Aquarium & Tropical Fish Site

Fishkeeping Glossary
A quick reference guide for expressions commonly used by fishkeepers...

 Age of Aquariums > Aquarium Articles


Here is a listing of some frequently used words, acronyms, abbreviations, expressions and other jargon used by fishkeepers in general or on this site in particular. The definitions or explanations presented here are focused on briefness and clarity rather than completeness and accuracy, so that you may quickly familiarize yourself with the gist of the term you're looking for. In some cases further reading is suggested and, as always, you can search the site (see link under the top title bar) to find where and how else that term was used on the site.
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 Acclimatization – Gradual introduction of new fish to an aquarium by equalizing the temperature and chemical parameters of their container water with that of the tank. Minimizes Stress.

 Acidic – Water with a pH less than 7.

 Acrylic – A clear plastic material used to construct aquariums. It is half the weight of glass and its refractive index is closer to that of water than glass, making it more transparent. Acrylic is more easily scratched than glass. Also called Plexiglas.

 Actinic – A type of fluorescent bulb that gives off blue colored light often used in marine aquaria to make corals appear to glow with brilliant colors and to give the tank a "deep ocean" feel to it.

 Activated Carbon – A Filter Medium used to remove organic contaminants or residual medications from aquarium water. If used it must be renewed at regular intervals.

 Adipose Fin – A small fleshy fin located behind the dorsal fin in some fishes, e.g. certain Characins.

 Aerobic – Existing or active in the presence of free oxygen.

 Air Pump – A small electric pump, usually of the diaphragm type, used to deliver air to an aquarium.

 Air Stone – A finely perforated ceramic, glass or wooden block which diffuses air from an Air Pump into the water in the form of tiny bubbles.

 Algae – Plant-like organisms which grow in water and attach themselves to aquarium glass, plants, rocks, decorations, etc. There are many types of Algae. An overgrowth of algae is generally considered unsightly and a nuisance (but see Aufwuchs) and can create water quality problems. Always present in water, their growth is stimulated by excessive nutrients (overfeeding fish).

 Algal Bloom – An explosive growth of Algae which discolors the water and can lead to oxygen depletion.

 Alkaline – Water with a pH greater than 7.

 Alkalinity – The ability of water to maintain a stable pH. Controlled by the amount of carbonate ions present in the water. Also called Buffering Capacity. See KH.

 Ammonia – An extremely toxic byproduct of fish metabolism and the decay of organic materials. In a fully Cycled tank the ammonia is totally converted to Nitrites and eventually Nitrates by the Bio-Filter.

 Anabantid – see Labyrinth Fish.

 Anadromous – A fish that is born in fresh water then migrates to a brackish or full salt environment as it grows. Compare Catadromous.

 Anaerobic – Existing or active in the absence of free oxygen.

 Anal Fin – Fin just behind anal opening.

 Annual – See Killifish.

 Anoxic – Low oxygen.

 Aquarium Salt – Additive-free salt which is used in the treatment of certain freshwater fish diseases or conditions, or added to the freshwater aquarium in very small quantities where it may be beneficial to certain types of fish. Not to be confused with marine salt which is a complex mixture of salts used in saltwater tanks to create ‘artificial’ sea water.

 Aquascaping – The artistic arrangement of plants, rocks, and driftwood to create a harmonious and aesthetically pleasing display in an aquarium. The acknowledged master of the art is the Japanese Takashi Amano. See Dutch Tank.

 Aragonite – A form of calcium carbonate which constitutes the shells of corals and other marine creatures. Crushed Aragonite sand is sometimes used as a Substrate when it is desired to raise the pH/Hardness of the tank water above its natural level, e.g. for African Lake Cichlids.

 Artemia – See BBS.

 Astaxanthin – Carotenoid pigment supplement and antioxidant added to many foods to enhance reds, oranges, and yellows in fish. May be purchased already added to foods or separately as a powder additive.

 Aufwuchs – A German term that is used to refer to Algae growing on rocks, driftwood, etc. If not excessive it can be decorative and provides food for some types of fish and Inverts.

 BBA – Black Beard Algae, Black Brush Algae, or Red Algae. Looks like short black, dark-green, or dark-red hairs growing on plants and decorations. High phosphate content in the water encourages its growth

 BBS – Baby Brine Shrimp. Larvae of brine shrimp, crustaceans of the genus Artemia. Cultivated as food for fry and small fishes.

