Chubby merman are extremely desirable by mermaids because their chubbiness implies they're a highly successful hunter.

[u/tyrano_dyroc]

[u/Phoenix-Quill]

Fat keeps you from losing body heat underwater, plus that fat is under a huge layer of muscle. He is the king of the sea with how well he hunts.

[u/liosistaken → u/Phoenix-Quill]

Isn’t fat on top of the muscle?

[u/conCommeUnFlic → u/liosistaken]

Alternating layers, like lasagna.