It is just like English sayings and phrases, there are Japanese sayings and phrases as well. It is called [kotowaza ことわざ].
海老で鯛を釣る Ebi de tai o tsuru
Few words for you.
Ebi – a shrimp
Tai – sea bream
A crow imitating a cormorant.
use small fry to catch (a) big fish
Fishing for sea bream (an expensive fish) with a little shrimp.
Getting a big thing with a small thing