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Glossary of Terms

by Shari Sanford last modified Sep 02, 2007 10:16 PM
Understanding the language of Loaches Online. Here at Loaches Online we use a few special terms which have become accepted "Loach parlance" within this specialized part of the fishkeeping hobby. Below, we present these terms along with many other definitions applicable to the aquatic hobby and the study of fish.




The careful and gradual process of introducing fish into a new environment without sudden changes in water chemistry and temperature.

AcidityThe measurement of the number of hydrogen ions in water, expressed in terms of pH with below pH7 being acidic.

Activated carbonA type of chemical filter media with an incredibly high surface area, which is used to absorb pollutants from the water. Available in pre-packed bags or loose granules for packaging by the fishkeeper, it is placed into the filter where the flow of water passes through it. Ideally it will be replaced every 3 months.

AerationInjection of air bubbles into aquarium via pump or venturi action. Causes some direct dissolving of air bubbles to water, but more importantly creates water surface movement to increase gaseous exchange potential.


Affinis. Meaning 'related to, but not identical to'.


Air pumpMechanical device to pump air into an aquarium. May be diaphragm or piston driven by an electrical system. Features a valving system to force air toward the aquarium.

AlgaePlant like organisms that grow in water or on wet surfaces, they also provide a food source for grazing fish and shrimp.


The measurement of the number of hydrogen ions in water, expressed in terms of pH with above pH7 being alkaline.

AmmoniaAmmonia can be found in the aquarium in two forms, these are free ammonia (NH3) and ammonium (NH4), free ammonia is more toxic than ammonium and the ratio of free ammonia to ammonium depends upon the pH, temperature and salinity of the water. Ammonia is most toxic in warm alkaline water, the warmer the water and the higher the pH the more toxic free ammonia there is compared to the less toxic ammonium.

AnaerobicA lack of oxygen. Typical anaerobic zones in the aquarium would be oxygen-deprived areas, such as underneath a deep sand substrate that doesn't benefit from being stirred up - either manually or via the natural behaviour of burrowing fish/snail species. Anaerobic bacteria colonise these areas and convert nitrate into nitrogen gas. Hydrogen sulphide (has a rotten egg odour) and other toxic substances are also produced.

Anal fin

 The single fin on the underside of a fish between the anus and tail fin.


Anterior"In front of" a given point, e.g "anterior of the dorsal fin".

AntibioticA substance, such as penicillin, that is capable of destroying or weakening certain microorganisms, especially bacteria or fungi, that cause infections or infectious diseases. Antibiotics are usually produced by or synthesized from other microorganisms, such as molds. They inhibit pathogens by interfering with essential intracellular processes, including the synthesis of bacterial proteins. Antibiotics do not kill viruses and are not effective in treating viral infections.

AquascapingDesigning the interior of an aquarium using substrates, plants, wood, rocks or other decor.

ArtemiaGenus containing 12 species of aquatic crustaceans commonly known as Brine Shrimp. Not closely related to true shrimp. Brine shrimp eggs are metabolically inactive and can remain in total stasis for several years while in dry oxygen-free conditions, even at temperatures below freezing. The nutritional properties of newly hatched brine shrimp make them particularly suitable to be sold as aquarium food as they are high in lipids and unsaturated fatty acids (but low in calcium). The nauplii, or larvae, of brine shrimp are less than 500 micrometers when they first hatch making them an excellent first live food for many types of fish fry. Adult Artemia are also sold under the name of Sea Monkeys, or Fairy Shrimp. For further information see

BacteriaExtremely small—usually 0.3 to 2.0 micrometers in diameter—and relatively simple microorganisms possessing the  prokaryotic type of cell construction. Bacteria may be harmful or beneficial in nature depending on type.

BarbelsSensory whisker-like appendages near the mouth or chin, which aid the fish in finding food and exploring its environment.

BenthicOf, relating to, or happening on the bottom under a body of water.

BifurcatedDivided into two.


A coating on the surfaces of the aquarium which is composed of biological organisms such algae, bacteria, and protozoa.


BioloadThe amount of 'biological load' placed upon the aquarium environment, created through the metabolism process. These collective waste products produced by all the fish, have to be processed by the filtration system in order to keep the aquarium environment safe and habitable.

Biological filtrationThe action of Nitrosomonas bacteria converting harmful Ammonia into less harmful Nitrite. Nitrobacter bacteria then convert Nitrite to Nitrate. This can be further utilized by algae and plants.

BiotopeAn aquarium set up to as closely as possible replicate a piece of nature. It should replicate water conditions in the natural environment and only feature species of fish, invertebrate or plants that would naturally cohabit.

Black beard algaeActually a form of Red Algae and also called Brush Algae, Black Beard Algae thrives in high phosphate conditions. Very few fish will eat BBA although Siamese Algae Eaters (Crossocheilus siamensis) can keep it under control.