 BGA – Blue-green Algae or Cyanobacteria. Aquatic bacteria that make their own food through the process of photosynthesis. Can rapidly overtake an aquarium, by spreading over everything in sheets. May smother and kill plants if not removed.

 Bio-filter – Biological Filter. Any device or Substrate which provides an attachment site for the nitrifying bacterial colony in an aquarium. See Nitrogen Cycle.

 Bio-load – Biological Load. The waste output of organisms that must be processed by the bio-filter. In a balanced system, the bio-load does not exceed the ability of the Bio-filter to process all the waste. See Cycle.

 Biofilm – A slimy matrix produced and inhabited by bacteria which enables the bacteria to adhere to a surface and carry out certain biochemical processes essential to the Nitrogen Cycle. In open aquatic environments, biofilm supports a microscopic community of various species of bacteria including nitrifying bacteria, algae, protozoa, and microscopic invertebrates. In the aquarium, biofilm covers all surfaces exposed to water, and tends to build up in the dark, undisturbed areas such as the filter intake tube and other filter parts.

 Biotope – A natural region or geographical space that presents relative uniformity of physical characteristics and animal/plant populations which inhabit it.

 Biotope Aquarium – An aquarium that is designed with the intent to reproduce an existing natural habitat or niche, in terms of its physical/visual characteristics and its naturally occurring species. See Biotope. Also see Theme.

 Black Water Extract – Home-made or commercially prepared water conditioner to create the dark, very soft and acidic water typical of Amazon Basin rivers. The chemistry and dark color is due to decaying vegetation causing high humic acid levels.

 Bloat – (a.k.a. Malawi Bloat) A potentially fatal condition caused by flagellates (protozoan parasites) proliferating in the intestines. Symptoms include loss of appetite, white, trailing feces, and bloated appearance. Common in African cichlids.

 Blood Worms – Larvae from the non-biting midge family Chironomidae. Live, frozen, or freeze-dried, they are a food item that is highly appreciated by most fish. Often used to condition fish for breeding and stimulate growth.

 Bogwood – Wood that has been preserved in a peat bog.

 Brackish – Slightly salty water typical of river estuaries and lagoons. Some fish, e.g. archer-fish, gobies, and puffers require a brackish aquarium set-up to thrive.

 Buffering Capacity – The ability of water to maintain a stable pH. Controlled by the amount of carbonate ions present in the water. Also called Alkalinity. See KH.

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 CO2 – Carbon dioxide. Used in Planted Tanks to maximize plant growth.

 Canister Filter – An external Filter consisting of a sealed canister containing various Filter Media and a pump which circulates water through the media. It is attached to the aquarium by inlet and outlet hoses.

 Carbon – See Activated Carbon.

 Carnivore – A meat-eater.

 Catadromous – A fish that is born in salt water but migrates to fresh water where it grows to adulthood. Opposite of Anadromous. The common eel is one of the few examples.

 Caudal Fin – The "tail fin." In many species this is the main fin associated with propulsion.

 Characins – Loosely, a large group of fishes that includes (the mainly South American) Tetras and also some predators such as the Piranha.

 Chelate – Refers to a chemical complex where iron or some other mineral is tightly bound to an organic compound. This facilitates the uptake of iron and other trace elements by aquarium plants.

 Chloramine – Combination of Chlorine and Ammonia that is frequently added to municipal water supplies to maintain municipal water quality standards. Also prevents the establishment of Biofilm in municipal water supply lines and storage containers. It is toxic to fish and amphibians. Can be removed by treating water with a Water Conditioner that is specifically formulated to treat chloramines..

 Chlorine – Chemical element that is frequently added to municipal water supplies as a disinfectant. Prevents Biofilm establishment in municipal water supply systems. It is toxic to many fish and inverts. Less stable but a stronger disinfectant than Chloramine, it can be dissipated for aquarium use by allowing the water to stand in an open container for 24 hours, or it can be instantly removed by treating water with a standard dechlorinator.

 Cichlids – (Pronounced: SICK-lids) A huge family of Old and New World fishes whose vivid colors and interesting social behavior make them very popular with Fish-keepers.

 Clamped Fins – Posture adopted by fish where it holds its fins tightly against its body. Usually a sign of distress or sickness.

