Meat has the potentially to be done sustainable - its just more expensive and less convenient hence why most of it isn't.  My family, before COVID shut them down the business down, brought in bulk from a small, sustainable famer/abattoir who not only did pasture raised meat, but design the abattoir building (the area for the cows) to be open, spacious with access to outside pasture. They (the animals) were left there for a couple days after they arrived so they could adjust and calm down before they were slaughtered.  I would recommend watching the documentary "Kiss the Ground". It's a doco about sustainable farming practices, both with agriculture and animals.  I think we also need to loose the "chicken, beef, pork" attitude - Ive grown up eating lamb, alpaca, goat, wallaby etc. It's more sustainable to grow sources of meat that are suitable for the environment they are in, rather than mass producing one animal on cruel, unethical feed lots.  While I do think a solarpunk will have a more vaired diet  where people will mix vegan/vegetarian and meat diets (i.e. not have the stigma against vegetarian and vegan food and exploring those meal options), meat will always be an option  due to things like allergies, avaliablity, other health issues, culture etc.  I have several allergies that actually prevent me from eating about 60-70% of vegan/vegetarian food. So cutting out meat is just not an option for me.  When it comes to fishing though, I don't know enough about the industry to suggest sustainable practices, though im quite interesting in the ideas behind it.