Water that has a dark tea-like colour, which is caused by humic acids. It has a very low pH, is very soft, usually devoid of excess nutrients, and is common in tropical rainforests.


BloodwormA type of freshwater gnat larave that is used as a fish food. Bloodworms are of a bright red colour due to the high haemoglobin content of their blood. They are available live, freeze-dried, or frozen, and are a good conditioning food and a firm favourite with many loach species. Bloodworm will often get picky feeders to start feeding, but as it is of a particularly rich composition, it should be fed sparingly and as part of a mixed diet. Live bloodworm is notorious for introducing disease into the tank - gamma iradiated frozen varieties are a much safer option.

Blue Moon Light
 Any type of light source that is deep blue in color. Designed to simulate moonlight and useful for viewing loaches nocturnal type activity.
BogwoodPieces of trees or roots that have been preserved by organic acids in peat bogs, and are used for decor in the home aquarium. Loaches in particular very much enjoy the shelter of bogwood, and many species benefit from the fact that bogwood helps to acidify the water and releases tannins which stain the water a tea-colour. The tannins are harmless and often accentuate the colours of softwater species, but if they are not desired, they can be removed by placing activated carbon in the filter.

BrackishWater that is neither fresh or saltwater, but is somewhere in between. In nature this occurs in estuaries, where the river meets the sea.


A small fast-flowing stream.

Buffering capacityThe degree to which aquarium water can resist changes in pH when either an acid or alkali is added.

Carbonate hardnessThe amount of magnesium and calcium hydrogen carbonates dissolved in water.

Carbon dioxide (CO2) 

 One atom of Carbon combined with two of Oxygen. Carbon Dioxide is a by-product of respiration and in an aquarium plants use the CO2 as part of their photosynthetic process.




Species of fish that eats only meat.

Caudal fin

The tail fin.


Caudal peduncleThe narrow wrist like area between the back of the dorsal and anal fins and the base of the caudal fin.


Confer.  Meaning 'compare with'. Used with scientific names to indicate a similarity to the named species without certain identification.


Chemical filtrationThe use of substances like Activated Carbon, Ion Exchange Resins and other substances to lock up, remove or modify harmful elements within the aquarium water.


An external piece of equipment that is used to cool the temperature of the aquarium water. Particularly useful during the summer months for those living in warmer climates who wish to keep temperate or coldwater species at a steady temperature throughout the year, and have no access to an air conditioning unit. A huge array of different sizes and models are available for different sized tanks. It may seem an expensive outlay, but will soon pay for itself in keeping cooler water species at life-sustaining temperatures.


Chlorine & ChloramineOne or both of these are added to tap water to make it safe for humans to drink. Although beneficial for us, it is harmful to aquatic life, and so tap water used for water changes must firstly be treated with a quality dechlorinator - usually based on sodium thiosulphate - to remove any chlorine and chloramine. Low levels of these disinfectants will cause stress and irritation to the fish's gills, with higher levels being fatal. If your water supply does contain Chloramine as well as Chlorine, do check that the dechlorinator you purchase removes both, as traditional products may only remove chlorine, leaving dangerous free ammonia in the water.



Chronic Wasting Syndrome 

More commonly known as ‘fish tuberculosis’ or ‘TB’ and is usually caused by Mycobacterium, very hard to treat because by the time symptoms are visible internal organs may well be to badly damaged.


ClickingTerm used to describe the noise productions by most Botiine loaches.

ColdwaterSomething of a misnomer, basically means an unheated aquarium.

CommunityAn aquarium set up with mixed species of fish.

ConspecificA member of the same Species.


Active during dawn and dusk.




Most often unicellular bacteria that are aquatic and photosynthetic, i.e. they can manufacture their own food. The oldest known fossil records are Cyanobacteria.




Tiny crustaceans that are a very nutritious food for small fish and are available live or frozen. It must be noted that only frozen cyclops should be used for feeding fry, as live cyclops are known to attack and kill them.


DaphniaWater-fleas, which are used for feeding small fish. Very nutritious and available live, frozen and freeze-dried.

DetritusFish waste that accumulates on/in the substrate of the aquarium. Any which is missed by the filtration system should be manually removed on a regular basis. This will help to prevent unneccessary bacterial infections of the delicate sensory barbel area, and will help keep nitrate levels in check. Can be removed by a hose siphon (for sand) and an aquarium-vacuum (for gravel). Tanks with a high flow rate rarely suffer from this problem, as detritus is stirred up into the water column and is easily removed by the filtration.

Dither fishActive, normally shoaling species of fish that are used as an indicator of the presence of potential danger or carnivores by loaches. Generally, these are small species, but larger species may be used if their is a danger of predation by larger fish in the aquarium. Active dither fish will make loaches bolder in behaviour.

Diurnal Active during the day.



Dorsal fin

The main fin located on top of the fish. 


