The poet ends his poem with, "Notice Neptune, though,/ Taming a sea-horse, thought a rarity". What is this referring to?

The ending lines of the poem refer to the Roman god Neptune, who is known as the god of the sea. The "sea-horse" in this context could be a literal sea creature, or it could metaphorically represent something that is difficult to control or tame, such as the sea itself or even one's own emotions or desires. The phrase "thought a rarity" suggests that the act of taming the sea-horse, or overcoming this challenge, is considered a rare and noteworthy achievement. This could be a metaphor for the poet's own struggles and accomplishments. The specific interpretation may vary depending on the overall context and themes of the poem.