Seafood in general tends to be high in B vitamins. Fish is no exception. Mackerel in particular has over 300% DV of vitamin B12 in a single 100 gram serving. For reference, 100 grams is about a decent sized handful. Eat fish as a snack or side and you’ll be well on your way to getting your daily dose. Fish is better for more than B vitamins. Fish also contains lots of protein and omega 3 fatty acids!