Why do sharks produce urea instead of ammonia like most fish?

Sharks do not produce urea as their primary nitrogenous waste product, unlike most other fish. Sharks primarily excrete Trimethylamine N-oxide (TMAO) as their primary nitrogenous waste product.

While some sharks and fish species can produce small amounts of urea as a byproduct of their metabolism, it is not the primary form of nitrogenous waste they excrete. TMAO is a small organic molecule that is more soluble and less toxic than ammonia. It allows sharks to retain water and maintain a higher osmotic pressure in their body fluids, which is crucial for their survival in the marine environment.