 Clutch – The deposit of eggs left by a female fish. See Spawn.

 Community Tank – An aquarium which is populated with fish of several different species, all of which are compatible with one another.

 Cory – Common abbreviation for Corydoras, a genus of small South American armored catfish with many different species that are very popular in home aquaria.

 Cycle – 1. v. To establish the nitrogen cycle in an aquatic system by promoting the establishment of nitrifying bacteria. 2. n. The Nitrogen Cycle.

 DI Water – Water that has been purified by deionization.

 DIY – Do It Yourself. Rather than purchasing an item ready-made, or having a custom item made by someone else, the DIY project involves assembling and/or constructing something from parts and materials purchased, collected, and/or fashioned by the hobbyist.

 DSB – Deep Sand Bed. A sand bed Substrate deep enough to create anoxic areas in which denitrifying bacteria can reside. Used to keep nitrate levels low in an aquarium. See Plenum.

 Daphnia – The ‘water flea,’ common crustaceans found in freshwater lakes, ponds, and slow moving streams. Cultivated or collected in the wild as fish food.

 Dead Spot – An area of poor circulation, either within the Substrate or in the Water Column.

 Denitrification – The conversion of Nitrate to nitrogen gas carried out by certain species of bacteria in Anoxic conditions.

 Diatom – Microscopic organism with a hard shell that remains after the death of the organism.

 Diatom Filter – A Filter which employs the use of diatom powder (the skeletal remains of diatoms). Used to ‘polish’ the water by filtering out particles as small as 1 micron.

 Display – To ‘show off’ by fully extending all fins and exhibiting full or special coloration, and/or special movements of the body and/or fins. Usually associated with breeding, can also be for dominance or territoriality.

 Dither fish – Fish added to an aquarium with shy or nervous fish. The dither fishes’ unconcerned behavior signals to the shy fish that it is safe to come out of hiding, and/or that it is safe to breed. Compare Target Fish.

 Diurnal – Active during the daylight hours.

 Dorsal Fin – The fin at the top of many fish. In many species of fish (such as cichlids) is distinctly separated into a spiny front portion followed by a "soft" rear portion.

 Driftwood – Wood that has been drifting or floating in water.

 Dropsy – A condition in which the body of the fish becomes swollen due to accumulated fluids. It is not a disease in itself but a symptom of various diseases which may become fatal if not treated.

 Dutch Tank – An aquarium which is designed to display plants in beautiful Aquascaped arrangements. It may or may not contain a few fish.

 Egg Layer – Species of fish where the female lays eggs which are externally fertilized by the male. The most common method of fish reproduction. Compare Livebearer.

 External Filter – Any filter that is located outside of the tank, e.g. HOB Filter, Canister Filter.

 FO – Fish Only. Saltwater aquarium containing fish but not Live Rock or Reef animals.

 FOWLR – Fish Only With Live Rock. A saltwater aquarium that contains only fish and Live Rock.

 Ferts – Fertilizers. Nutrients added to the water to improve or maintain health and growth of aquatic plants.

 Filter – A device which removes particulate and chemical impurities from, and circulates aquarium water. See article.

 Filter Media – Various materials used in a Filter which remove particles and impurities from the water by mechanical, biological, and/or chemical means.

 Fin Rot – A condition in which the fins are rotted away giving the appearance of ragged, split, or perforated fins.

 Fish-haver – One who has fish in home aquaria, without purposeful consideration for the fish's health or wellbeing.

 Fish-keeper – One who has fish in home aquaria, and tries to maintain optimum conditions for the fish.

 Fishless Cycle – To Cycle an aquatic system without live fish, using chemical or household ammonia, or decaying material such as fish food or a piece of shrimp to promote the establishment of nitrifying bacteria (as Biofilm). See article.

 Flaring – Spreading out the gills and fins as a form of Display. The Betta splendens is known for his display of flaring.

 Flashing – A quick twist-like movement made by a fish to scrape part of its body against an object in the tank, usually done to eliminate parasites or other sources of skin irritation.

 Fluorescent Lighting – A relatively cool, energy-efficient artificial light source. Produced by gas discharge (ionization) in a low-pressure tube. The recommended and most common type of lighting used for aquaria. Compare Incandescent.

 Fry – Fish larvae (baby fish).

