Animal products cause cancer and heart disease, and that includes fish. Animal protein is implicated in increases in IGF-1 levels which are directly responsible for aging changes in cells and cancer. Even without the fat on board, like "lean protein," animal products carry too much protein to be healthy.
Eat a plant based diet after you're done with your fast. Beans, grains, veggies, fruits, and a few nuts and seeds. Low fat whole plant food diets are healing, animal diets are harmful.