The amount that water can be reused is governed by the limiting factors, the first of which is usually oxygen. Re-use Reverse Osmosis Method if obtaining freshwater from saltwater. The process uses a semi-permeable membrane through which pure water and not the salts will pass. The saltwater must be pressurised to approximately 25 bar, which makes it operationally expensive to produce large quantities of fresh water by this method. Spring Roccal A quaternary ammonium compound used for the treatment of bacterial gill disease .
Many roes have a commercial value, the highest being for caviar, the roe of the sturgeon.
Other commercially produced roes are those from salmon, trout, lumpfish and sea urchins. Rope See table for specifications of different fibre types. See also cable , chain Rotifers Microscopic ciliated animals. Commonly used in the culture of marine species where live diets are essential during early stages. The most commonly used species of rotifer is Brachionus plicatilis.