 GH – Total Hardness (also referred to as General Hardness). A measurement of the amount of magnesium and calcium dissolved in water. Expressed in degrees of hardness. One degree of hardness equals 17.9 ppm. See also Buffering Capacity, Hard Water and Soft Water.

 GPH – Gallons Per Hour. The rate at which a filter turns over x amount of Gallons in one hour. For example, a filter that turns over 150 gph will filter 100% of the water in a 10g tank 15 times in one hour.

 Gallon – When used on this site without qualification, usually refers to the US Gallon, equal to 3.785 Liters. The UK Gallon is equal to 4.546 Liters.

 Gonopodium – Modified Anal Fin in male Livebearers, used to transfer sperm to females.

 Gram-negative/Gram-positive – Named after Danish physician Hans C.J. Gram. Bacteria stained with colored dye according to Gram’s method are designated Gram-negative when it does not hold the color, and Gram-positive when it retains the color. Some antibiotics are more effective against Gram-negative bacteria, while others are more effective against Gram-positive bacteria. Broad-spectrum antibiotics treat both Gram-negative and Gram-positive bacteria.

 Gravel Vacuum – 1. A device made of a large diameter rigid tube attached to a smaller diameter flexible hose. Used to clean gravel Substrates by siphoning water and debris from the gravel during a Water Change. 2. The process of cleaning the Substrate by means of the Gravel Vacuum.

 Gravid – The condition in which a female fish is full of eggs and ready to Spawn.

 Gravid Spot – Dark marking which can often be distinguished at the rear of the abdomen of female Livebearers (Platys in particular) indicating advanced pregnancy. What is seen are the embryos, particularly their eyes, showing through the female’s abdominal wall.

 Green Water – Water with a green appearance due to free-floating Algae.

 Grow Out Tank – A separate tank into which Fry are transferred until they grow to a size suitable for sale, or until they are large enough to be moved back into the aquarium with adults.

 HO – High Output Fluorescent lighting.

 HOB Filter – Hang On Back Filter. An External Filter which is hung on the back of the tank.

 HOT Filter – Hang On Tank Filter. An External Filter which is hung on the tank. Some are not intended for permanent installation, but only for short-term use, and are placed in front or on the side of the tank.

 Haplochromine (Haplochromis) – Any cichlid from the African Rift Lakes and certain other regions currently or formerly belonging to the Haplochromis genus (often abbreviated to Hap). An example of a haplochromine group formerly classified under Haplochromis but currently under a different classification is the genus Astatotilapia.

 Hard Water – Water which has a high concentration of dissolved minerals and solids.

 Herbivore – One that eats mainly or only vegetable foods.

 Hitech – Aquariums that make use of sophisticated equipment and acessories.

 Hospital Tank – A separate tank in which sick fish can be isolated from the main tank population while undergoing treatment. See Quarantine Tank.

 Hybrid – A cross between two or more different species.

 Hydrometer – An instrument used to measure salinity by Specific Gravity.

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 Ich – The fish parasite Ichthyophthirius. The main symptom of infection is small white spots on the body of the fish, like grains of salt. Also called White Spot disease.

 Incandescent – Artificial light source produced by an electric current passing through a wire inside a vacuum, heating the wire to high temperatures to produce light. Compare Fluorescent. Only five percent of the energy output of Incandescent lighting is light, while the remaining 95% of the energy output is heat.

 Infusoria – Microscopic or minute animal life which commonly occurs in water containing decaying organic matter. Includes paramecia, euglena, desmids, rotifers and others. Cultivated as food for Fry and small fishes.

 Instant Cycle – To Cycle an aquatic system using bacteria (Biofilm) from an existing system, or the commercial product Bio-spira.

 Internal Filter – Any filter mounted entirely inside the tank. The Sponge Filter is the simplest example.

 Inverts – Invertebrates. Animals characterized by a lack of a backbone or internal skeleton. May have an exo-skeleton or shell.

 Jump Start – To accelerate or bypass the initial cycling period of a newly setup tank by adding a filter, filter media, gravel and/or water that has been running on an established tank.

 Jumper – Said of a species or specimen that tends to jump out of the aquarium.

 K – Kelvin – Temperature scale used to designate light intensity. For freshwater 6400K-10000K is optimum. For marine 6400K – 20000K is optimum.

