Gill or Branchia

Question

I am writing a dialog and I need to mention Gills (or Branchias), the respiratory organ of animals like fish.

I was wondering which one would be more common or casual in English speech (say, in the US), and if it's a commonly known word.

Thank you!

Answer 1

Most Americans who would understand that word (Branchia) would more likely associate it with a region of the (human/mammalian) body than with gills. It has to do with embryology from a time when fetuses appear to have gills, and the body parts formed therefrom.

Please note that in the lizard, tortoise, pig and human embryos, there is a stage in fetal development where all have what appear to be gills. It is called the Branchial Apparatus.

Where in a fish, these will become gills, in terrestrial animals, they do not. However they do go on to develop body parts with the word Branchia- still attached:

branchial cyst, branchial sinus, branchial fistula, etc.

therefore, in casual speech, if you are referring to fish branchia, use gills.

Answer 2

Unless one is writing dialog between rather specialized biologists, gills would be the better choice.