You need to follow standard procedure, such as this one:

https://research.jcu.edu.au/archive/enabling/aac/cairns-aac/biological-sample-preparation-for-the-sem

Try to find ESEM (Environmental SEM).

Thank u @imaddisher but they have to do it here in the college and we don't have any ESEM. But thank you for the tip, I will suggest to them!

You need to follow standard procedure, such as this one:

https://research.jcu.edu.au/archive/enabling/aac/cairns-aac/biological-sample-preparation-for-the-sem

Hey @Vladimir thank youuu for the this, we already received the frog dehydrated and in our lab we don't have the equipment for CDP and also we don't have the HMDS solution too.

So to avoid the dryness, we store the frog on little bottle with glycerin and se how it goes. Also, we are thinking about observing the sample in low vacuum instead of coating. What do you think?

If your frog is already dehydrated (means air dried?), you can/must do nothing. Specimen is already damaged and "prepared" for SEM observatiion. Just keep it in desiccator to avoid rehydration. As for low vacuum - you can try it. Sometimes sputter coating can damage some very fragile specimens, but I doubt yours qualifies as "very fragile". But why not to try?

No, the frog was dehydrated on alcohol solution. Thank u for the help @Vladimir

 I will try LV first instead of coating. The only thing is that my SEM on LV only works with BSE and in biological samples I always use lower Accv.

Also, do you know what is the best way to choose the chamber pressure on lv mode? I've already read some articles and even the user guide of the microscope, but I still a little bit confuse how to choose the correct chamber pressure. May you help me with that @Vladimir? Thank you

For LV - BSE it is better to use the lowest pressure possible. Decrease pressure until you see charging effects, than back up a little. Actual value of pressure is microscope- and specimen-dependent.

Okay. Got it, I asked you about the pressure because my SEM you can set from 10 to 650 Pa.

I think I will start around 50 Pa

A buffered fixative such as glutaraldehyde or osmium tetroxide should help in retaining the structures and features of the sample in question and would preserve the sample identity.

The environmental scanning electron microscope (ESEM) with good conditions (HV, temperature and pressure) allows you to make good observations without any preparation.

@Vladimir May u help me one last time? I always sputter non conductive samples, but the equipment has an option to etch mode. What is the difference between etch and sputter? Thanks

If your SEM can operate between 10 and 650 Pa, then that's plenty of hydration for the sample. I can condense water onto a sample at 500 Pa, but I used a cold stage too. Operating in BSE mode is fine. It isn't clear to me whether your sample is already dry before characterization.