Is there a way to slow down microcrustacea?

A couple days ago, I took a sample from one of my ecospheres to look at under the microscope. In some ways, it isn’t the best microscope – it is a cheap USB microscope, and while its imaging capability is okay, it is so unstable that turning the focus knob causes it to move its field of view.

Anyway, the reason I did this was to try to identify some very tiny crustaceans. At first, I had thought they were Daphnia, then speculated that they might be nauplii of the copepods, but I couldn’t see them well enough to be sure. After viewing them through the microscope, I believe they are ostracods; but I cannot be sure because they are averse to light and quickly move out of view. I was unable to get any pictures of them. There were also some even smaller things, that just looked like transparent ovals swimming in a helical path, and some kind of green oval swimming, smaller than the ostracods, but bigger than the transparent ovals.

The thing is, I don’t want to harm them just for the sake of a photo. I put all the samples back after the session was done. Is there a way to slow their movements enough for a photo without harming them? Please try to keep your suggestions low budget.

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On the microscope slide, suck away most of the water using a twist of tissue paper. That should immobilise them and they won’t desiccate so long as you don’t leave them like that for a long time.

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I would assume a spell in the fridge would slow them down, as it does for most poikilothermic organisms.

I think pinning them in place using pressure is the best approach. You can also add a tiny bit of petroleum jelly to the edges of the coverslip to slow it from drying out and get better control of how smashed it will be.

I have seen it suggested to add something to make the water more viscous, such as methylcellulose. But I have never bothered to try this even though I bought some just for this very purpose, so I can’t comment on how useful it would be.

You could also sift through your ecosphere for molted exoskeletons or already dead crustaceans. Dead things have many advantages.

I think club soda (carbonated water) is the way to go, check this paper. I vaguely remember a professor of mine that worked with copepods and water fleas recommending soda after collecting the samples. But you probably want to check if it has any negative effects

After you immobilize them using one of the suggested methods, turn off your lights and use a small flashlight from the side (at level of the specimen) to illuminate the specimen. It really improves the contrast.

I saw this reference. https://www.mccrone.com/mm/narcotizing-slowing-down-and-preserving-microscopic-and-other-aquatic-animals/

Thanks for that great link. It mentioned Epson Salts which I do remember using on marine inverts - easy to come by. Not sure if it would work for the purposes of the OP though.