What are the sources of vitamins, proteins and omega fats for vegetarians?

just asked a question about being a vegetarian, apparently fish isn't as good as i thought , and those huge nets hurt them, and they contain mercury and other stuff, i'm aiming at becoming a lacto-ovo vegetarian (which means I'll consume milk and eggs) And actually the milk i consume isn't sucked up by awful machines and i know the source of the milk we get, and the eggs are organic, I'll start gradually decreasing the amount of meat i consume, but what are the sources for proteins , i need a source for b12 vitamins and a source for the omega fats that exist in fish since i'm not gonna eat it at the last steps, I'm gonna start as a pescatarian till i get over my fish craving