In order to perform a more balanced form of processes inside the mammals body or as whole system there is always the requirement for having a more specific form of mechanism called as the homeostasis.
This process is required to attain a very balanced state of solutes and other liquids inside the body system of the humans. As, to have this position the mammals have certain secretions like the release of antidiuretic hormone (ADH) from the pituitary gland. Which, acts on the nephrons present inside the kidneys and directs it to absorb more amount of water and solutes, in order to prevent any more water loss.
So, basically the secretion is done for avoiding any water and solute losses from the mammals body system in any form. Which would also result in a more balanced form of blood pressure and as a whole a more balanced form of water volume inside the body.
The body of a fish is streamlined because, it increase the speed of the fish in the water. The more the streamlined shapes more easier for the fish to swim in the water.
