On planet earth, water occupies 71-percent of the surface, with continents and islands on the remaining 29-percent. Of the water mass, 96.5-percent is salt water in the oceans; 3.5-percent is freshwater located in lakes and frozen in glaciers and the polar ice caps. From this small amount of fresh water, we can only use 1.0-percent. Scientists have calculated that there are more than 326 million trillion gallons of water on the Earth!
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 more significant amount of fluids, leading 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. Marine animals may breathe air or extract oxygen 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 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 lower concentration of salt in their bodies than that existing in the water. These fish drink water to regulate their salt levels and 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 procedure is regulated by a structure present in their kidneys, known as the renal corpuscle, responsible for performing necessary filtration.
Q. Do freshwater fish drink water?
A. Like marine fish, freshwater fish also drink water 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 outside the body, whereby the scales and mucous substance that covers the organism limits access to 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.