How Do Goldfish Have Babies {A Step by Step Guide}

Have you just noticed that your goldfish has just laid some eggs?

Do you know what you need to do next?

Well don’t worry as I will cover the whole process here and you will learn everything you need to know.

How Do Goldfish Reproduce?

Goldfish reproduction follows a process known as spawning, where males and females come together to fertilize eggs. Goldfish exhibit sexual dimorphism, which means there are distinct physical differences between males and females.

Male goldfish, often called “males,” possess tubercles or breeding stars on their gill covers and pectoral fins during the breeding season. These small white or pinkish bumps aid in gripping the female during courtship. Females, on the other hand, have a plumper and more rounded body shape compared to males.

How Do Goldfish Have Babies

Reproductive Organs of Goldfish

Goldfish, like other fish, possess specific reproductive organs that play a crucial role in their reproductive processes. Let’s explore the reproductive organs of goldfish in more detail:


Goldfish have paired gonads, which are the primary reproductive organs responsible for producing gametes (sex cells). In females, the gonads are ovaries, while in males, they are testes. The gonads develop and mature during the breeding season when the fish are ready to reproduce.


Female goldfish have two ovaries, one on each side of their body. The ovaries are responsible for producing eggs, or ova, which are released during spawning. The eggs are typically small and spherical, and multiple eggs are produced by each ovary.


Male goldfish have two testes, one on each side of their body. The testes produce sperm, or milt, which is released during spawning to fertilize the eggs. The testes consist of lobes that contain seminiferous tubules, where sperm cells are produced.


Once the eggs are released from the ovaries, they travel through the oviducts in the female goldfish. Oviducts are muscular tubes that connect the ovaries to the urogenital opening. The eggs move through the oviducts, where fertilization can occur if milt is present.

Urogenital Opening

The urogenital opening is a common opening found in both male and female goldfish. It serves as the exit point for the reproductive and waste products. During spawning, the eggs are released through the female’s urogenital opening, while the male releases milt through the same opening.

When Is the Breeding Season for Goldfish

The breeding season for goldfish typically occurs during the spring and summer months. The exact timing of the breeding season can vary depending on several factors, including the specific breed of goldfish and the prevailing environmental conditions.

One of the primary triggers for goldfish to enter their breeding mode is an increase in water temperature. As the temperatures rise during the spring months, it signals to the goldfish that it’s time to engage in reproductive behavior. In general, goldfish prefer water temperatures between 68°F (20°C) and 74°F (23°C) for breeding.

Another crucial factor influencing the breeding season is the length of daylight hours. As the days become longer and the amount of daylight increases, it serves as a natural cue for goldfish to initiate their breeding activities.

The extended daylight hours in spring and early summer mimic the natural breeding conditions that goldfish experience in their native habitats.

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Factors That Trigger Breeding Behavior

Several factors can trigger breeding behavior in goldfish. These factors help stimulate the reproductive instincts of the fish and signal that it is the appropriate time to engage in breeding activities. Here are some key factors that can trigger breeding behavior in goldfish:

Water Temperature

Goldfish are ectothermic creatures, meaning their body temperature is regulated by the surrounding environment. An increase in water temperature, usually in the range of 68°F (20°C) to 74°F (23°C), serves as a significant trigger for initiating breeding behavior. Warmer water temperatures during the spring and summer months mimic the natural conditions in which goldfish breed in the wild.

Daylight Length

The lengthening of daylight hours as spring approaches and progresses is another crucial trigger for goldfish breeding. Longer daylight periods serve as a natural cue for goldfish to prepare for reproduction. The increase in daylight triggers hormonal changes in the fish, influencing their reproductive readiness and aggressive behavior.

Seasonal Changes

Changes in the overall environment, such as the transition from winter to spring, can also play a role in triggering breeding behavior. Goldfish are sensitive to environmental cues, including changes in water chemistry, air pressure, and natural rhythms. These seasonal changes can stimulate their breeding instincts.

