Explain how marine fishes maintain the water content of their body at the normal level
Osmoregulation Definition
Osmoregulation is a process that regulates the osmotic pressure of fluids and electrolytic balance in organisms. In animals, this process is brought about by osmoreceptors, which can detect changes in osmotic pressure. Humans and most other warm-blooded organisms have osmoreceptors in the hypothalamus. Besides the brain, osmoregulators are also found in the kidneys. Types of OsmoregulationThere are two major types of osmoregulation:
Osmoconformers are organisms that try to match the osmolarity of their body with their surroundings. In other words, these organisms maintain the same osmotic pressure inside the body as outside water. They conform either through active or passive means. Most marine invertebrates such as starfish, jellyfish and lobsters are osmoconformers.
Osmoregulators are organisms that actively regulate their osmotic pressure, independent of the surrounding environment. Many vertebrates, including humans, are osmoregulatory. Most freshwater fish are considered to be osmoregulatory too. Also Read: Homeostasis Osmoregulation in Different OrganismsDifferent organisms exhibit different types of osmoregulation. Following are some osmoregulation processes in different organisms: Osmoregulation in FishFreshwater fish and marine fish osmoregulate in different ways. The environments which they have varying levels of salinity, hence the process of osmoregulation is different.
Freshwater fishes are hypertonic to their surrounding environment, which means that the concentration of salt is higher in their blood than their surrounding water. They absorb a controlled amount of water through the mouth and the gill membranes. Due to this intake of water, they produce large quantities of urine through which a lot of salt is lost. The salt is replaced with the help of mitochondria-rich cells in the gills. These cells absorb salt into the blood from the surrounding water.
Compared to freshwater fish, marine fish face the opposite problem. They have a higher concentration of water in their blood than their surrounding environment. Consequently, it results in the tendency to lose water and absorb the salt. To get around this problem, marine fish drink large quantities of water and restrict urination. Another additional energy expenditure also arises as these organisms actively need to expel salt from the body (through the gills). Osmoregulation in BacteriaBacteria use a transport mechanism to absorb electrolytes when osmolarity around it increases. The osmotic stress activates certain genes in bacteria that synthesize osmoprotectants. Osmoregulation in PlantsPlants use stomata on the lower side of their leaves to regulate water loss. Plants growing in hydrated soils compensate water loss by transpiration by absorbing more water from the soil. The plants that grow in semi-arid areas store water in the vacuoles and have thick and fleshy cuticles to prevent water loss. Osmoregulation in AnimalsAnimals have a well-developed excretory system that helps to maintain the water lost from the body, thereby maintaining osmotic pressure. Osmoregulation in HumansThe kidney is the main organ responsible for osmoregulation in humans. Water, amino acids and glucose are reabsorbed by the kidneys. When the water level in the body is high, it releases a large amount of hypotonic urine. When the water level is low, it retains water and produces a low amount of hypertonic urine. Thus, the kidneys maintain the electrolytic balance of the body. Osmoregulation in humans Aldosterone, angiotensin II, and antidiuretic hormones control the absorption process. Some water and electrolytes are also lost by perspiration. Osmoreceptors in the hypothalamus of the brain control the thirst and secretion of ADH. ADH opens the water channels of aquaporins allowing the water to flow. Thus, the kidneys keep absorbing water until the pituitary gland stops releasing ADH. Also Read:
To learn more about what is osmoregulation, osmoregulation in different organisms, or other related concepts, register at BYJU’S or download BYJU’s app. Learn more in detail about osmoregulation, types of osmoregulation, process of osmoregulation in different organisms and other related topics at BYJU’S Biology. How do marine fishes maintain their salt and water balance?As a result, most saltwater fish constantly lose water through their gills and skin. Because the fish is losing water, it must drink a lot to stay hydrated-but salty seawater is the only water around. To get rid of excess salt, the fish's kidneys pump lots of salt into its urine.
How do marine fishes are able to maintain lower internal salt concentration than sea water?Chloride cells in the gills of marine fish produce an enzyme, called gill Na+/K+ ATPase, that enables them to rid their plasma of excess salt, which builds up when they drink seawater. They use the enzyme to pump sodium out of their gills at the cost of energy.
How marine fishes maintain their hypotonic internal conditions?In such hypotonic environments, these fish do not drink much water. Instead, they pass a lot of very dilute urine, and they achieve electrolyte balance by active transport of salts through the gills.
How do freshwater fishes maintain water balance?In freshwater fishes, water will diffuse into the body of the fish, so it excretes a very hypotonic or dilute urine to expel all the excess water. Gills absorb salt to compensate for salt lost in urine. This is how they maintain water balance.
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