UGF: Under Gravel Filter/Filtration.

Ultraviolet sterilizer: A unit designed to kill parasites and bacteria with ultraviolet light.

Under gravel filter: A perforated plate placed on the bottom of the aquarium under the gravel. Water is pulled through the gravel, under the plate, and up through lift tubes. Provides superior biological filtration.

UV: Ultraviolet light.

Ventral fins: Paired fins on the lower part of the fish, located below the gill covers. Not all fish have these.

Ventral Surface: The bottom area of the fish.

Venturi: A tube with a tapering constriction in the middle that causes an increase in the velocity of flow of a fluid or air and a corresponding decrease in fluid pressure. Used in powerheads and filters.

VHO: Very High Output fluorescent lighting.

W/D: Wet/Dry filter.

Water parameters: Measurements used to determine water quality. pH, ammonia, nitrate and temperature are the most used indicators.

Wave maker: A controller which switches powerheads on and off at timed or random intervals, to simulate wave action in an aquarium.

Weber's apparatus: Described in 1820 by E. H. Weber, the Weber's apparatus connects the hearing organ with the swim bladder where it operates as a sounding board thus amplifying sounds.

Wet/dry filter: A form of filtration in which the media is exposed to the air to aid in nitrification.

White worms: A small worm used as food available either live or freeze-dried.

WPG: Watts per gallon

Xenophobia: The abnormal fear of aliens.

Xenophilia: The abnormal love of aliens.

Yolk sac: A small container still connected to the fry after hatching, consisting of the unabsorbed egg yolk.

Zeolite: A naturally occurring ore, which will absorb ammonia in fresh water.

Zooplankton: Tiny animals or larvae of other animals living in water. Usually used in reference to marine aquaria.

Zooxanthellae: Symbiotic single celled brown or yellow algae living in some marine invertebrates.