Brackish-water aquarium

The range of "saltiness" varies greatly, from near freshwater to near marine and is often referred to as specific gravity (SG) or salinity.

Generally, aquarists need to maintain a specific gravity of around 1.005 to 1.010 depending on the species being kept, but practically all brackish water fish tolerate variations in salinity well, and some aquarists maintain that regularly fluctuating the salinity in the aquarium actually keeps the fish healthy and free of parasites.

Certain kinds of brackish water fish need to have their salinity increased slightly every six months.

The tank sizes can vary widely depending on the needs of the particular species, and the temperature is usually in the tropical range of 76-82 °F.

Some freshwater species (and the blacktip shark, a marine species) are hardy enough or survive better in brackish water, such as Polypterus bichir, certain loaches, Danio rerio, all kinds of mollies but especially the Yucatán molly, and some gobies.