I was taking to some clients about why it is that we can feel that male koi get rougher around their gill covers and along their bodies. I remarked that I studied sections under the microscope, comparing male to female koi.
Normally, fish have living epithelial cells right up to the surface; unlike us, who have skin cells that form keratinised dead cell layers. But in the male koi, they seem to produce bits on their skin surface that appear like keratin on histology sections. I concluded that this is the reason that males are rough.
One of them remarked, “But fish have carotene, it gives them their colour and that’s what we feed them.”
And so we began our lesson in spelling and pronunciation.
“Ke-ra-tin”, not “ka-ro-teeeeen”.