Obviously a full vegan diet is the greenest, but I can't do it.
But if you are at least aware of the insane cost for the planet of fishing (regardless of farmed/non farmed) and raising animals (beef especially) I invite you to try to limit your intake. Maybe by eating less of it you can also afford to also raise the quality.
fish/beef > pork > lamb/mutton > > poultry > cheese > eggs > vegetables
If every time you eat you're at least aware of this scale, you may decide to switch some of your meals. Hamburger? Maybe eat some pulled pork. Pulled pork? You can replace it with lamb. Etc, etc down to vegetables. And if you really want that hamburger, enjoy it without any guilt!
Do what you want, but know that changing your diet habits and sharing this information with others will have a more positive impact than buying an electric car (which will put some hundreds tons of CO2 in the atmosphere during production alone)