Here in the UK we have a long tradition of eating Soft Herring Roes aka Herring Milts - I.e. sperm sacks. I eat about 3 ounces two or three times a week, lightly fried in butter and with a squeeze of lemon, served with spinach and potato as a breakfast or lunch dish.
I haven't been ably to find any nutritional info but they are traditionally regarded as highly nutritious. I'm sure they must be high in O3's, zinc, and lots of other goodies!