Zebrafish (Danio rerio): care, feeding, and reproduction

The zebrafish (Danio rerio, previously known as Brachydanio rerio) is a small freshwater species native to South Asia. This fish is not only popular among aquarists for its resilience and ease of maintenance but has also become a key organism in scientific research due to its genetic similarity to humans.

Thanks to its rapid embryonic development, short life cycle, and regenerative abilities, the zebrafish has become an essential model in studies of genetics, neurobiology, and toxicology. Throughout this article, we will explore its characteristics, aquarium care, role in science, and much more.

Zebrafish: General Characteristics and Anatomy

Taxonomy

The zebrafish, Danio rerio, belongs to the family Cyprinidae, which includes other fish such as carp.

• Domain: Eukaryota
• Kingdom: Animalia
• Phylum: Chordata
• Class: Actinopterygii
• Order: Cypriniformes
• Family: Danionidae
• Subfamily: Danioninae
• Genus: Danio
• Species: Danio rerio (F. Hamilton, 1822)
• Synonyms: Cyprinus rerio, Brachydanio rerio, Cyprinus chapalio, Perilampus striatus, Danio lineatus, Brachydanio frankei, Danio horai
• Common names in Spanish: Pez cebra
• Common names in English: Zebrafish, zebra danio, Zebra, Striped danio, rerio.

The synonym Brachydanio frankei refers to the leopard zebrafish, which was once considered a separate species.

Physical Characteristics

The zebrafish (Danio rerio) has an elongated body with an average length of 3 to 5 cm, though some individuals can grow up to 6 cm under optimal conditions. Its most distinctive feature is the horizontal blue stripes running along its body, giving it the name “zebrafish.”

Ackroyd et al. (2025) reported that zebrafish are capable of rapid dynamic color changes, likely serving both as camouflage through background matching and as social signaling by enhancing the internal contrast of their stripes. The fish darken their overall coloration in dark environments and lighten in bright environments.

Zebrafish Anatomy

• Slim, elongated body with a rounded snout.
• Five dark blue horizontal stripes running from head to tail.
• Translucent fins without spines.
• Upward-facing mouth, adapted for surface feeding.
• Internal organs similar to those of higher vertebrates, making it an ideal model for biomedical research.

These fish are hardy and adapt well to various conditions, making them ideal for both beginner aquarists and scientists in research laboratories.

Types of Danio rerio and Differences from Other Species

There are several variants of D. rerio, including:

• Classic zebrafish → Blue with golden stripes.
• Leopard danio → Spotted pattern instead of stripes.
• Albino danio → Lacks pigmentation, with pink eyes.
• Fluorescent danio (GloFish) → Genetically modified with bright colors.

Each has unique characteristics, but all require similar care.

Natural Habitat of Danio rerio

The zebra danio is a small tropical fish native to rivers and streams in Southeast Asia, particularly in India, Bangladesh, Pakistan, Nepal, and Myanmar (Ge, 2018).

The natural habitat of D. rerio includes freshwater streams and rivers, especially in floodplain areas. It is often found in shallow, slow-moving waters near stream edges or in ditches (Markowski, 2011), as well as in canals, ponds, and lentic water bodies, including rice fields.

Zebrafish Life Cycle and Development

The zebrafish life cycle is fascinating due to its rapid embryonic development and relatively short lifespan.

Zebrafish Reproduction: Eggs and Larvae

Zebra danio reproduction is a fast and efficient process. They are oviparous, meaning they lay eggs at the bottom of the tank, where they are externally fertilized.

Rahman et al. (2024) suggest that maintaining a ratio of one male per three females and a temperature of 29°C optimizes zebrafish spawning success in laboratory settings. The courtship behavior involves multiple males chasing females.

The spawning process takes place on bare substrates or vegetation. In captivity, they prefer gravel substrates over silt. For ovulation and spawning to occur, the presence of a male is required, indicating a signaling mechanism that coordinates reproduction between sexes.

Zebrafish are asynchronous spawners, meaning they can spawn frequently under optimal conditions, even daily.

• Females lay between 100 and 300 eggs per spawning event.
• Eggs hatch in less than 48 hours, producing larvae about 3 mm long.
• In 5 days, larvae develop organs and begin free swimming.

Zebrafish developmental stages

Zebrafish Eggs

The reproduction of Brachydanio rerio begins with egg-laying. A female can lay 100 to 200 eggs per spawn. The eggs are fertilized externally and hatch in approximately 48–72 hours, depending on water temperature.

Zebrafish Embryos

Zebrafish embryos are transparent, allowing scientists to observe their development in real time. This transparency is one of the reasons why Danio rerio is so valuable in research.

