These little fish is called Chirimen Jako (ちりめんじゃこ). These little fish are semi-dried salted tiny sardines and they are calcium-packed! They are often called Chirimen Jako or Shirasu Boshi (しらす干し).
When they are boiled in salted water and not dried, they are called Kamaage Shirasu (釜揚げしらす). I looked up and found that you don’t need to rinse these before using them. When they are too salty, you can quickly rinse or pour hot water.
You can find them in a Japanese grocery stores.
Recipes Using Chirimen Jako
Cold Tofu (Hiyayakko) with Chirimen Jako.
Egg Tofu On Rice with Kamaage Shirasu.