Question

Compare the osmoregulatory challenges faced by saltwater and freshwater fish, and the ways in which their bodies achieve homeostasis with regard to osmoregulation.

Answer 1

Question : Compare the osmoregulatory challenges faced by saltwater and freshwater fish, and the ways in which their bodies achieve homeostasis with regard to osmo-regulation?

Major problem faced by the fishes living in marine environment(salt water) is the lack of fresh water. At the same time freshwater fishes have reduced ion contents in their living condition.

Osmosis helps the organism to cope with different environment. As compared to the living environment, the fresh water fishes are hyper-osmotic in nature. So water will enter in to their body by osmosis through gill capillaries. To neutralize this effect, the fresh water fishes will continuously eliminate water through dilute urine. They eliminate dilute, very little salt containing urine. In the kidney most of the ions are reabsorbed. The freshwater fishes does not drink any water. The water is entering in to the body mainly through gills by osmosis and through food. They actively absorb the ions from the water (because fishes are hyper osmotic with their environment).

Fresh water osmolarity is 0-50 mOsm/L and by doing above describing process, the fresh water fishes maintain their osmolarity around 300 mOsm/L.

When we take the case of marine fishes, they are hypo-osmotic with their environment. So water will loose from their body through gills. To compensate this lose, they drink more water (high salt content). The salt is eliminated through gills and kidneys. Due to the high salt concentration, they eliminate concentrated urine. This will reduce the loss of water from the body.

Osmolarity of sea water is 1,000 mOsm/L. Through osmotic regulation the marine water fishes maintain their osmolarity around 300 mOsm/L.