Social Interaction

The presence of other goldfish, both males and females, can stimulate breeding behavior. Males may exhibit courtship behaviors, such as chasing and nudging females, to initiate the breeding process. The visual cues and interactions between males and females can trigger hormonal responses that lead to reproductive behavior.

Spawning Sites

Availability and suitability of spawning sites can also trigger breeding behavior. Goldfish prefer areas with vegetation, plants, or objects like rocks or spawning mops to deposit their eggs. The presence of suitable spawning sites can encourage goldfish to engage in courtship behavior and initiate the spawning process.

How Do Goldfish Eggs Get Fertilized

Goldfish eggs are fertilized externally. During the breeding season, when a female goldfish is ready to release her eggs, she will lay them in the water. Simultaneously, the male goldfish will release milt, which contains sperm, into the water. The milt and eggs mix together, allowing for fertilization to occur.

When the male goldfish releases the milt, it contains millions of sperm cells. The sperm cells are equipped with long tails called flagella, which allow them to swim freely in the water. The released milt disperses in the water, surrounding the eggs.

Goldfish Eggs Get Fertilized
some goldfish eggs before they were fertilized

As the eggs are released by the female, they are covered in a protective gelatinous coating. This coating helps keep the eggs intact and provides some level of protection against predators and external factors.

When the milt comes into contact with the eggs, the sperm cells start swimming towards the eggs using their flagella. Once a sperm cell reaches an egg, it attaches to the surface of the egg and penetrates the egg membrane.

The genetic material from the sperm, containing the male’s DNA, fuses with the genetic material in the egg, which carries the female’s DNA. This fusion of genetic material is known as fertilization.

Egg Development Stages

The development of goldfish eggs can be divided into several stages, each marked by distinct changes and transformations. Here are the common stages of goldfish egg development:


The first stage occurs when the male goldfish releases milt containing sperm into the water and the female goldfish releases her eggs. The sperm cells swim towards the eggs, and upon contact, one sperm cell fertilizes each egg. Fertilization is the fusion of genetic material from the sperm and egg, initiating the development process.


After fertilization, the zygote undergoes rapid cell division through a process called cleavage. The fertilized egg divides into smaller cells, forming a solid mass of cells. This stage establishes the basic structure and sets the foundation for subsequent development.

Blastula Formation

As the cell division continues, the mass of cells begins to hollow out, forming a blastula. The blastula consists of a fluid-filled cavity surrounded by a single layer of cells. This stage marks the transition from a solid mass of cells to a hollow structure.


During gastrulation, the blastula undergoes a complex process of cell movement and differentiation. The cells rearrange and migrate, forming three primary germ layers: ectoderm, mesoderm, and endoderm. These layers give rise to various tissues and organs of the developing goldfish.


Organogenesis is the stage where the major organs and structures of the goldfish start to form. The cells within the germ layers differentiate further to develop specific organs, such as the heart, gills, nervous system, and digestive system. The embryo begins to take on a recognizable fish-like shape.

Eye and Pigmentation Development

As the goldfish embryo develops, the eyes become more distinct, and pigmentation starts to appear. The pigments contribute to the coloration of the fish and become more pronounced as the development progresses.


Near the end of the development process, the embryo develops an operculum, which is a protective structure covering the gills. The fully developed embryo then hatches from the egg, emerging as a free-swimming larva, known as fry.

How Goldfish Select a Suitable Spawning Site

Goldfish exhibit a natural instinct to select suitable spawning sites for depositing their eggs. The choice of a spawning site is crucial for the successful development and survival of the eggs. Here are some factors that influence how goldfish select a suitable spawning site:

Vegetation and Plants

Goldfish often prefer spawning sites with vegetation, such as water plants or submerged aquatic plants. These plants provide a sense of security and protection for the eggs. The fine leaves and stems of the plants offer a surface for the eggs to attach to, preventing them from sinking or being swept away by water currents.


Goldfish may also choose spawning sites with suitable substrates. Gravel, rocks, or even artificial spawning mops are commonly used as substrate choices. The rough surface of these materials allows the eggs to adhere and provides stability.


