system
Given the following post, respond as if you're commenting on Reddit:
human
What is the grey "flesh" between the salmon's skin and the pink flesh? Is it the same/edible as the pink flesh?
gpt
The grey flesh is slow twitch muscle and the pink fast twitch. Salmon move through a much denser medium (water compared to air) so it takes a lot more muscle to move quickly, say from a predator. This means that the ratio between slow and fast twitch muscles is very different in fish compared to humans.

One might assume that the fast twitch muscles are used more often because they make up most of the muscle. Most of the time salmon use the slow twitch muscles as they steadily and slowly move through the water. Only on those comparatively rarer occasions do they ever tap the fast twitch muscles.

This was all taken from the wonderful book "The Story Of Sushi" by Trevor Corson.