do mexican salamanders mainly breathe by enternal gills

Yes, Mexican salamanders, or axolotls, primarily breathe through their external gills throughout their lifetime. However, it's important to understand the nuances of their respiratory system:

1. External Gills: In their larval stage and even when they mature, axolotls maintain these feathery, filamentous structures behind their heads. These are the key organs for extracting oxygen from the water and expelling carbon dioxide.

2. Internal Gills: As they mature, axolotls also develop internal gills, which are less conspicuous but still functional. These internal gills, located internally near the pharyngeal region, can supplement gas exchange in adults.

3. Skin Respiration: Additionally, like many amphibians, axolotls have permeable skin that allows for cutaneous respiration, or "breathing" through the skin. This is especially useful if the external gills are not fully functional or if the animal is in a low-oxygen environment.

4. Adaptability: Axolotls' ability to use multiple respiratory mechanisms is a testament to their adaptability and underscores the importance of their gills as primary respiratory organs while being complemented by their skin and internal gills.

While the external gills are the most recognizable and significant for respiration, the overall respiratory system of an axolotl is designed to optimize gas exchange in their aquatic environment. This combination allows them to sustain their life processes effectively underwater.