Danio rerio

Geographic Range

Danio rerio is native to inland streams and rivers of India. Its has a broad geographic range in the Indian subcontinent, ranging from the Ganges and Brahmaputra river basins of Bangladesh, India, and Nepal. A few introduced populations of the species inhabit inland waters in the United States (California, Connecticut, Florida and New Mexico) and Columbia, South America.

• Biogeographic Regions
• nearctic nearctic
  • introduced introduced
• palearctic palearctic
  • native native
• oriental oriental
  • native native
• neotropical neotropical
  • introduced introduced

Habitat

Zebrafish live in freshwater streams and rivers but are more often considered floodplain species. They are most often found in shallow, slow-moving water near the edge of streams or in ditches. Because of monsoon season in their native geographic range, zebrafish have adapted to a broad range of temperatures, from 6 degrees C during winter to 38 degrees C in summer. Rice cultivation by humans has had a significant impact on zebrafish habitat. Rice farming requires damming of waterways and creation of irrigation systems. Since rice farming is common in India, many natural habitats of zebrafish have been dramatically altered by damming and irrigation. Fortunately, zebrafish are relatively tolerant of human disturbance and are able to survive and reproduce well in altered habitats.

• Habitat Regions
• temperate temperate
• tropical tropical
• freshwater freshwater

• Aquatic Biomes
• rivers and streams

• Other Habitat Features
• agricultural agricultural

Physical Description

Zebrafish have fusiform, laterally compressed bodies that reach an average length of 25 mm. The largest recorded zebrafish reached 64 mm in captivity. They have centrally located eyes and thin elongate mandibles with a protrusive lower jaw that causes the mouth to point upwards. Like other cyprinids , zebrafish are stomachless and toothless. As a result, they rely on gill rakers to break up food. Additionally, they are obligate suction feeders. Zebrafish have several defining features including an incomplete lateral line, two pairs of barbels, and several (usually 5 to 7) longitudinal stripes along the sides of their body. The degree of sexual dimorphism in zebrafish is minimal, as males tend to have more yellow coloration and tend to have larger anal fins than females.

• Other Physical Features
• ectothermic ectothermic
• heterothermic heterothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• male more colorful
• sexes shaped differently

Development

Immediately after hatching, all zebrafish develop into females. Once they become five to seven weeks old, gonadal differentiation begin to occur, Males take approximately 3 months to fully develop their testes. Sex determination is not fully understood; however, evidence suggests that food supply and growth rates play a key role in sex determination as slow-growing individuals become males and fast-growing individuals become females.

Reproduction

Zebrafish are promiscuous and breed seasonally during monsoon season. Mating behavior is also heavily influenced by photoperiod, as spawning begins immediately at first light during breeding season and continues for about an hour. In order to initiate courtship about 3 to 7 males chase females and try to lead female towards a spawning site by nudging her and/or swimming around her in a tight circle or figure eight. Spawning sites consists of bare substrate that tends to be well vegetated. In captivity, gravel spawning sites are preferred to silt spawning sites. In the wild, zebrafish breed in silt-bottomed habitats. When a breeding pair reaches the spawning site, the male aligns his genital pore with the female's and begins to quiver, which causes the female to release her eggs and the male to release his sperm. The female releases 5 to 20 eggs at a time. This cycle repeats for about an hour. While the presence of female pheromones is required for initiation of courtship behavior in the male, male gonadal pheromones are required by the female for ovulation to occur. There is limited evidence for male-male competition and female mate preference.

• Mating System
• polygynandrous (promiscuous) polygynandrous (promiscuous)

Zebrafish breed seasonally during the monsoons, which occur from April to August. Spawning has also been recorded outside wet season, suggesting that breeding may be seasonal as a result of food availability. They tend to breed in silt-bottomed and well vegetated pools. Zebrafish lay non-adhesive eggs without preparing a nest, and are considered to be group spawners and egg scatterers. Although time to hatching depends on water temperature, most eggs hatch between 48 and 72 hours after fertilization. Chorion thickness and embryo activity also impact incubation time. Zebrafish are approximately 3 mm upon hatching and are immediately independent. They are able to swim, feed, and exhibit active avoidance behaviors within 72 hours of fertilization.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• sequential hermaphrodite
  • protogynous protogynous
• sexual sexual
• induced ovulation induced ovulation
• fertilization fertilization
  • external external
• broadcast (group) spawning
• oviparous oviparous

Adult zebrafish provide no parental care to young. Zebrafish are independent immediately upon hatching.

• Parental Investment
• no parental involvement

Lifespan/Longevity

In the wild, most zebrafish live to be one year old. In captivity, zebrafish have a mean lifespan of 42 months. The maximum age observed in captivity was 66 months. Captive zebrafish develop spinal curvature after their second year, which is not observed in natural populations.

Behavior

Zebrafish are active, social, and diurnal. Shoaling appears to be innate in this species and social hierarchies are established by both males and females. Dominance is established via aggressive behavior, which includes biting and chasing. Dominant individuals establish mating territories near spawning sites and monopolize food resources.

• Key Behaviors
• natatorial natatorial
• diurnal diurnal
• motile motile
• social social
• dominance hierarchies dominance hierarchies

Home Range

There is no information available regarding the average home range size of zebrafish.

Communication and Perception

Olfaction, vision, and motion detection via the lateral line system help zebrafish perceive their local environment and evade potential predators. Movement in the surrounding water is detected by the lateral line, which can detect small changes in pressure in the immediate environment. Zebrafish respond to a broad range of chemical cues detected by the olfactory bulb. Olfaction is particularly important for reproduction in zebrafish. Female zebrafish must come in contact with male gonadal pheromones in order to ovulate. Meanwhile, male zebrafish must come in contact with female pheromones in order to initiate spawning behavior.

