Brine shrimps live in waters which are very salty and they can even survive in saturated brine solutions. They are able to do this because they have the ability to pump salts out of themselves and, thus, can keep their internal salt concentrations much lower than those in the water in which they live. Because they are far less salty inside than outside, water leaves them by osmosis (primer on osmotic pressure) and they must drink their salty medium to replace this osmotic water loss. Of course, this imposes a further burden on their salt-exporting system because the water they drink is very salty.
This male brine shrimp, Artemia salina, has been treated with silver nitrate and photographic developer; this treatment "silver-stains" areas of its swimming legs, the metepipodites, which are actively pumping chloride ions out of the shrimp's body. [Protocol for this silver-staining method.] The metepipodites also have very high activities of the enzyme which powers the sodium pump, Na, K-ATPase, and this enzyme activity increases in proportion to the salt concentration gradient existing across the shrimp's body wall. [Protocol for the Na, K-ATPase enzyme assay I use.] These and other data are consistent with the hypothesis that cells in the metepipodites pump chloride ions out of the shrimp against large concentration and charge gradients; sodium ions leave the shrimp against a large concentration gradient but down the net electrochemical (concentration + charge) gradient across the shrimp's body wall. In this regard brine shrimps resemble marine bony fishes, which also drink salt water and use their gills to pump salts out of their blood. However, brine shrimps are much better ion pumpers and support much larger salt and osmotic gradients across their body walls than marine teleosts can.
If you would like to read a full account of ion transport and sodium pump activity in brine shrimp, the following paper may be of interest: Holliday, C.W., D.B. Roye and R.D. Roer (1990). Salinity-induced changes in branchial Na, K-ATPase activity and transepithelial potential difference in the brine shrimp, Artemia salina. J. Exp. Biol. 151: 279-296. (abstract).
Here's a list of papers on ionic and osmotic regulation in brine shrimp cited in our paper. Learn more about doing research in my lab or see a list of my former research students and their project titles with these links. Or, if you like, take a look at a list of my publications with research students or a complete list of my publications. Click appropriately to learn more about the research interests of the other members of the Biology Department.