Even more teeny than tobiko is masago, which is the roe of the capelin fish. Capelin is a type of smelt found in Arctic waters. Their roe is very small and orange in color, and is a popular addition to sushi.
Capelin is a sustainable fish found in large quantities, so eating masago sushi is an ocean-friendly option. Iceland is the world's largest producer of capelin roe, and their fishery practices are environmentally friendly.
Masago is sometimes mixed with wasabi and marketed as wasabi caviar.
(Image: Kathryn Hill)