Fish contains all the essential amino acids we need in order to live. However, death may result if we only eat fish and nothing else. The reason for this is that fish doesn't have Vitamin C which is vital for humans to survive. Even at present, we use a couple of lemon drops when we eat cooked fish. The fish that eats plankton is the only one that contains Vitamin C but the sole way to extract it properly is to eat it raw including its intestines.