Zebrafish Larvae

Newly hatched zebra danio larvae are small and initially rely on their yolk sac as a nutrient source. As they develop, they begin feeding independently and undergo fin formation and other external changes.

Pereira (2023) concluded that density may be an environmental factor influencing sex determination in D. rerio. The study observed that high density (30 fish per tank) appears to favor male development, while low density (10 and 5 fish per tank) seems to favor female development.

Lifespan

• In captivity, zebrafish live for 3 to 5 years.
• They begin reproducing at around 3 months of age.
• In the wild, lifespan may be shorter due to predators and environmental challenges.

Due to its rapid development, zebrafish are an ideal model for studying embryogenesis and vertebrate growth.

Zebrafish feeding: Diet and eating habits

The zebrafish is omnivorous and requires a balanced diet. Recommended foods include:

• High-quality flake or pellet food.
• Live or frozen foods such as Artemia (brine shrimp) and Daphnia (water fleas).
• Crushed vegetables like spinach or zucchini.

A well-balanced diet ensures healthy growth and vibrant colors. The amount of food should be 4% of the fish’s body weight per day (Avdesh et al., 2012). Experts recommend feeding only the amount that the fish can consume in 10 minutes.

Adatto et al. (2022) reported that while intensive feeding (higher amounts of rotifers and Artemia during the larval and juvenile stages) accelerates growth and time to first reproduction in D. rerio, it can also have negative effects on reproductive performance, particularly in embryo viability and fecundity.

On the other hand, Xi et al. (2023) determined that the maximum carbohydrate level in the adult zebrafish diet should be below 30%, as an excess of carbohydrates (30%–50%) caused hepatic steatosis (fatty liver disease). Similarly, Pacheco Mendes et al. (2024) reported that a high-calorie diet (Artemia cysts) is important for accelerating fish growth.

Printzi et al. (2021) highlighted the importance of carefully considering feeding practices, particularly the transition rate from live food (Artemia) to microdiets, to ensure normal skeletal development, proper growth, and high survival rates in Brachydanio rerio larvae.

Oregano extract (Origanum vulgare), especially at a 1% concentration in the diet, has significant potential to enhance growth, immunity, and resistance to bacterial infections in zebra danio (Rashidian et al., 2021).

Zebrafish Care in Aquariums

Zebrafish are hardy and easy to maintain. Despite generations of breeding in a laboratory environment, Lavery and Mason (2023) found that D. rerio retains innate preferences for environmental features that mimic its natural habitat, such as plants and gravel.

Table 1. Water Quality Requirements for Zebrafish (D. rerio) Care.

A well-maintained tank will ensure the health and longevity of the zebrafish.

Zebrafish Compatibility with Other Aquarium Fish

The zebrafish (D. rerio) is a peaceful and social fish, making it an excellent choice for community aquariums. However, it is important to carefully select tank mates to avoid aggression or stress.

The best tank mates for zebra danio are those that:

• Have a peaceful temperament
• Prefer to swim in schools
• Require similar water conditions

Table 2. Recommended Species to Keep with zebra danio (Danio rerio).

👉 Tip: Always keep at least 6 zebrafish together to prevent stress and aggression towards other fish.

Fish NOT Compatible with Danio rerio

Despite being peaceful, zebrafish can become very active and playful, which may stress calmer fish or those with long fins. It is also important to avoid aggressive species that might attack zebra danio.

Table 3. Fish Not Compatible with Danio rerio.

👉 Tip: Avoid any long-finned fish or those that prefer a calmer environment, as zebrafish may nip fins when kept in small groups or if they lack enough swimming space.

Diseases Affecting Danio rerio

Although they are hardy fish, zebrafish can be susceptible to certain diseases, such as Oodinium (velvet disease), microsporidiosis caused by Pseudoloma neurophilia, and various mycobacteria species.

Regular observation and maintaining good water conditions are key to preventing and detecting these diseases early.

Zebrafish in Scientific Research

According to Teame et al. (2019), thanks to its fully sequenced genome, easy genetic manipulation, high fecundity, external fertilization, rapid development, and nearly transparent embryo, zebra danio is a unique animal model for biomedical research, including the study of biological processes and human diseases.

Zebrafish offer several advantages over other vertebrate models used to study human diseases (Choi et al., 2021).

