Every now and then when I collect eggs, I notice on day two that some will be clumping together, which makes it hard to sort and separate them. When I look at them under the microscope it looks like little fibrous strings holding them together, and they really clump up. Sometimes all of the embryos in the dish will just end up in one pile that I have to pick apart one by one. The strings also glow under fluorescent light. Has anyone else had a similar problem? Does anyone know what this is?
It sounds like you are seeing water mold (or possibly a fungus) growing in your dish. These are common organisms in any aquarium and will start to grow rapidly in an optimal condition like an embryo plate. When you collect embryos, rinse them well to remove any tank debris and make sure to remove any dead embryos as soon as possible as these are perfect substrates and food sources for molds. Then I would recommend either methylene blue or embryo bleaching.
A concentration of 0.1% methylene blue in your embryo medium will inhibit the growth of mold. How long you treat them with it is up to you. A quick dose of 15-20 minutes will knock back molds, but they may or may not come back. Or you can keep them in it longer, all the way until hatch if you want.
Your other option is embryo bleaching. For this, you use diluted household bleach (i.e., sodium hypochlorite) to sterilize the surface of the embryos. There are a few protocols out there, just google "zebrafish embryo bleaching" and you will find them easily. Basically, you will put the embryos in a sieve (we use a tea strainer or small square of mesh) and take them through a series of bleach dips and water rinses. It is important to note that this process will harden the chorion, making it difficult for the embryos to hatch. So make sure that the protocol you select includes a procedure that uses pronase to help with the hatching.
I hope that helps and good luck with your embryos.
- Melissa
I think the clumping is caused by the fungus growing on your media. This can be caused by a lack of cleanliness when moving from a spawning tank to a rearing tank.
When collecting eggs you can use "egg water" media to anticipate the growth of fungi or microbes. Usually, I make the media with 1000 mL of water + 1.5 mL of salt stock + 2 drops of methylene blue.
I hope this helps.
Just add some methylene blue to your eggs (1 drop of saturated methylene blue solution to 100ml of water is a good starting point).
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