I wonder if they were inspired by the story of Hanuman's son Makardhwaja. In the Indian/subcontinental sources, his mother was an actual fish who was impregnated by Hanuman's sweat (or 'seed') that fell into the sea. But if you go a little further to Southeast Asia, the mother becomes Suvannamaccha, the golden mermaid. Of course in those versions Hanuman isn't a celibate and has an actual affair that produces offspring. Perhaps the DKDM creatives were inspired by these stories and incorporated aspects of them into the Jalandhara story. Hence Mahadev's energy falls into the ocean and impregnates a mermaid, producing his son Jalandhara.
And yes, Jalandhar's story has certain Oedipal aspects just like Andhaka (though the parallels are far more explicit in the latter case).