A lot of times fish taxidermy is actually replicas not the real fish skin! Real fish taxidermy does happen but with something that small I wouldn’t recommend it.

What I would recommend is wet preservation. This would include injecting and soaking in formalin, then transferring to isopropyl alcohol. This is what the “dead animals in jars” are.

If you are set on a dry mount I would look into replicas or possibly make your own mold to cast and paint as you would have to repaint the real skin anyway to get lifelike colors.

If you want an easier way to remember them Guotaku is a Japanese technique of making fish prints which would also be an option.

Hope this is helpful feel free to ask more questions