The opening verses of the song had indicated that the singer's mother was a mermaid. Mermaids are human from the waste up and fish from the waist down. No part of them is seaweed. Fish don't have hair, so neither would the fish portion of a mermaid. And any hair on her human portion (including her head, which is most likely meant here) would be human hair. So it is nonsensical to imply that a mermaid would have "seaweed hair".

This song is in general perhaps the most underrated song on their "Brothers Four Greatest Hits" album. But the lyrics, especially in the second of the stanzas quoted above, wax a bit nonsensical. While "lonesome hands" is literally nonsensical, that can be reckoned to a figure of speech called synecdoche, where a part of something is mentioned to reference the whole. So it really means they were lonesome, not just their hands. But the problem comes in when we ask why they were lonesome in spite of holding hands. It is especially incongruous how the last two lines above make it seem that their lonesome state in holding hands was the reason for crying "Come Back To Me". And if they were lonesome even when holding hands, that kind of belies the qualifier "Now" in the previous verse that says "NOW I am lonely". The "lonesome hands" of the latter verse makes it seem they were lonesome all along. That sort of answers the question "Why did we have to part?" in the first stanza above, doesn't it?

No doubt the part about "jumpin' as high as the sky" is meant as hyperbole, but even with a hyperbole, one needs to pick a fitting subject of one's hyperbole, or nonsense can result rather than a successful hyperbole. And catfish are just out of place in this attempt. They are a negatively-buoyant type of fish, meaning they sink to the bottom when they aren't actively expending energy to keep themselves afloat. They are bottom feeders. They don't leave the surface of the water like some fish do. If flying fish (which don't truly fly but glide above the water's surface for remarkable distances) had been the subject of choice for the hyperbole, it might have worked. It also might have worked with types of fish that sometimes jump above the water's surface to catch a flying insect above the water. But to make the claim for a bottom-feeding fish such as catfish results in nonsense rather than successful hyperbole. If one said that oysters flew out of the water and soared up to serenade the gulls, that would just be nonsense, rather than a successful hyperbole. It is essentially as nonsensical to imply that bottom-feeding fish would jump up out of the water. This song has a quirkily appealing melody to an unusual degree, while the tone of its lyrics is generally melancholy. But in this line the songwriters pretty much "lost it", with nonsense that makes a mockery of the song's overall mood.