The device known as shoyu-tai (or soy-sauce snapper in Japanese) was invented in 1954 by Teruo Watanabe, the founder of Osaka-based company Asahi Sogyo, according to a report from Japan’s Radio Kansai.
It was then common for glass and ceramic containers to be used but the advent of cheap industrial plastics allowed the creation of a small polyethylene container in the shape of a fish, officially named the “Lunch Charm”.
The invention quickly spread around Japan and eventually worldwide, and it is estimated that billions have been produced.
If it breaks down into tiny pieces its not biodegradable. The definition of biodegradable is that its chemically “processed by nature”.
BTW, biodegradable does not necessarily mean innocuous. A lot of “natural” elements and compounds are toxic. Something may be biodegraded, and leave mercury as one of the resulting elements, for example.