Family: A scientific order of taxonomy (classification of organisms). A family is made up of related Genera.

Filter feeder: An animal that feeds off tiny food suspended in the water.

Filter medium/media: Any substance used to help with filtration.

Fish: Extremely addictive life form known to cause rampant outbreaks of aquaria in the home and rapid depletion of disposable income.

Fishless Cycle: The process of establishing colonies of nitrifying bacteria using chemical ammonia rather than live fish. The best thing to happen in fishkeeping since glass tanks. For a more detailed explanation on fishless cycling please read this article.

Flake: Flaked fish food, a staple of most fishkeepers.

Flocculant: A chemical compound used in water clarifiers. It causes fine particles to stick together to be more easily removed by the filter.

FO: Fish only.

Foam fractionation: A device used in marine tanks which sends many small bubbles through a column of water to separate dissolved organic compounds from the water. The organic compounds are skimmed off. Also called a "protein skimmer".

FOWLR: Fish only with live rock.

Fry: Baby fish.

FW: Freshwater.

General hardness: A measure of certain salts and minerals dissolved in the water - primarily calcium and magnesium.

Genus: A scientific order of taxonomy ranking below a family and above a species.

Gill cover: A hard bony plate covering the gills.

Gill: These are the respiratory organs of fish.

Gonopodium: Particular to livebearers, the gonopodium is the pelvic fins of male fish that have been converted into genital organs.

GPH: Gallons per hour.

Gravel Vacuum: A flexible plastic tube with a larger hard plastic tube at the end. Used to remove water and clean the gravel during a water change.

Gravid: A pregnant female livebearer or female who is ready to lay eggs.

Head and lateral line erosion: Also known as hole-in-head. A fish will develop pits or holes in its' head and sometimes along the lateral line. Treated with antibiotics. Can be caused by poor nutrition, flagellates or other causes.

Heater: A crucial piece of equipment for tropical fish, used to warm the aquarium water. Available as submersible, hanging, in-filter, inline and under gravel coils.

Herbivore: Fish eating mainly vegetable matter.

Hermaphrodite: An organism having both male and female reproductive organs. Many snails fall into this category.

HITH: Hole In The Head. A disease.

HO lighting: High Output fluorescent lighting.

HOB: Hang On the Back filter (aka power filter).

Hydrogen Sulphide: A toxic compound, which has an unforgettable rotten egg odour. Produced in anaerobic pockets in the substrate.

Hydrometer: Used to determine the specific gravity of a fluid. In fishkeeping, used to measure salinity.

I.D.: "Inside diameter", used when measuring tubing dimensions.

Ichthyophthirius: "Ich" A very common parasitic disease in freshwater fish. Symptoms show as white salt-like parasites on the fish, lethargy, and flashing. For More information on ICH please read this article.

Impeller: Part of a filter or powerhead looking a little like the propeller on a boat motor, and used to for the same purpose - to move water.

Internal filter: A filter which is located inside the aquarium. Examples are under gravel filters and sponge filters.

Invertebrates: These are animals without backbones. Examples of invertebrates include snails, crayfish, shrimp corals and crabs.

Iodine: A trace element especially needed by crustaceans to successfully molt and soft corals for growth.