Humans, plants and most animals must consume freshwater to live. For humans, the water cannot have a salt concentration greater than 2-percent, or the body will expel a greater amount of fluids which could lead to severe dehydration or even death.
An aquatic animal is either a vertebrate or invertebrate, and lives in the water for most or all its life. Aquatic animals may breathe air or extract oxygen that is dissolved in water through specialized organs called gills, or directly through their skin. The number of aquatic species on planet earth is still unknown.
Some Questions Asked, and Answers About Aquatic Animals Are:
Q. If all life requires drinking water, what do marine aquatics do?
A. Marine aquatic animals drink water constantly! To survive they have adapted to their marine environment by creating a balance between the water’s salinity and the salt present in their own bodies.
Simple organisms such as anemones, sponges and sea urchins have equal amounts of saline in their bodies to that found in the surrounding water. Teleosts however, have a concentration of salt in their bodies that is lower than that existing in the water. These fish drink water to regulate their salt levels and to avoid dehydration, a completely normal phenomenon whereby they lose water through the skin. This process called osmosis serves to retain adsorbed salts when drinking. Leftover salts are secreted through cells present in their gills. The complete process is regulated by a structure present in their kidneys, known as the renal corpuscle, which is responsible for performing necessary filtration.
Q. Do freshwater fish drink water?
A. Like marine fish, freshwater fish also drink water, but in noticeably smaller quantities, and have a higher concentration of salts in their bodies than their environment. When these fish drink water, it forces a loss of salt from the body. To control this, they use two mechanisms: the first is found on the outside of the body, whereby the scales and mucous substance that covers the organism limits the access of water. The second is in the kidneys, since these organs process excess water and expel it in large quantities, but in lower salt concentrations. Freshwater fish are among the animals that urinate the most.
Q. Do fish urinate?
A. Urinating is a normal and essential function in all animals. The amounts and concentrations of the elements expelled will vary according to the species and the characteristics of the water in which they live.
Note: Teleosts are the largest infraclass of fish, characterized for having bone vertebrae, a tail, scales and a swim bladder (gas bladder). Most fish species belong to the Teleost infraclass.