This refers to the younger man in the relationship. The term implies he is being "fed" or taken care of by the older woman, much like a pet or a smaller creature in a larger pond.
The term "Anak Ikan" is linguistically fascinating. It implies: datin cari anak ikan
Content creators often use the phrase as a title or theme for comedic skits. The Scenario: This refers to the younger man in the relationship