The world loves seafood. Even places that are nowhere close to the sea. Which would be fine if transporting seafood didn’t cause so many emissions. Don’t fear though, it’s possible to enjoy seafood in a sustainable fashion. The answer is simple, eat local!
Like many other food industries, driven in part by competition from from large corporations, smaller fisheries have banded together to create Community-supported fisheries. The food from these groups only travel about 65 km on average instead the thousands that corporate fish go before finally landing on an actual plate. Obviously, the smaller distance is better for emissions.
This means if you want fish, the best course of action is to ask what the local fish is and eat that. If you live somewhere that is not close to any sort of fishing option, then perhaps cutting down on fish in your diet and substituting for something more sustainable would be a better choice for you.