Goldfish tend to choose spawning sites that are relatively shallow compared to the rest of the water body. Shallow areas provide better exposure to sunlight, which helps in the development of the eggs. Additionally, shallower waters can offer better oxygenation and nutrient circulation, which benefits the developing eggs.

Privacy and Security

Goldfish prefer spawning sites that offer some level of privacy and security. Areas with hiding spots, such as dense vegetation or structures like rocks and caves, provide protection against potential predators. The presence of suitable hiding places allows the goldfish to feel more secure and increases the chances of successful spawning.

Water Flow

Goldfish generally prefer areas with moderate water flow for spawning. Strong currents can dislodge the eggs or prevent proper attachment, while stagnant areas may lack adequate oxygen and nutrient supply. Therefore, selecting sites with suitable water flow is important for successful egg development.


Goldfish are known to prefer well-lit areas for spawning. Adequate lighting stimulates the natural spawning instincts of goldfish and supports the growth and development of the eggs. Areas with sufficient natural or artificial light sources are more likely to be selected as suitable spawning sites.

It’s important to provide a variety of potential spawning sites within the goldfish tank or pond to cater to their preferences. This can be achieved by incorporating live plants, artificial spawning mops, rocks, and other suitable structures. Offering a range of options allows goldfish to choose their preferred site, leading to more successful spawning and egg development.

Goldfish Spawning Site
An example of a good spawning site for goldfish

Incubation Period

The incubation period is a critical stage in the development of goldfish eggs, where they undergo transformation and grow into fry. Here’s an overview of the incubation process for goldfish eggs:

Egg Attachment

After fertilization, the goldfish eggs are typically attached to a suitable substrate, such as aquatic plants, rocks, or gravel. The gelatinous coating surrounding the eggs helps them adhere to the chosen surface. It’s important to ensure that the spawning site provides stability and protection for the attached eggs.

Environmental Conditions

Creating and maintaining optimal environmental conditions during the incubation period is crucial. The water temperature should be within the appropriate range for goldfish, typically around 68-74°F (20-23°C), to support proper development.

Water quality parameters, such as pH, ammonia, and nitrite levels, should be closely monitored and maintained at suitable levels to prevent any harmful effects on the developing embryos.

Embryo Development

Over the course of the incubation period, the fertilized eggs undergo various stages of development. The embryos develop from a single cell into more complex structures. As the cells divide, the embryos grow in size, and the eyes and other features become visible.

The time it takes for the eggs to develop into fry varies depending on factors like water temperature and goldfish breed, but it usually ranges from a few days to a couple of weeks.

Oxygenation and Water Flow

Proper oxygenation is crucial during the incubation period. Adequate water flow and aeration help ensure a sufficient oxygen supply for the developing embryos. This can be achieved through the use of air stones, water pumps, or filtration systems. Maintaining proper water flow also helps prevent the buildup of waste or debris around the eggs, which can potentially harm their development.

Protection and Monitoring

Throughout the incubation period, it’s important to protect the developing eggs from potential threats. This includes keeping the water free from predators, such as adult goldfish or other fish species, as well as maintaining stable water conditions. Regular monitoring of the eggs allows for early detection of any issues or abnormalities, enabling timely intervention if necessary.


As the incubation period nears its end, the embryos will start to show signs of readiness for hatching. The eyes of the fry become more pronounced, and they may become more active within the eggs.

Eventually, the fry will start to emerge from their eggs, using specialized structures called an operculum to break through the egg membrane. Once fully hatched, the fry will typically carry a yolk sac, which provides them with nutrients for their initial survival.

The Early Stages of Fry Development

The early stages of fry development in goldfish are crucial as they undergo rapid growth and transformation. Here’s an overview of the early stages of fry development:

Yolk Sac Absorption

After hatching, goldfish fry have a small yolk sac attached to their bellies. The yolk sac contains essential nutrients that sustain the fry during their early development. Over time, the fry gradually absorb and utilize the nutrients from the yolk sac. It’s important to note that during this stage, the fry should not be fed as they rely on the yolk sac for their nutrition.

