I don't dispute that fish is nutritious - but so is corn and most all other foods that we eat.  Its just that you don't have to eat it.  My (high) horse would also be nutritious for that matter.  My point is why recommend fish (or horse) when you can get all the nutrition you need from plants, and no sea turtles, whales or sharks get killed in the process.  I can get the same Omega-3 from my flaxseeds, hemp hearts, chia seeds and so many other sources.  So I have to take a B12 supplement - no big deal as far as I am concerned.  Lots of non-vegans are B12 deficient as well.