 KH – Carbonate Hardness. A measurement of the amount of dissolved carbonate and bi-carbonate ions in water. Expressed in degrees of hardness on the German scale (Ί dH). One degree of hardness equals 17.9 PPM. See Buffering Capacity.

 Killifish – Egg laying toothcarps. (Compare Livebearers). There are two types of Killifish, the Annuals and the non-Annuals. Annual Killifish inhabit temporary bodies of water that completely dry up during part of the year. These fish have a short lifespan and rapid growth rate, reaching maturity within a few months. They lay eggs that remain dormant until the conditions are favorable for hatching, when the rainy season returns. Their eggs are incubated by aquarists in a special way to imitate this (see Peat). Non-annuals have a longer lifespan, but most also have the ability to lay eggs that can survive a short dry season.

 LFS – Local Fish Store.

 LPS – (1) Local Pet Store. (2)Long polyped stony corals which require high intensity lighting.

 Labyrinth Fish – Fish from the family Anabantoidei. Characterized by a specialized respiratory organ, the labyrinth organ, which enables the fish to obtain oxygen from the air, allowing it to live in water with low levels of dissolved oxygen. This family of fishes includes bettas and gouramis.

 Laterite – Iron- and mineral-rich soil material, a layer of which is sometimes placed below a layer of gravel in the Substrate of Planted Tanks to provide plant nutrition.

 Light Hood – The cover of an aquarium which contains the light fixtures for illuminating the Tank.

 Lip-lock – Two fighting or courting fish grab each others’ mouths and in this position continue to wrestle one another. Lip locking during fighting can be dangerous as it can result in torn or damaged mouths.

 Live Rock – Calcium carbonate skeletons of corals or other calcareous organisms colonized by beneficial bacteria and micro and macroscopic marine life that live on and inside it.

 Livebearer – Live bearing toothcarps. Species of fish which carry their offspring internally until birth. Common livebearers are guppies, mollies, and platys.

 Loricarid – The Loricariidae, or sucker-mouth catfish, is a huge catfish family whose members include the many Plecos which are very popular with aquarists.

 Lowtech – Aquariums that do not make use of sophisticated equipment and acessories.

 MTS – 1. Malaysian Trumpet Snail (Melanoides tuberculata). A cone-shaped, freshwater snail which burrows in the Substrate and bears live young. 2. Many Tank Syndrome.

 Mantis shrimp – Common name for predatory marine crustaceans of the order Stomatopoda. These crustaceans have powerful, modified appendages which they use for defense and in subduing prey. The ‘smashers’ have calcified, club like appendages, while the ‘spearers’ have sharp, pointed appendages. Often seen as pests, they are known as ‘thumb-splitters’ and for their ability to break aquarium glass, but some species are prized for their attractive coloration.

 Marine – Refers to a saltwater aquarium or environment.

 Marine Rotifer – Brachionus species. Live food cultivated to feed marine Fry and other marine organisms. The Rotifer itself has little nutritional value, but it can serve as a food delivery system for the needed nutrients provided through the food (usually micro algae) that fills their bodies.

 Mbuna – (Pronounced um-BOO-nuh) African word for "rockfish." Rock-dwelling cichlids from Lake Malawi, Africa.

 Median Fins – Fins that are unpaired.

 Metal Halide Lights – Very brilliant and broad-spectrum lights used in some Planted Tanks for growing plant species that demand high-intensity light to thrive, and in saltwater Reef Aquariums.

 Milt – Fish semen.

 Mouthbrooder – Fish which protect their eggs and/or young by holding them in the mouth. Some may also clean their young in a similar fashion.

 Mulm – Solid waste materials such as plant parts, fish excrement and leftover food in various stages of decomposition. Aquatic 'compost' which benefits plants, but in an unplanted, poorly maintained system may result in a buildup of humic acids which will decrease pH over time leading to Old Tank Syndrome.

 NO – Normal Output Fluorescent lighting.

 Nano Reef – A small Reef Aquarium.

 Nitrate – The nitrogen compound at the third stage of the Nitrogen Cycle. Nitrate can be used by plants, further processed into nitrogen gas through Anoxic bacterial processes, or reduced by regular partial Water Changes.

 Nitrite – Intermediate nitrogen compound in the biological conversion of Ammonia to Nitrate in the Nitrogen Cycle. Nitrite is toxic to fish, but less so than Ammonia.

