structural organization at this stage.

According to an embryology study, the main fish organs like the neural tube, optic vesicles, otic vesicles, head, and tail can be identified by 24 hours after fertilization (Kimmel et al. 1995). The rapidly developing embryo takes form as segmented muscles, nerves, rudimentary eyes, the circulatory system, and more emerge.


When organogenesis is complete, fully developed embryos hatch out of their protective chorions. Hatching occurs by enzymes breaking down the chorion, allowing the baby fish (fry) to emerge. Depending on the fish species, incubation periods until hatching can vary from one day to even weeks.

The tiny fry are extremely vulnerable immediately after hatching because they rely entirely on their egg yolk for early nourishment before they can actively hunt food (animals.mom.com). Their survival depends on their ecological habitat and availability of zooplankton to eat.

Spawning Behaviors in Fish

Broadcast Spawners

Broadcast spawning is a common reproductive strategy among marine fish like cod, haddock and plaice. The females release eggs into the water column, which then get externally fertilized by the males. This type of spawning behavior does not involve any parental care and usually takes place in large aggregations, with each female releasing tens of thousands of eggs.

The fertilized eggs are left adrift in the ocean currents.Since the eggs are unprotected, most get eaten by predators. But the sheer number of eggs produced helps ensure the survival of some offspring.

The newly hatched larvae, called ichthyoplankton, float around in the plankton until they mature into adult fish. Examples of broadcast spawners include eels, flounders, tuna and reef fish like wrasses and parrotfish.

Substrate Spawners

Many freshwater fish and some marine species are substrate or bottom spawners. The females lay eggs on surfaces like vegetation, rocks or gravel beds, which the male then fertilizes. Nest building and defending the breeding site are common parental behaviors in substrate spawning fish.

Some examples include sticklebacks, gobies and snakeheads. The male stickleback builds a nest with debris and plant matter where the female lays eggs. The male then keeps watch over the nest until the eggs hatch. Catfish and killifish bury their eggs in gravel or sand.

The male Killifish will aggressively defend the spawning site against intruders.

Since the eggs are deposited in a chosen nesting site instead of drifting in open water, the chances of survival are greater than broadcast spawning. The eggs also get fanned by the parent fish, helping ensure proper oxygenation.


Mouthbrooding or oral incubation is a unique reproduction method where the parents, either male or female, hold the eggs or fry in their mouths for protection. Common examples are the Cardinalfish and Cichlids. The female cichlid lays eggs in the breeding site, which are then fertilized by the male.

Once the eggs hatch, the female scoops up the fry in her mouth. She keeps them protected in her buccal cavity, not feeding herself, until the babies are ready to swim off on their own. Some cichlid species have the male fish incubate the eggs or young instead.

Since the developing eggs and fry are shielded inside the parent’s mouth, the survival rate is very high compared to other spawning strategies. However, the number of babies per brood is typically small, ranging from 10-60 fry.

Mouthbrooding provides maximum parental care and ensures propagation of the species.

Threats to Fish Eggs and Conservation

Habitat Loss

Fish rely on specific habitats for spawning and egg development. Unfortunately, over 50% of wetlands have been lost globally due to drainage for agriculture and coastal development. This destroys crucial nursery areas and egg deposition sites.

Studies show that the degradation and fragmentation of stream habitats alone can reduce fish egg survival by up to 50%. Protecting existing habitats through conservation efforts is vital.

Overfishing of Adults

Excess harvesting of mature adult fish severely impacts reproductive output. Overfishing adult populations to less than 20% of their unfished levels has been shown to significantly reduce number of eggs produced.

In fact, a global analysis found that better management of wild fisheries could increase egg production by over 200%. Sustainable fishing quotas and gear restrictions are needed to maintain healthy numbers of reproductive fish.

Pollution and Toxins

Surrounding water quality directly impacts egg development and larval survival. Studies demonstrate that common pollutants like heavy metals, pesticides, sedimentation, and pharmaceuticals can all lower hatching success and increase egg mortality. Oil spills are especially damaging.

Cleaner waters through pollution regulation and treatment infrastructures are essential for productive fish stocks.

Invasive Species

Non-native predators and competitors pose serious risks. For example, invasive crayfish species have devastated native fish eggs and larvae in many systems globally. Likewise, exotic aquatic plants can smother crucial spawning habitat.

Restricting transport and releases of known invasives plus monitoring for new threats can help prevent exposures.

Climate Change

Changing temperature, precipitation, and water chemistry trends threaten habitats supporting historic fish egg and larval development. High springtime runoff from shifting melt patterns may damage sensitive eggs during key stages. Acidification also impairs reproductive processes.

Identifying and protecting future resilient sites will enable fish persistence despite climate alterations.


In conclusion, fish eggs that will hatch into baby fish are referred to by several common names like fish roe, fish spawn, and caviar. There are various types of fish eggs suited to different species’ reproductive strategies. The eggs undergo a complex development process before hatching into larvae.

Understanding the terminology, characteristics, and biology of fish eggs provides insight into an important stage in the fish life cycle and how new generations of fish are produced.

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