Question

Marine cartilaginous fishes overcome water loss to their environment by:

a. Storing urea in their body fluids, causing them to by hypertonic to sea water.
b. Producing very small quantities of urine
c. Drinking large quantities of fresh water
d. Having specialized chloride cells in their gills that prevent water loss

Which option is the best to answer the question?

Answer 1

The correct option is Option A - Storing urea in their body fluids, causing them to by hypertonic to sea water.

Unlike bony fishes which have specialised cells for removing salt from their system, cartilaginous fishes do not possess these cells. Instead, they rely upon osmoregulation, by increasing or decreasing solute concentration inside their body,

The most common strategy used by these fishes is to increase the concentration of urea in their body, such that the concentration is equal or more than the surrounding salt water. This ensures that water from inside the fish body does not flow outside to the environment.

These fihses absorb water through their gills, and excess salt is secreted via a specialised gland situated near the anus.