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Are roe (fish eggs, caviar, etc.) single cells?

I have tried looking this up on google (sadly, to no avail), and I am guessing they might be multicellular (like bird eggs) or consist of one cell plus corona cells, or indeed unicellular.

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    $\begingroup$ I was under the impression that bird eggs (unfertilized or immediately after fertilization) were unicellular. $\endgroup$ – C_Z_ May 17 '15 at 17:07
  • $\begingroup$ I always assumed, that the yolk sack consisted of lots of other cells which are responsible for repositing all the nutrients. Otherwise all of that would just have to be secreted by cells outside of the egg somehow? But now that I actually looked it up, I was unable to find any reliable info on that either :-/ $\endgroup$ – TheChymera May 17 '15 at 18:29
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    $\begingroup$ Be careful not to confuse "egg" (the macroscopic structure) with "ovum" (the haploid cell). The vast majority of a bird's egg--even the yolk--is external to the ovum. (The wikipedia entry on yolk gets this wrong, by the way, based on a citation to a 65 year old embryology text). $\endgroup$ – Corvus May 18 '15 at 2:32
  • $\begingroup$ @Corvus Do you have an actual citation? A similar question on Reddit had the opposite answer, backed by a link to a dev bio textbook. I would not personally upvote the Quora answer were it posted here. $\endgroup$ – March Ho May 18 '15 at 5:58
  • $\begingroup$ @TheChymera Related question from here at BioSE on egg anatomy: Why are hard boiled eggs so homogeneous? $\endgroup$ – fileunderwater May 18 '15 at 11:15
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Yes; the first division starts at around 45min post fertilization in zebrafish. This picture is stuck in every zebrafish lab.

   enter image description here

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If the fish eggs are unfertilised, then they are single celled (but in the haploid state - a state with half of a full set of DNA for an organism). However, if it is fertilised it will only remain in the single celled stage for approximately 45 minutes (depending on species (in this case I'm using the zebra fish). After that 45 minute period the cell begins to divide.

What actually makes caviar so expensive is that (according to most websites I've found) it actually is an unfertilised egg collected from a Sturgeon. There seem to be a few different ways that caviar is extracted. Extracting the ovaries after stunning the fish (which is explained on Science: How Stuff Works - and gives more information on caviar), more or less giving the fish a Caesarian section, and the final way that I noticed was called "stripping" which is a non-sergical way using an ultrasound.

The News Article on the ultrasound procedure of collecting the roe suggested that it wasn't yielding good results.

So, caviar is actually a single haploid cell.

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  • $\begingroup$ Do you have a source for your claim? Also, did you mean "Caesarian section"? $\endgroup$ – March Ho Jun 1 '15 at 17:22

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