Dear Bhuvanesh,

At 3 days postfertilization.

For further details, please see the section "Potential advantages of zebrafish as a model for studying DILI " in the publication contained in the following link entitled "Zebrafish as model organisms for studying drug-induced liver injury ".

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4219854/

Hoping this will be helpful,

Rafik

Dear Bhuvanesh

The zebrafish (Danio rerio) is a tropical freshwater fish belonging to the minnow family (Cyprinidae ) of the order Cypriniformes. Native to the Himalayan region , it is a popular aquarium fish , frequently sold under the trade name zebra danio.The zebrafish is also an important and widely used vertebrate model organism in scientific research, and was the first vertebrate to be cloned It is particularly notable for its regenerative abilities and has been modified by researchers to produce several transgenic strains. The National Institutes of Health website Clinicaltrials.gov estimates there are more than 48 million Americans currently enrolled in clinical or observational studies.

Zebrafish are omnivorous, primarily eating zooplankton, phytoplankton, insects and insect larvae, although they can eat a variety of other foods, such as worms and small crustaceans, if their preferred food sources are not readily available.

Zebrafish have the ability to regenerate their fins, skin, heart, lateral line hair cells, and, during their larval stages, brain. In 2011, the British Heart Foundation ran an advertising campaign publicising its intention to study the applicability of this ability to humans, stating that it aimed to raise £50 million in research funding.

Zebrafish are especially well suited for forward genetic analysis of developmental processes due to their external fertilization, embryonic size, rapid ontogeny, and optical clarity – a constellation of traits that enable the direct observation of events ranging from gastrulation to organogenesis with a basic stereomicroscope. Further, zebrafish embryos can survive for several days in the haploid state. The production of haploid embryos in vitro is a powerful tool for mutational analysis, as it enables the identification of recessive mutant alleles present in first generation (F1) female carriers following mutagenesis in the parental (P) generation.

Zebrafish eggs are fertilized externally, permitting access to the zygote from the onset of fertilization

there are several limitations and drawbacks to the use of haploids. First, haploid zebrafish embryos live for only several days, and typically die between 3 and 5 days post fertilization Haploid zebrafish embryos can be distinguished from diploids based on several characteristics, foremost among them being a short and stocky body that nevertheless has the normal number of somite segments.

At this point there will be approximately 800 µl of UV inactivated sperm for haploid clutch fertilization. The sperm should be kept on ice throughout the entire duration of time spent on squeezing females. Sperm in cold Hank’s can be used for up to 6 hr without any reduction in fertilization outcome. Interestingly, other researchers have reported that sperm in cold Hank’s is viable from several hours to several days. The approximate generation time for Danio rerio is three months. The approximate generation time for Danio rerio is three 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. Pool the sperm from several males in ice-cold, full-strength Hank's saline. Sperm from 5-10 males is adequate for fertilization of several hundred eggs. Sperm in cold Hanks's will continue to fertilize eggs efficiently for up to 90 minutes. "Eyeball" the concentration of sperm, collecting enough to make a cloudy suspension.It nis also observed fertilization when nonactivated sperm were injected into activated eggs. In addition, the eggs had a limited time period (1 h or less) during which fertilization was possible after collection.

The zebrafish embryo develops rapidly, with precursors to all major organs appearing within 36 hours of fertilization. A mouse might have a litter of 10 offspring that spend three weeks in the womb. A zebrafish will lay 100-500 eggs every week, and once fertilized, the eggs waste no time. The first cell division in the embryo occurs within 45 minutes of fertilization, so scientists can observe the effect of adding or deleting genes at the one-cell stage.

regards,

Prem Baboo

http://www.jove.com/science-education/5151/zebrafish-reproduction-and-development

https://zfin.org/zf_info/zfbook/chapt7/7.52.html

https://zfin.org/zf_info/zfbook/chapt2/2.8.html

Hi, 

It really depends on what you want to study, when you decide to induce a drug treatment. If you need to observe changes in the 1 cell stage (i.e. via microinjection) you must administer it within 30 minutes of fertilization. If you want the larvae to orally ingest it, you need to wait between 5-7 day post fertilization (when the yolk has been consumed and they begin swimming to 'hunt' for food). If you want to see the effect of a drug on a specific phenotype or disease, you need to wait until that phenotype or disease develops. If you can give a little more info about your project, we may be able to give you more specific advice. 

Thanks!