Editing Zebrafish (section)

== Reproduction ==
[[File:Zebrafish Developmental Stages.tiff|thumb|upright=1.2|Stages of zebrafish development. Photos to scale except adult, which is about {{convert|2.5|cm|in|abbr=on|0}} long.]]

The approximate [[generation time]] for ''Danio rerio'' is three months. A male must be present for [[ovulation]] and [[spawning]] to occur. Zebrafish are asynchronous spawners<ref>{{cite journal |vauthors=Selman K, Wallace RA, Sarka A, Qi X |title=Stages of oocyte development in the zebrafish, Brachydanio rerio |journal=Journal of Morphology |volume=218 |issue=2 |pages=203–224 |date=November 1993 |pmid=29865471 |doi=10.1002/jmor.1052180209 |s2cid=46930941}}</ref> and under optimal conditions (such as food availability and favorable water parameters) can spawn successfully frequently, even on a daily basis.<ref>{{cite journal |vauthors=Aleström P, D'Angelo L, Midtlyng PJ, Schorderet DF, Schulte-Merker S, Sohm F, Warner S |title=Zebrafish: Housing and husbandry recommendations |journal=Laboratory Animals |volume=54 |issue=3 |pages=213–224 |date=June 2020 |pmid=31510859 |pmc=7301644 |doi=10.1177/0023677219869037}}</ref> Females are able to spawn at intervals of two to three days, laying hundreds of eggs in each [[clutch (eggs)|clutch]]. Upon release, embryonic development begins; in absence of sperm, growth stops after the first few cell divisions. Fertilized eggs almost immediately become transparent, a characteristic that makes ''D. rerio'' a convenient research [[model species]].<ref name=beec>{{cite journal |vauthors=Spence R, Gerlach G, Lawrence C, Smith C |title=The behaviour and ecology of the zebrafish, Danio rerio |journal=Biological Reviews of the Cambridge Philosophical Society |volume=83 |issue=1 |pages=13–34 |date=February 2008 |pmid=18093234 |doi=10.1111/j.1469-185X.2007.00030.x |hdl-access=free |s2cid=18044956 |hdl=2381/27758}}</ref> Sex determination of common laboratory strains was shown to be a complex genetic trait, rather than to follow a simple ZW or XY system.<ref name="pmid21949597">{{cite journal |vauthors=Bradley K, Breyer P, Melville D, Broman K, Knapik E, Smith JR |title=A SNP-Based Linkage Map for Zebrafish Reveals Sex Determination Loci |journal=G3 (Bethesda) |volume=1 |issue=1 |pages=3–9 |date=Jun 2011 |pmid=21949597 |pmc=3178105 |doi=10.1534/g3.111.000190 |s2cid=11161125}}</ref>

The zebrafish embryo develops rapidly, with precursors to all major organs appearing within 36 hours of fertilization. The embryo begins as a yolk with a single enormous cell on top (see image, 0 h panel), which divides into two (0.75 h panel) and continues dividing until there are thousands of small cells (3.25 h panel). The cells then migrate down the sides of the yolk (8 h panel) and begin forming a head and tail (16 h panel). The tail then grows and separates from the body (24 h panel). The yolk shrinks over time because the fish uses it for food as it matures during the first few days (72 h panel). After a few months, the adult fish reaches reproductive maturity (bottom panel).

To encourage the fish to spawn, some researchers use a fish tank with a sliding bottom insert, which reduces the depth of the pool to simulate the shore of a river. Zebrafish spawn best in the morning due to their [[Circadian rhythms]]. Researchers have been able to collect 10,000 embryos in 10 minutes using this method.<ref name=Spawning2012/> In particular, one pair of adult fish is capable of laying 200–300 eggs in one morning in approximately 5 to 10 at time.<ref name="Hill 6–19">{{cite journal |vauthors=Hill AJ, Teraoka H, Heideman W, Peterson RE |title=Zebrafish as a model vertebrate for investigating chemical toxicity |journal=Toxicological Sciences |volume=86 |issue=1 |pages=6–19 |date=July 2005 |pmid=15703261 |doi=10.1093/toxsci/kfi110 |doi-access=free}}</ref> Male zebrafish are furthermore known to respond to more pronounced markings on females, i.e., "good stripes", but in a group, males will mate with whichever females they can find. What attracts females is not currently understood. The presence of plants, even plastic plants, also apparently encourages spawning.<ref name=Spawning2012>{{Cite news |last=Dockser |first=Amy |name-list-style=vanc |url=https://www.wsj.com/articles/SB10001424052970203436904577154962232874998 |title=Birds Do It, Bees Do It, Even Zebrafish Do It—Just Too Little |newspaper=Wall Street Journal |date=January 13, 2012 |access-date=February 11, 2012 |archive-date=January 15, 2021 |archive-url=https://web.archive.org/web/20210115185526/https://www.wsj.com/articles/SB10001424052970203436904577154962232874998 |url-status=live}}</ref>

Exposure to environmentally relevant concentrations of [[diisononyl phthalate]] (DINP), commonly used in a large variety of plastic items, disrupt the [[endocannabinoid system]] and thereby affect reproduction in a sex-specific manner.<ref>{{cite journal |vauthors=Forner-Piquer I, Santangeli S, Maradonna F, Rabbito A, Piscitelli F, Habibi HR, Di Marzo V, Carnevali O |display-authors=6 |title=Disruption of the gonadal endocannabinoid system in zebrafish exposed to diisononyl phthalate |journal=Environmental Pollution |volume=241 |pages=1–8 |date=October 2018 |pmid=29793103 |doi=10.1016/j.envpol.2018.05.007 |bibcode=2018EPoll.241....1F |s2cid=44120848}}</ref>