Free-Swimming Stage

Once the fry have absorbed the yolk sac, they enter the free-swimming stage. They become more active and start exploring their environment. At this stage, the fry should be provided with a suitable tank or pond with ample space for swimming and proper filtration to maintain water quality.

Fry Food

As the fry transition from the yolk sac dependency, they need to be fed appropriate fry food. Specialized fry food, either in the form of commercial fry pellets or finely crushed flakes, should be provided. These foods are formulated to meet the nutritional needs of growing fry and promote healthy development.

Water Quality

Maintaining optimal water quality is crucial during the early stages of fry development. Regular water changes, filtration, and monitoring of water parameters such as ammonia, nitrite, and nitrate levels are necessary to ensure a clean and healthy environment for the fry. Poor water quality can lead to stress, illness, and stunted growth.

Growth and Development

During the early stages of development, goldfish fry experience rapid growth. Their bodies elongate, fins develop and become more defined, and their coloration starts to emerge. The rate of growth may vary depending on factors such as genetics, nutrition, and water conditions. Providing a balanced and nutritious diet, along with suitable environmental conditions, promotes healthy growth and development.

Separation and Size

As the fry grow, they will gradually increase in size. At some point, it may become necessary to separate the fry into individual tanks or larger spaces to prevent overcrowding and competition for resources. This allows each fry to have sufficient space and resources for optimal growth.

Gradual Introduction to Adult Food

As the fry continue to mature, they can be gradually introduced to adult goldfish food. This transition can be done by slowly incorporating small amounts of crushed or powdered adult food into their diet. It’s important to monitor their response to the new food and adjust accordingly.

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Factors Influencing the Growth Rate and Size of the Fry

The growth rate and size of goldfish fry can be influenced by various factors. Understanding these factors can help ensure optimal growth and development. Here are some key factors that can influence the growth rate and size of goldfish fry:

Genetic Factors

The genetic makeup of the fry plays a significant role in their growth potential. Different goldfish breeds and strains have varying growth rates and potential adult sizes. Some breeds are known for their rapid growth, while others may grow at a slower pace. It’s important to consider the genetic characteristics of the parent fish when assessing the growth potential of the fry.


Providing proper nutrition is crucial for the healthy growth of goldfish fry. High-quality and nutrient-rich fry food should be offered regularly. The food should contain essential proteins, fats, carbohydrates, vitamins, and minerals necessary for their growth and development. Overfeeding or underfeeding can negatively impact their growth, so it’s important to monitor their feeding habits and adjust the amount accordingly.

Water Quality

Maintaining optimal water quality is essential for the growth and well-being of goldfish fry. Poor water quality, including high levels of ammonia, nitrite, or nitrate, can hinder growth and cause stress or illness. Regular water changes, appropriate filtration, and monitoring of water parameters are necessary to ensure a clean and healthy environment for the fry.


The water temperature can affect the metabolic rate and growth rate of goldfish fry. Maintaining a suitable temperature range, typically around 68-74°F (20-23°C), promotes healthy growth. Extreme temperature fluctuations or prolonged exposure to temperatures outside the optimal range can negatively impact their growth and overall health.

Space and Tank Size

Providing adequate space for goldfish fry is important for their growth. Overcrowding can lead to increased stress, hinder growth, and even result in stunted development. A larger tank or pond allows the fry to swim freely, encourages exercise, and provides ample space for growth.

Water Parameters

Apart from water quality, other water parameters can also influence the growth of goldfish fry. Factors such as pH levels, hardness, and oxygen levels should be within suitable ranges. Sudden changes in water parameters should be avoided, as they can cause stress and impact growth.

Stress Levels

Minimizing stress is crucial for the healthy growth of goldfish fry. Stressors such as aggressive tankmates, sudden movements, loud noises, or excessive handling should be minimized. Stress can inhibit appetite, weaken the immune system, and slow down growth.


Hello, I'm Jason. I'm the guy behind I volunteer at my local fish shop and I created this site to offer tips and advice on the fish I care for.