Often confused with tobiko, masago is similar in color and size. A trained eye will notice that masago eggs are just a tiny bit smaller than tobiko. The taste also gives it away—the fish eggs aren’t as crunchy as tobiko, and they are slightly more bitter.
Masago comes from the capelin, a fish that is part of the smelt family. Many sushi restaurants often use masago in place of tobiko (or try to pass it off as tobiko) because it is much less expensive than the flying fish roe. However, both tobiko and masago are mainly relegated to garnishes in upscale Japanese and sushi restaurants. In fact, they are not often sold on their own, whereas Ikura (salmon roe) is considered as higher-end fish roe.