> In the stores fish and meat are different aisles.

This does not change the fact that fish is still, in fact, meat.

> And the discussion is about carbon footprint, not veganism.

Broadly, but not in this context.

Fishing is the primary source of plastic in the ocean, it has its environmental issues as well. That is before we talk about offshore fish farms, where the fish live in a cage their whole life, get fed subpar inputs, and generally resembles chicken farms. Not to mention that we have over fished the natural ocean to the point that the salmon food chain is in danger of collapse...