This is perhaps one of the most disturbing lines in the poem. After becoming a sexless entity, devoid of humanity, femininity, and pleasure, the woman becomes nothing but a vessel for "pearling eggs", for birth. She has no voice against this utter oppression, coherent or otherwise, no ability to protest nor even the lungs to do so, being a fish. She is rendered little more than an automaton, who serves no other purpose besides producing unfertilized eggs. She is also alone in this endeavor; her eggs lie "in seaweed" and she requires no companion or mate for copulation, only the hope that her eggs will be fertilized and bear life, but that is the work of the male not the female. The woman cannot even fully perform her duties as a mother.
Here, "Screamlessly" is given its own line, a trend for most of the emotionally charged words and phrases in the poem. This emphasizes the despair and desperation in the term, especially as it separates the preceding and following line, which alone would form a full clause. It is not a grammatically necessary word, but a line that must be included for moral and emotional reasons.