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. (Boisen, et al., 2003; Engeszer, et al., 2007; Mayden, et al., 2007; Spence, et al., 2008)
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. (Albertson and Kocher, 2006; Mayden, et al., 2007; Spence, et al., 2008)
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. (Spence, et al., 2008)
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. (Engeszer, et al., 2007; Spence, et al., 2008)
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. (Engeszer, et al., 2007; Spence, et al., 2008)
Adult zebrafish provide no parental care to young. Zebrafish are independent immediately upon hatching. (Spence, et al., 2008)
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. (Gerhard, et al., 2002; Spence, et al., 2008)
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. (Engeszer, et al., 2007; Grant and Kramer, 1992; Spence, et al., 2008)
There is no information available regarding the average home range size of zebrafish.
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. (Cermakian and Sassone-Corsi, 2002; Spence, et al., 2008)
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. (Engeszer, et al., 2007; Spence, et al., 2008)
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. (Engeszer, et al., 2007; Spence, et al., 2008)
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. (Engeszer, et al., 2007)
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. (Boisen, et al., 2003; Briggs, 2002; Engeszer, et al., 2007; Mayden, et al., 2007)
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. (Boisen, et al., 2003; Briggs, 2002; Engeszer, et al., 2007; Mayden, et al., 2007)
There are no known adverse effects of Danio rerio on humans
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.
Danny Markowski (author), The College of New Jersey, Matthew Wund (editor), The College of New Jersey, John Berini (editor), Animal Diversity Web Staff.
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
living in the southern part of the New World. In other words, Central and South America.
living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.
uses sound to communicate
living in landscapes dominated by human agriculture.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
uses smells or other chemicals to communicate
having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.
ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
fertilization takes place outside the female's body
union of egg and spermatozoan
a method of feeding where small food particles are filtered from the surrounding water by various mechanisms. Used mainly by aquatic invertebrates, especially plankton, but also by baleen whales.
mainly lives in water that is not salty.
having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.
ovulation is stimulated by the act of copulation (does not occur spontaneously)
referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
having the capacity to move from one place to another.
specialized for swimming
the area in which the animal is naturally found, the region in which it is endemic.
an animal that mainly eats all kinds of things, including plants and animals
found in the oriental region of the world. In other words, India and southeast Asia.
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
the business of buying and selling animals for people to keep in their homes as pets.
chemicals released into air or water that are detected by and responded to by other animals of the same species
photosynthetic or plant constituent of plankton; mainly unicellular algae. (Compare to zooplankton.)
an animal that mainly eats plankton
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
condition of hermaphroditic animals (and plants) in which the female organs and their products appear before the male organs and their products
breeding is confined to a particular season
reproduction that includes combining the genetic contribution of two individuals, a male and a female
associates with others of its species; forms social groups.
uses touch to communicate
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
uses sight to communicate
animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)
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