From http://www.treehugger.com/green-food/meat-eaters-guide-get-to-know-the-carbon-footprint-of-your-diet-lamb-beef-cheese-are-the-worst.html we have
which I find pretty fascinating — certainly I would have put pork much closer to beef than either salmon or Turkey... really interesting stuff. I'd like to see as well the same graph but per calorie rather ...
A study of canned mackerel and herring shows that the production of the aluminium can is responsible for most of the products carbon footprint (Buchspies et al. 2011). Impacts associated to transport are slightly smaller compared to frozen codfish. Storage of frozen fish obviously requires more energy than storage of canned products, however it doesn't seem ...
Here in The Netherlands we have the 'Viswijzer' (link is to Dutch version only).
It is an index where you can lookup which types of fish you can buy just fine and which types you should not buy because they are endangered and/or not caught sustainably. I'm not sure about the exact criteria they have but according to this index:
The first thing you want to do is read up on the varieties of fish. Some fish like goldfish, are purely domesticated. Some other fish pose rare problems (neon tetras for example). There are other fish where wild caught fish are possibly being sustainably harvested but tank-bred fish are more popular (cardinal tetras).
There are no clear standards in ...
In this TED talk Marcel Dicke mentions that from 10kg of feed you will get:
1kg of beef or,
3kg of pork or,
5kg of chicken or,
9kg of locusts
I believe that he talks about locusts emitting less greenhouse gases as well.
You can see the chart at about 9:30 into the talk. The whole talk is quite good.
Please eat tuna only from the cans with MSC (Marine Stewardship Council) label, avoid pizzas or sandwiches that cannot provide such certification. (See the approved answer of @THelper (and the comments) for more details, this is the short answer!)
Why not simply get a food waste composter with earthworms? This allows worms for fish food, a place to make use of food waste, it gives valuable organic liquid and solid fertilizers that can be used for wheat grass or other edible plants. The water from the fish tanks are used to water the plants, and the plant system is used to filter and clean the fish ...
In north america we have Seachoice.org. They make a handy pocket guide. Yellowfin tuna is on the red (bad) list. But they say canned Albacore is ok.