Zebrafish - Reproduction

Reproduction

The approximate generation time for Danio rerio is three to four months. A male must be present for ovulation and spawning to occur. Females are able to spawn at intervals of two to three days, laying hundreds of eggs in each clutch. Upon release, embryonic development begins; absent 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. Development progresses rapidly – precursors to all major organs appear within 36 hours of fertilization, and hatching takes place 12–36 hours later, depending on the embryo's internal conditions and the external temperature, which is ideally 28.5 °C (83.3 °F). Swimming and feeding behavior begin about 36 hours later. The sex of juveniles cannot be distinguished except by dissection, and sex determinants are not clearly understood.

To encourage the fish to spawn, some researchers use a fish tank with a sliding bottom insert, which reduces the depth of the pool. The technique is most effective in the early morning, given that ovulation and spawning are enhanced by light. Researchers have been able to collect 10,000 embryos in 10 minutes using this method. 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.