Main Research Areas Using Zebrafish

• Genetics and Developmental Biology → Used to study gene expression and its role in growth.
• Neurodegenerative Diseases → Key for Alzheimer’s and Parkinson’s research.
• Tissue Regeneration → Unlike humans, zebrafish can regenerate their spinal cord and organs.
• Cardiology → Its cardiovascular system is studied to understand human heart diseases.
• Cancer → Used to test drugs and analyze toxin responses.
• Toxicology → Zhao et al. (2024) reported that zebra danio provide a widely accepted model to study toxicological effects and mechanisms. These effects include behavioral, intestinal, cardiovascular, liver, endocrine, neurotoxic, immunotoxic, genotoxic, reproductive, and transgenerational toxicity.

For these reasons, zebrafish have become a key ally in modern medicine.

Conclusion

The zebrafish (D. rerio) is a fascinating species for both scientists and aquarium enthusiasts. Its beauty, resilience, and research value make it a unique and essential species in modern science.

If you are looking for an easy-to-care-for, energetic fish with a history in biomedical research, zebra danio is the perfect choice.

References

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Adatto I, Lawrence C, Krug L, Zon LI (2022) The effects of intensive feeding on reproductive performance in laboratory zebrafish (Danio rerio). PLoS ONE 17(11): e0278302. https://doi.org/10.1371/journal.pone.0278302

Avdesh, A., Chen, M., Martin-Iverson, M. T., Mondal, A., Ong, D., Rainey-Smith, S., Taddei, K., Lardelli, M., Groth, D. M., Verdile, G., Martins, R. N. Regular Care and Maintenance of a Zebrafish (Danio rerio) Laboratory: An Introduction. J. Vis. Exp. (69), e4196, doi:10.3791/4196 (2012).

Choi, T., Choi, T., Lee, Y., Choe, S., & Kim, C. (2021). Zebrafish as an animal model for biomedical research. Experimental & Molecular Medicine, 53(3), 310-317. https://doi.org/10.1038/s12276-021-00571-5

Ge, W. (2018). Zebrafish. Encyclopedia of Reproduction (Second Edition), 704-710. https://doi.org/10.1016/B978-0-12-809633-8.20618-3

Kütter, M. T., Barcellos, L. J. G., Boyle, R. T., Marins, L. F., & Silveira, T.. (2023). Good practices in the rearing and maintenance of zebrafish (Danio rerio) in Brazilian laboratories. Ciência Animal Brasileira, 24, e–74134. https://doi.org/10.1590/1809-6891v24e-74134E

Lavery, J. M., & Mason, G. J. (2023). Mirror, mirror on the wall… How tank material and the presence of “enrichments” affect competition and agonism in zebrafish (Danio rerio). Applied Animal Behaviour Science, 266, 106005. https://doi.org/10.1016/j.applanim.2023.106005

Markowski, D. 2011. “Danio rerio” (On-line), Animal Diversity Web. Accessed March 24, 2025 at

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Printzi, A., Kourkouta, C., Fragkoulis, S., Dimitriadi, A., Geladakis, G., Orfanakis, M., Mazurais, D., Zambonino-Infante, L., & Koumoundouros, G. (2021). Balancing between Artemia and microdiet usage for normal skeletal development in zebrafish (Danio rerio). Journal of Fish Diseases, 44(11), 1689-1696. https://doi.org/10.1111/jfd.13487

Rahman, U. O., Jaman, A., Sultana, Z., Rahman, M. H., Shahjahan, M., & Islam, M. S. (2024). Unlocking the secrets of successful spawning: laboratory techniques for breeding ornamental zebrafish Danio rerio (Hamilton, 1822). Aquaculture, Aquarium, Conservation & Legislation, 17(5), 1732-1748.

Rashidian, G., Boldaji, J. T., Rainis, S., Prokić, M. D., & Faggio, C. (2021). Oregano (Origanum vulgare) Extract Enhances Zebrafish (Danio rerio) Growth Performance, Serum and Mucus Innate Immune Responses and Resistance against Aeromonas hydrophila Challenge. Animals, 11(2), 299. https://doi.org/10.3390/ani11020299

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Xi, L., Lu, Q., Liu, Y., Gong, Y., Liu, H., Jin, J., Zhang, Z., Yang, Y., Zhu, X., Han, D., & Xie, S. (2023). Study on Carbohydrate Metabolism in Adult Zebrafish (Danio rerio). Aquaculture Nutrition, 2023(1), 1397508. https://doi.org/10.1155/2023/1397508

Zhao, W., Chen, Y., Hu, N., Long, D., & Cao, Y. (2024). The uses of zebrafish (Danio rerio) as an in vivo model for toxicological studies: A review based on bibliometrics. Ecotoxicology and Environmental Safety, 272, 116023. https://doi.org/10.1016/j.ecoenv.2024.116023