C) Identify one species of anadromous fish and one species of catadromous fish a
ID: 257913 • Letter: C
Question
C) Identify one species of anadromous fish and one species of catadromous fish and state if they are euryhaline or stenohaline. (Note that while a bull shark can move from saline to fresh water, it is neither anadromous nor catadromous!). Clearly contrast how such fish must acclimatize to maintain osmotic homeostasis when they are in a river (freshwater) compared to when they are in the ocean (salt water). Do this by clearly summarizing how the two key problems are dealt with in a river versus in the ocean. Include definitions and relevant roles for: glomerulus, Bowman's capsule, renal (kidney) tubules, osmosis, and active transport.Explanation / Answer
Anadromous fish that include species such as Salmon are born in fresh water, and then migrates to salt waters and returns to freshwater to spawn.
Catadromous fish are found in saltwater and live their lives in freshwater and return to salt water to spawn. e.g Eels
These are mentioned fish (salmon, eels etc) are euryhaline i.e. they can tolerate a wide range of salinity from freah water to saltwater.
Osmoregulation is the active regulation of osmotic pressure so that a balance is maintained between the water and concentration of salts. In freshwater, the concentration of salt is more inside the fish than the surrounding water. Hence water enters inside the fish via osmosis to maintain a balance. The kidneys of the fish help regulate the water intake buy producing copious amounts of urine which when excreted also results in the expulsion of salts from the body. This is one of the key problems occurring in fishes in the freshwater river. This is rectified by the chloride cells that are present in the gills which take up the ions (sodium, potassium and chloride ions) from the water and transport them directly into the bloodstream of the fish. The other key problem is that the fish are hypertonic to their surrounds which means the fish has lower water concentration than its surroundings.
In ocean fish the fish have lower concentration of salts as compared to its surrounding. The chloride cells maintain the balance of ions. Also the kidneys secrete diluted urine in such waters so that minimum quantity of salts are excreted.
The glomerulus and renal tubules comprise the nephron which is the functional unit of the kidney. The production of glomerular filtrate is the first step in urine formation. The permeable capillaries of glomerulus ooze out water, salts, small proteins etc. This filtrate is collected in the Bowman's capsule which is the structure that surrounds the glomerulus. The filtrate then enters the renal tubules that is selective in nature thereby either adding or removing solutes and water turning it into urine.
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