 Nitrogen Cycle – The natural process (nitrification) by which bacteria convert fish waste and other decaying matter into less harmful compounds. See article.

 New Tank Syndrome – Condition in which toxic fish waste products exist in the aquatic system because the Nitrogen Cycle has not yet been established.

 Nocturnal – Active at night.

 OFS – Online Fish Store.

 Old Tank Syndrome – Condition in which organic acids, excess nitrates, and other products accumulate in the aquarium, causing gradual decline in pH or a sudden pH crash. Caused by lack of proper maintenance of the aquarium including regular partial Water Changes.

 Omnivore – One that eats meaty foods and vegetable foods.

 Ovipositor – The reproductive organ through which a female fish deposits her eggs. In some fish this is always visible, as in the female Betta splendens where it appears as a small white bump at the base of the abdomen.

 PFS – Pool Filter Sand. Coarse-textured sand for use in aquariums housing digging and/or sifting fish. Heavy sand not prone to being taken up by filter intake like the lighter, fine-textured sands.

 pH – Measurement of the degree of acidity of water. pH 7 indicates neutral water. Less than 7 is Acidic, and more than 7 is Alkaline. See Water Parameters.

 PMDD – Poor Man's Dupla Drops. A do it yourself water column plant fertilizer intended to duplicate Dupla Plant 24, Daily Fertilizer.

 PPM – Parts per million.

 Paludarium – An aquarium that is set up with a dry land area as well as a water area.

 Papilla – A tube descending from the abdomen of male fish used to fertilize eggs. It is typically only visible during breeding. See Milt.

 Peat – Partially decomposed plant matter, mainly sphagnum moss. Used for storing Annual Killifish eggs in a moist state. You can also incubate non-Annuals on top of it. Also used as a Substrate layer for planted aquaria and as a Filter Medium. Softens water and reduces pH.

 Pectoral Fin – These fins are on the sides of the fish. They are often used for more precise maneuvering. In a few species they are used for propulsion.

 Pelvic Fin – Paired fins towards the underside of the fish. Vary in size and shape greatly. In anabantids often elongated. Appear to function as ‘brakes’ especially for species which move in a start/stop motion.

 Piscivore – One that eats other fish.

 Planted Tank – A freshwater aquarium in which a significant quantity of aquatic plants are growing. Plants may cover from say 30 to virtually 100 percent of the Substrate surface. The plants form an important part of the aquarium ecosystem. An aquarium with only a few plants is not considered a Planted Tank. In a Planted Tank, the fish remain the most important feature and the plants complement them. Compare Dutch Tank.

 Plec, Pleco – Common abbreviation loosely applied to many species of the Loricarid family of armored catfish and other similar fish, not just to the type species Hypostomus Plecostomus. Popular to the hobby. There is a myth that spelling out the name in full will result in the death of their fish, which is why on aquarium-related boards and sites they are sometimes referred to as pl*cos.

 Plenum – A space between the aquarium bottom and substrate, created by supporting the substrate above the bottom using UGF plates or some other support structure. Used to keep Nitrate levels low in a saltwater aquarium. Water and organic waste diffuses down into the plenum where the wastes concentrate. Nitrifying bacteria in the upper levels of the substrate use the oxygen and produce nitrate in the water as it moves down into the space. Denitrifying bacteria living in the oxygen-poor lower levels of the substrate slowly convert Nitrate into harmless nitrogen gas.

 Power Head – A small submersible electric pump. Often used in conjunction with Filter or UGJ systems.

 Protein Skimmer – Used in saltwater tanks to remove organic pollutants from the water before they break down. Also called Foam Fractionator. Produces tiny air bubbles which attract and hold pollutants, which are then deposited into a separate container.

 Quarantine Tank – A separate tank in which newly acquired fish are kept for some time to insure that they are not suffering from any disease before they are released into the main aquarium. Also used as a Hospital Tank.

 R/O Water – Water that has been purified through the process of reverse osmosis. Also referred to as RO water.

 Reactor – Dosing device which adds reagents to tank water. E.g. a CO2 reactor (of which there are many types) mixes CO2 (carbon dioxide) from a pressurized or DIY system into the tank water.

 Reef Aquarium – A saltwater aquarium featuring live corals to simulate a coral reef with a selection of Invert inhabitants. It may or may not include reef fish. Such aquariums place extremely high demands on lighting and water quality.