• Communication Channels
• chemical chemical

• Other Communication Modes
• pheromones pheromones

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

Zebrafish are omnivores. They get most of their food from the water column, mainly eating zooplankton and aquatic insects . Zebrafish also surface feed, eating terrestrial insects and arachnids . Zebrafish commonly eat mosquito larvae.

• Primary Diet
• omnivore omnivore
• planktivore planktivore

• Animal Foods
• eggs
• insects
• terrestrial non-insect arthropods
• zooplankton zooplankton

• Plant Foods
• algae
• phytoplankton phytoplankton

• Foraging Behavior
• filter-feeding filter-feeding

Predation

The main predators of zebrafish are snakeheads and freshwater garfish . Other predators include catfish , knifefish , spiny eels , Indian pond heron , and common kingfisher . Zebrafish show alarm in response to visual and olfactory predatorial cues. Anti-predator behavior is also triggered by injury pheromones. Alarm behaviors include increased agitation, aggression, and decreased feeding rates. Zebrafish have three pigment cell types that contribute to their stripes. One of the pigment cells, dark blue melanophores, can be altered in response to stimuli. This is believed to help zebrafish evade potential predators.

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

Zebrafish consume a number of insect species, including mosquito larvae. As a result, they likely help control insect pests throughout their geographic range. In addition, zebrafish are prey for a number of different piscivorous fish and bird species. There is no information available regarding parasites of this species.

Economic Importance for Humans: Positive

In 1981, George Streisinger and his colleagues began to use zebrafish as a model organism for research. Since then, they have become a popular model organism for biomedical research. Zebrafish primarily have been used to study vertebrate development, evolution, genetics, and disease. Zebrafish are popular as pets and genetically modified, glow-in-the-dark zebrafish have been developed for the aquaria trade as well.

Zebrafish have many attributes that make it a popular model organism for biomedical research. They are small, have a short generation time, and are easy to raise in captivity. Additionally, in comparison to other vertebrates, zebrafish produce a large number of eggs per mating event. Zebrafish undergo external fertilization which allows all stages of development to be easily observed and manipulated. Zebrafish embryos are transparent, making them particularly useful for developmental and embryological research.

• Positive Impacts
• pet trade pet trade
• research and education

Economic Importance for Humans: Negative

There are no known adverse effects of Danio rerio on humans

Conservation Status

Zebrafish have a broad geographic range and are locally abundant. They breed easily in their native habitat and in 2007, increasing catch rates suggested increasing abundance. Other than potential over exploitation for the aquaria trade, there are no known threats to the long-term persistence of this species. Zebrafish are classified as a species of least concern on the IUCN's Red List of Threatened Species.

Additional Links

Encyclopedia of Life

Contributors

Danny Markowski (author), The College of New Jersey, Matthew Wund (editor), The College of New Jersey, John Berini (editor), Animal Diversity Web Staff.

References

Albertson, R., T. Kocher. 2006. Genetic and developmental basis of cichlid trophic diversity. Heredity , 97: 211-221.

Boisen, A., J. Amstrup, I. Novak, M. Grosell. 2003. Sodium and chloride transport in soft water and hard water acclimated zebrafish (Danio rerio). Biochimica et Biophysica Acta , 1618: 207-218.

Briggs, J. 2002. The zebrafish: a new model organism for integrative physiology. American Journal of Physiology: Regulatory, Integrative and Comparative Physiology , 282 (1): R3-R9.

Cermakian, N., P. Sassone-Corsi. 2002. Environmental stimulus perception and control of circadian clocks. Current Opinion in Neurobiology , 12 (4): 359-365.

Engeszer, R., L. Patterson, A. Rao, D. Parichy. 2007. Zebrafish in the Wild: A Review of Natural History and New Notes from the Field. Zebrafish , 4: 21-40.

Gerhard, G., E. Kauffman, X. Wang, R. Stewart, J. Moore, C. Kasales, E. Demidenko, K. Cheng. 2002. Life spans and senescent phenotypes of zebrafish (Danio rerio). Experimental Gerontology , 37: 1055-1068.

Grant, J., D. Kramer. 1992. Temporal clumping of food arrival reduces its monopolization and defence by zebrafish, Brachydanio rerio. Animal Behaviour , 44 (1): 101-110.

Mayden, R., K. Tang, K. Conway, J. Freyhof, S. Chamberlain, M. Haskins, L. Schneider, M. Sudkamp, R. Wood, M. Agnew, A. Bufalino, Z. Sulaiman, M. Miya, K. Saitoh, S. He. 2007. Phylogenetic Relationships of Danio Within the Order Cypriniformes: A Framework for Comparative and Evolutionary Studies of a Model Species. Journal of Experimental Zoology Part B: Molecular and Developmental Evolution , 5: 642-654.

Nico, L., P. Fuller. 2009. "Brachydanio rerio" (On-line). USGS Nonindigenous Aquatic Species Database. Accessed March 31, 2011 at http://nas.er.usgs.gov/queries/FactSheet.aspx?speciesID=505 .

Spence, R., G. Gerlach, C. Lawrence, C. Smith. 2008. The behaviour and ecology of the zebrafish, Danio rerio. Biological Reviews , 83: 13-34.

Westerfield, M. 1995. The zebrafish book : a guide for the laboratory use of zebrafish (Danio rerio) . Eugene, OR: M. Westerfield, [c1995].