Zebrafish are so pretty

I was tinkering in the lab this morning, trying out a new gadget, collecting embryos, and cleaning and fine-tuning my microscope, when I saw this. Can you guess what I’m looking at?

Hints: shot at 40x, it’s not part of the embryo itself, and every zebrafish pro is thoroughly familiar with it.

There was a guess that it was yolk. No! I took a quick picture of the yolk sac in this same embryo, at the same magnification.

Those boulders at the top are cells, blastomeres. The bright band across the middle is the yolk syncytial layer, cells that bridge the gap between the cellular embryo and the yolk mass at the bottom. See? Nothing alike.

A few of you got it right, or came close: it’s the chorion.


  1. blf says

    A monster from the forthcoming Doctor Who episode provisionally titled Zebra Crossing, where people mysteriously vanish in crosswalks. They step into the crosswalk and are neither seen nor remembered, except in pictures and videos, ever again.

    The Doctor is baffled, and whilst the companion vanishes, the Doctor is unable to follow; there are hilarious scenes of the Doctor repeatedly doing an Abbey Road-style crossing, trying to also vanish.

    (No spoilers, so we skip a bit here…)
    The monster turns out to be an escapee from a mad biologist’s lab, a failed cross-breeding between a kraken and zebrafish, in an attempt to devise a biosolution to the ocean’s plastic pollution. However, it prefers making people, not plastic, vanish — and is purple.

    The picture is of the brain scouring pad used to wipe people’s memories of the vanished people. The Doctor successfully reverses the process — no neutron flows were involved — bringing almost everyone back and (…sorry, no spoilers!).

  2. emergence says

    Oh, someone already suggested the yolk. I’ll just guess that its part of the egg case then.

  3. Callinectes says

    I’m not sure, but I’m pretty certain that ~1% of it is derived from the cosmic background radiation.

  4. blf says

    Closeup of the unicorn of the sea, Millions of mysterious ‘sea pickles’ swamp US west coast:

    Huge and unexplained bloom has fishers racing to save their nets, and scientists hurrying to study the rare animal

    A rare, tiny marine creature known as the “unicorn of the sea” has swarmed in its millions on the west coast of America, ruining fishermen’s nets and baffling scientists who are scrambling to find out more about them.

    Fishers along the west coast have told researchers that in some places they are unable to catch anything because the pyrosome clusters are so dense and tightly packed. Their hooks, when pulled from the ocean, wriggle with the odd-looking creatures, which are sometimes referred to as “sea pickles” or “fire bodies”.

    The distinctive animals — only a few millimetres long — have washed up on popular beaches, bemusing local residents.

    Hilarie Sorensen, a graduate student at the University of Oregon who is part of a new research team set up to study the bloom, said: “Right now we are scrambling to learn as much as possible while we have the opportunity.”


    Pyrosomes are tubular, gelatinous creatures that are actually moving colonies of tiny organisms. Asexual creatures which reproduce by cloning themselves, they have long fascinated seafarers, who have been pictured swimming through the middle of pyrosomes up to 30 metres long.

    Sorenson said no one knows how much surface area the pyrosome bloom covers, except that they have gathered right along the west coast in mammoth clusters. She said every time she or fisherman had seen them the swarm stretched “as far as the eye can see”.


    This summer was the first time she saw a real-life pyrosome in her many years of marine study. Her mentor, Rick Brodeur, a research biologist at the National Oceanic and Atmospheric Administration’s north-west fisheries science center in Oregon, saw his first pyrosome only a couple of years ago, after a 30-year career in marine science.

    “On one of our cruises we saw 60,000 in five minutes and they were ripping apart our nets,” said Sorensen. “They were glowing and floating on the surface, completely covering the sea”

    Few marine scientists have seen pyrosomes in the flesh because during the day they stay in the depths, sometimes up to 700 metres under the surface and usually in the open sea.