A - Aquarium Dictionary

Updated August 12, 2019
Author: Mike - FishLore Admin
Social Media: FishLore on Social Media

Aquarium Fish Definition and Glossary

Aerobic :
when organisms need oxygen to survive they are called aerobic.

AC :
see Activated Carbon

Acan or Acantastrea Coral :
see Acan Coral

Acropora :
see Acropora Coral

Acclimate :
Acclimation is the process of introducing fish or other animals into new conditions (tank water). This process should be slow with aquarium water testing beforehand to help determine the length of time needed for the acclimation process. More information on Fish Acclimation.

Acidic :
relates to the pH scale where a measurement of the fish tank water under 7 is considered "acidic" and over 7 as "basic or alkaline" and 7 is considered "neutral". Get a pH test kit to measure your aquarium water:
PH test
pH Test Kit on Amazon

Acrylic :
this is a plastic material used to construct fish tanks, filters and other devices used in aquaria. There are many benefits to using acrylic over other materials. It is light weight, durable, inexpensive, and it can be made to be very clear to look through making it ideal for aquarium use. It is also prone to scratching easily and great care must be taken when scraping algae off the tank walls to prevent the acrylic from scratching. You can buff out scratches but this can be a very difficult project.

Actinic Light :
actinic lighting is aquarium lighting composed of lighting in the blue wave length and it should be able to penetrate deeper into the water than other wave lengths. Often times, you'll hear about saltwater aquarium keepers using a combination of full-spectrum and actinic lighting. Actinic lighting can help set off colors in corals and it can be used to help coralline algae growth.

Activated Carbon :
sometimes abbreviated as "AC", this is a form of carbon that is used in aquariums to remove dissolved nutrients and yellowing compounds to help clean or polish the aquarium water. It is often used to remove smells in the aquarium as well. It is frequently used on water faucets to filter drinking water too. Activated carbon has a limited lifetime and must be replaced periodically. How often you need to replace your carbon depends on the tank circumstances, such as stocking levels and maintenance regimen. There are various grades of activated carbon with some being better than others when it comes to leeching compounds. Some brands may release phosphates into the water. If you have a reef tank or are experiencing algae problems while using activated carbon, try testing your brand using a phosphate test kit. You may be surprised. Also see the article on Activated Carbon.

Use caution when replacing large quantities of activated carbon in your aquarium. It's a better idea to replace half at a time to prevent light shock to corals.
Activated Carbon
Activated Carbon on Amazon

Adipose fin :
the usually very small fin between the dorsal fin (top fin) and the caudal fin (tail fin). For example, you can easily see the adipose fin on Silver Dollar Fish and other characin fish.

Air Line Tube :
An aquarium air pump is a device used to force air into aquarium tubing. The tubing is placed into the aquarium (used in conjuction with an air stone) to increase water agitation and for decorative purposes. Who among us didn't have that diver with the air bubbler at one point? See below for example:
aquarium air line tube
Air Line Tubing on Amazon

Air Pump :
An aquarium air pump is a device used to force air into aquarium tubing. The tubing is placed into the aquarium (used in conjuction with an air stone) to increase water agitation and for decorative purposes. Who among us didn't have that diver with the air bubbler at one point? See below for example:
Air Pump
Air Pumps on Amazon

Air Stone :
an air stone is used in conjuction with an air pump and tubing, the air stone is placed at the end of the tubing in the tank. These "stones" are made out of sand and sometimes lime wood and have various air diffusing capabilities. See below:
Air Stones
Air Stones on Amazon

Aeration :
aeration is usually referred to in the context of "you need to increase the aeration in your tank". This means that you need to increase the surface agitation by using a device to agitate the surface of the tank water. You can do this by using air stones, power heads pointed at the water surface, and via return filters or other aquarium pumps.
Powerheads on Amazon

Ahermatypic :
corals that do not host symbiotic zooxanthellae are called ahermatypic corals. They are also sometimes referred to as the "non reef building" corals. Since they can't derive the benefits from zooxanthellae they usually have more advanced prey capture mechanisms to meet their energy needs.

Algae :
Algae can be both simple and complex in form with varieties growing on nearly any surface within an aquarium. There are brown diatoms, blue-green algae, green algae and red algae. Sometimes algae is desirous (coralline algae in saltwater aquariums) but most often if it grows uncontrolled can become a nuisance. Algae needs nutrients such as carbon dioxide, phosphates, nitrates and iron. Limiting these nutrients is key to controlling the rapid takeover of your aquarium. Some methods to control algae growth include limiting the amount of fish food entering the water, use live plants, keep less fish in the tank, increase the frequency of your water change routine, invest in a Reverse Osmosis water filter unit to filter out impurities from your tap water, and use a phospate removing medium.

Alder Cones :
usually found in shrimp tanks or aquariums that need soft, acidic water conditions. These look like smaller pine cones but are much smaller, usually around half an inch to one inch in size. They release tannins and acids that naturally lower the pH. More here:
alder cone
Alder Cones on Amazon

Algae Wafer :
a fish food designed for plecos and other bottom feeding algae eaters. The first and original algae wafers were made by Hikari and are called Hikari Algae Wafers.
Algae Wafers
Algae Wafers on Amazon

Algaecide :
a chemical that will kill algae but it may also kill other desirable life forms. Care must be taken if you use an algaecide. This is simply treating the symptoms of a larger problem. Find out why you have an algae problem in the first place. API Algaefix is an example of an algaecide:
API Algaefix on Amazon

Algae Turf Scrubber :
abbreviated as "ATS", is also referred to as a turf scrubber or algal scrubber. It is a filtration method usually employed in reef tanks where the aquarium water is sent into a separate tank (a sump, for example) and there the water passes of algae mats, cleaning the water in the process. These scrubbers have to be cropped periodically for nutrient export.