 Refractometer – An instrument used to measure salinity by refraction, the amount light deflects from a straight line through a medium.

 Refugium – A separate tank which shares water and filtration with the main aquarium. Used for growing Nitrate reducing Algae, raising live food, and isolating inhabitants from the main tank.

 Reverse UGF – A UGF system where the water is pumped up through the gravel bed rather than being drawn down. Theoretically.

 Rhizome – A plant organ which resembles a horizontal stem from which leaves grow. Anubias and Java Fern are common aquarium plants which grow from a rhizome. It is important that the rhizome lies on top of the substrate and is not buried within it as roots usually are, otherwise it will rot and the plant will die.

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 SPS – Small polyped stony corals which require high intensity lighting.

 Salinity – The amount of salt in the water. Measured by Specific Gravity or Refraction.

 Saltwater Bath or Dip – A therapeutic technique for helping to remove some kinds of parasites from many freshwater fish. Salt is added to conditioned water and the fish is placed in the solution for a period of time to rid it of external parasites and stimulate slime coat production.

 School – A group of one kind of fish oriented together in a synchronized fashion, with uniform distance between individual fishes, traveling at the same speed and/or oriented in the same direction and position.

 Scientific Nomenclature – A standardized system used to name fish (and all other living creatures) which assigns a unique two-part name in which the first word indicates the genus and the second the species, e.g., Corydoras paleatus, the peppered Cory catfish. This is a valuable help, even to the hobby Fish-keeper, since common fish names can vary greatly from country to country, and even within the same country.

 Seasonal Fish – See Killifish.

 Shimmy – A stress-related symptom in which a fish remains in one position while wagging it’s body from side to side. Common among Livebearers, especially Mollies, when water conditions are not within the parameters for the fish’s needs.

 Shoal – A group of fish loosely gathered together but with variable distance between individuals and moving in various directions and/or oriented in various positions. Fish that shoal together will often school when on the move or in response to a threat.

 Siphon – An arrangement whereby water is induced to flow naturally from an upper level to a lower level through a pipe or hose which spans an intermediate level that is higher than either.

 Slime Coat – The continuously produced mucous envelope which covers the scales of a fish and makes it feel ‘slippery.’ Its purpose is to act as a barrier against disease-causing organisms, to act as a buffer in the internal/external gas exchange systems of the fish, and to save energy by reducing friction with the water when swimming. When a fish is subjected to Stress the Slime Coat becomes thinner.

 Soft Water – Water with a low content of dissolved minerals and solids. Usually Acidic.

 Sparring – Aggressive encounters between two fish (usually males) involving Display, Lip-Locking, or other forms of contest.

 Spawn – 1. v. To deposit and fertilize eggs. 2. n. The fertilized eggs of fish. The offspring of fish.

 Spawning Mop – Acrylic yarn tied together to provide a place for fish to Spawn.

 Species Tank – Also Species Aquarium. One in which fish of only one species are kept. Compare with Community Tank.

 Specific Gravity – A measure of density in comparison to pure water at a specific temperature. In this context, it is used as a measure of Salinity.

 Spike – A sudden increase in the concentration of certain chemical substances in the aquarium water, such as ammonia or nitrite.

 Spirulina – A type of Blue-green Algae often fed to both saltwater and freshwater fish. Contains pigments that enhance blues and greens in fish.

 Sponge Filter – A simple Internal Filter in which water is drawn through a synthetic sponge which traps particles and provides a surface on which nitrifying bacteria can grow.

 Stress – A condition in which the organism is subjected to unfavorable or unfamiliar environmental conditions, resulting in some alteration in normal physical functioning. Short-term stress can often be overcome. Long-term stress can reduce resistance to disease and parasites, inhibit self-healing processes, and reduce life-span.

 Substrate – 1. The material spread out on the bottom of the aquarium, such as gravel, sand, or layers of different materials. Used as a planting medium or for decoration and attachment site for Biofilm. 2. Any surface on which living organisms are attached.

 Sump – A water reservoir below a tank (usually a marine aquarium) through which water is circulated by means of gravity and a pump. The sump can be used to house filters, heaters, and other equipment to keep them out of sight. In addition, it increases the total water volume of the aquarium system and thus helps to stabilize it. Some maintenance tasks can be performed in the sump, reducing the need to disturb the main tank and its inhabitants.

