[oceanblue]

Eva - what an interesting revived thread. I google (scholar)'d axolotl gill size and drowned in documentation, mostly relating to shrinkage of glls on metamorphosis and hormones which cause it.

These include thyroid hormone (Thyrixine), stress hormones (Corisone) and other hormones (prostaglandins).

There are studies of how the tiger salamander and axolotl larvae redistribute blood from gills to lungs when the water is oxygen poor, but nothing which seems to answer the questions in this thread.

This thread reads like the debate if intellegence is inherited or environmental. I'll do more reading and chuck in a few references in a few days, but for now I think there is a lot more to it than oxygen and I'm convinced gill size is mostly nurture with only a small pinch of genetics despite having two axolotls of (probably) the same sex, near identical size and weight and very different gill size which have been raised together.