Alkaline :
alkaline relates to the pH scale where a measurement of the fish tank water is over 7 and is considered "basic or alkaline". Get a pH test kit to measure the pH of your aquarium:

Alkalinity :
Alkalinity you'll usually hear reef keepers discussing. Alkalinity is basically a measurement of how well the water in your aquarium can buffer against a drop in pH. An alkalinity test kit will measure the levels of elements such as carbonates, bicarbonates and some other elements. It is usually measured in units of meq/L or ppm which are essentially the same. See below:
Alkalinity Test Kit on Amazon

Almond Leaves :
are leaves used to add tannins to aquarium water. They are all natural, organic, rich in tannins and have (supposedly) antibacterial and anti-fungal properties. See:
Almond Leaves on Amazon

Amano Shrimp :
a freshwater shrimp that gets to about 2 inches known for their algae eating capabilities. Takashi Amano, the famous aquascaper, helped increase the popularity of these shrimp.
Amano Shrimp
Amano Shrimp on Amazon

Ammonia :
abbreviated as NH3 (one part nitrogen and 3 parts hydrogen), ammonia is released into the aquarium from uneaten fish foods, fish wastes and other biological processes. It is easily measured using an aquarium test kit on Amazon and is the first reading you'll get at the beginning of the aquarium nitrogen cycle. Ammonia is always being released into the aquarium and adequate biological filtration is needed to prevent the life forms from suffering because it is very toxic to fish. Ammonia is thought to be the number one killer of fish in aquariums, most likely due to aquariums going through the nitrogen cycle. Also, if you are doing a fishless cycle be sure to check out our fishless cycle ammonia calculator to help determine how many mL or drops to kick start your fishless cycle.
Ammonia Test
Ammonia Test Kit on Amazon

Pure ammonia that can be used for doing fishless cycles in new aquariums.
Pure Ammonia on Amazon

Amphipod :
a tiny crustacean that are a food source for many aquarium fish and invertebrates. They can range in size from 2 - 50 mm. Saltwater aquarium keepers sometimes utilize a refugium to culture amphipods.

Amquel :
this is a chemical used to detoxify tap water of chlorine, chloramine and other harmful metals. You use amquel with new tank water to prevent harming the aquarium inhabitants from these elements.
Amquel on Amazon

Amyloodinium :
the saltwater version of the parasitic single cell organism in velvet disease.

Anal fin :
the anal fin is on the lower part of the fish, in between the anal opening and the caudal fin (tail fin).

Anaerobic :
means there is no oxygen present or an organism does not require oxygen. Some of the bacteria living on the inside of Live Rock that convert nitrates to harmless nitrogen gas are though to be anaerobic. Sometimes anaerobic conditions can form in the aquarium substrate and if these areas are disturbed, harmful compounds such as hydrogen sulfide can get released into the tank.

Angelfish :
refers to either the Freshwater Angelfish or the Dwarf Saltwater Angelfish or Large Saltwater Angelfish.

Anoxic :
refers to low oxygen levels in the tank water, such as in the deeper levels of the aquarium substrate where anoxic conditions may be present.

Anubias Nana :
an easy to grow aquarium plant with low to medium light levels and a somewhat slow growth rate. More below:
Anubias Nana
Anubias Nana on Amazon

Aquarium Pharmaceuticals Inc - Most often used to describe the API Master Test kit. These test kits are used to test your water parameters and come in freshwater, saltwater and reef tank varieties with different test combinations in each. Getting a "master test kit" is often the most affordable way to procure test kits.
Apple Snail :
also known as Mystery Snail, this is a plant tank friendly snail that grows to about 2 inches in size. More below:
Also see: Apple Snails on Amazon

Aquatic Arts :
a fairly popular online seller of aquarium plants and livestock that sells through Amazon. They sell the ever popoular marimo moss balls:
Aquatic Art's page on Amazon

AquaClear :
aquarium product manufacturer primarily know for their hang on the back of the tank type power filters which are rather popular among hobbyists.
AquaClear on Amazon

Aquariology :
is the study of fish health and the management of fish health in aquariums.

Aqueon :
aquarium product manufacturer that makes economical and popular heaters and power filters. See Aqueon QuiteFlow Filter for more info:
Aqueon QuietFlow on Amazon

Aragonite :
a form of calcium carbonate, this term refers to a substrate used in the aquarium to raise or maintain high pH and alkalinity levels. Freshwater fish keepers might use this substrate to raise the pH in African Cichlid tanks and saltwater aquarium keepers use it to help maintain the pH and alkalinity levels. See below:
Aragonite on Amazon

Aquarium :
A container usually made out of glass or plastic (see acrylic) that is used to hold and view fish, plants and corals.

Aquascaping :
is the process of decorating or arranging your aquarium. This is an artistic term for situating the tank to the needs of both the aquarium inhabitants and the fish keeper and is quite fun. Also see Rock Scaping and the Aquarium Aquascaping Ideas article.

Artemia :
see brine shrimp.

Assassin Snail :
a snail that preys on other snails. Hobbyists use them to help remove pest snails from their aquariums.
More here: Assassin Snails on Amazon

see Algae Turf Scrubber.

Aufwuchs :
A German term for the tiny crustaceans, insect larvae and other organisms found living in algae and other surfaces.