 Swim Bladder –An internal air sac which can contain more or less air according to the needs of the fish at the time. More air helps the fish become more buoyant, while less air allows the fish to swim down to deeper levels. Also called Air bladder. Serves to keep fish properly oriented in the water. Also creates and amplifies sounds.

 Swim bladder Disease – A condition in which the Swim Bladder fails to function normally. Causes vary. Symptoms include an inability to maintain normal upright position, or difficulty swimming down to lower levels of the water column.

 Target fish – Fish added to an aquarium with aggressive breeding fish. These fish serve as a ‘common enemy’ upon which the breeding pair can vent their aggression, preventing the pair from attacking each other. Compare Dither Fish.

 Theme – A looser equivalent of the Biotope Aquarium, it gathers fishes and/or plants coming from different biotopes but from the same general region, e.g., "Amazon Theme" or "South-Asian Theme".

 Trace Elements – Chemical elements which are required, usually in tiny quantities, for healthy growth of fish, plants, and invertebrates. These elements are normally supplied by regular water changes or in salt mixes for marine aquariums, but in certain cases it may be necessary to supplement this.

 Trickle Filter – A type of Bio-filter in which water to be purified trickles over the media held in a tray or chamber not submerged in water. This increases the amount of oxygen available to the bacteria, promoting Nitrification.

 Turnover – Or Turnover rate. The rate at which the total volume of the tank water is processed through the Filter system. Three or four times per hour is usually the minimum for a freshwater tank. Certain aquarium situations often require many times this basic turnover. See GPH.

 UGF – Under Gravel Filter. Perforated plates rest on the aquarium bottom and support the gravel substrate. Using lift tubes and power heads, water is pulled down through the gravel, up into the tube, and returned to the water column. Not usually recommended.

 UGJ – Under Gravel Jets. A DIY system of pipes and outlets set up to circulate water just above the Substrate, to reduce Dead Spots or the accumulation of Mulm on the Substrate. A pump or power head forces water through a network pipes which are buried under the gravel. Water is forced through outlets placed at various positions above the Substrate, keeping the particles in suspension until taken up by the Filter.

 VHO – Very High Output Fluorescent lighting.

 Velvet Disease – Fish disease caused by the protozoan parasite (Piscinoodinium). Also called Gold Dust. The main symptom of infection is dusty or velvety patches on the skin ranging in color from grey to a rusty yellowish-red.

 Vent – 1. n. The uro-genital opening of fish, located between the anus and the anal fin. Also referred to as the genital papilla. 2. v. To determine a fish's gender by examining the genital papillae.

 Ventral Fins – Pelvic Fins. The most posterior (toward the rear of the fish) set of paired fins on the underside of the fish.

 Venturi – A simple device for introducing a gas, e.g. air or CO2, into a water stream in a pipe.

 WPG – Watts Per Gallon. The wattage put out by the aquarium lights per gallon of water in the tank. For example, a 10 with two 15 watt normal output Fluorescent lights will give you 3 watts per gallon.

 Water Change – To remove some of the water from an aquarium and replace it with fresh water. See article.

 Water Column – The water in the aquarium from the top of the substrate to the surface of the water.

 Water Conditioner – A chemical product formulated to treat tap water to make it safe for aquarium use. Water conditioners usually eliminate Chlorine and Chloramines but may also contain ingredients that bind heavy metals, detoxify nitrogen compounds, fortify the Slime Coat of fish, and have other beneficial effects.

 Water Parameters – The readings for measurable factors of water in an aquarium. Basic aquarium water parameters include Ammonium, Nitrite, Nitrate, pH, General Hardness, and Buffering Capacity. See article.

 Wet/dry Filter – A type of Bio-filter in which water flows across a special Substrate on which Nitrifying bacteria (as Biofilm) are attached. The Substrate is not submerged, but kept moist and moving in and out of the water, by the action of the water. Promotes Nitrification by increasing the availability of oxygen to the Nitrifying bacteria.

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The initial version of this Glossary was produced as a join effort by the following members of our Message Board:

Haname, Azrien, Benedictj, DJ Mix, Huntress, The Kapenta Kid, Andrew Brown, Matt (TVI), Joseph (noname), Marcos Avila.

oF <=> oC in <=> cm G <=> L