The upper (dorsal) surface of the head or body
DropsyNot a disease in itself but a term given to the internal swelling suffered by a fish which is caused by another illness like a bacterial infection, tuberculosis, viral infection etc.


Restricted to a particular location.
EpibenthicReferring to organisms living on the bottom surface


Capable of being raised or erected, often referring to spines


The mercy killing of a creature to spare it from incurable pain and suffering. Best carried out with the use of Clove Oil.


External filtrationWater filtration system not contained within the actual aquarium itself.

FencesRaised plates on the first few rays of the pectoral fins of males of some species of Sucker-bodied Hillstream Loach. They may appear like a row of louvres.

FinrotIn probably 99% of cases the cause is either stress or poor water conditions, Fin rot is a bacterial disease involving opportunistic bacteria such as Aeromonas, Pseudomonas or Flexibacter that abound in all aquatic environments. Secondary fungal infections are not uncommon.

Fishless cyclingConsidered to be the most effective way to mature a new aquarium, can take up to 4 or 5 weeks before conditions are right for fish to be added. An ammonia based food source is used to provide nutrients for bacteria rather than using fish waste. Water conditions are monitored using ammonia, nitrite and natrate test kits, once the ammonia and nitrite levels have risen and fallen to zero and further additions of ammonia have no effect on the water the tank is then safe for fish.

FlashingSporadic striking of the body against a hard object by a fish. This is normally as a result of some discomfort or itch on the body that the fish needs to scratch. May be disease related.
Living in rivers


The length and width or "floor area" of the aquarium. The footprint is an important consideration when choosing an aquarium to house loach species. Height, of course, is also important for larger specimens, but the footprint should always be the first consideration. This ensures that these bottom-dwelling fishes are provided with as much floor area to roam as possible.


Fractional SpawnerFish that spawn by releasing a few eggs every day rather than laying all eggs at the same time.

Freshwaterwater with less than 0.5 parts/thousand dissolved salts, freshwater makes up less than 3% of the water on earth.

Frozen foodAny food source stored in frozen form. Many types of natural fish foodstuffs are available in frozen sheet or individual small block form to provide fish with natural foods without the dangers of introducing water-borne diseases. All frozen foods should be thawed before feeding to fish.

FryTerm used to describe the stage of fish development between hatching or birth and juvenile.

Fungusfungal disease of fish and fish eggs is most commonly caused by Saprolegnia, the disease will attack an existing injury on the fish and can spread to healthy tissue. Poor water conditions and over stocking/feeding are most common causes, Columnaris bacteria and/or external parasites are also common with Saprolegniasis.


***please see entries for Imperial gallon and US gallon***


General hardnessGeneral hardness, also referred to as total or permanent hardness is a measure of the total concentration of calcium, magnesium and other ions in the water. It is measured in degrees (dH), with one degree equal to approximately 17.9mg/l. The harder the water, the higher the dH.

GenusA group of closely related species

Gill Filaments

A series of projections along the posterior edge of the gill arch, the site of gas exchange.
GillsAn organ that is used for respiration, oxygen is extracted from the water and carried by the blood around the body and at the same time carbon dioxide is excreted into the water from the gills, the majority of the ammonia produced by fish comes from the gills.

GravidTerm used to describe a female fish that is either carrying fry or eggs.

Graying outTerm used to describe loss of coloration or modification of normal patterning during fighting between loaches. Generally the contrast between normally dark and light areas diminishes.


To feed on living, growing greenfoods such as plants and algae. 



Green water

Microscopic algae suspended in the water column, giving an overall green or 'pea soup' appearance to the aquarium water.



Grrrr Tank

A term coined on Loaches Online in reference to an aquarium specifically set up for a community of the more aggressive loach species.


HabitatThe ecological character of a geographical location where a fish or plant lives.


Species of fish that eats only plants, vegetation and algae.


Refers to fish of different species.


Hierarchy The determination of a fish's standing or status within a group. Botiine loaches particularly have complex social structures with an "Alpha" or lead loach heading the group.

HITH-Hole in the Head diseaseAnother disease strongly linked to poor water quality or diet, the protozoan parasite Hexamita is often present in low levels but infection usually only comes about when environmental issues allow it.

HOB filterShort for hang on the back filter. Favoured in North America due to simplicity and ease of maintenance. Generally of a box design. Water is sucked into the box by impeller action, flows through filter media and returns to the main aquarium via a weir cascade.

HolotypeThe single specimen upon which the description and naming of a new species or subspecies is based.
Transparent or translucent
HydraA freshwater coelenterate (an organism of the phylum Coelenterata, having a body wall composed of two layers of cells) that is related to the stinging marine sea anemones. The small stalk-like body may possess up to 10 slender tentacles which are lined with stinging cells and are used to capture and kill prey, which include small crustaceans, other invertebrates, zooplankton, and even small fry.

Hypo-melanisticHaving a reduced amount of melanin in the coloring. Melanin is the black part of natural coloring.

Ich/whitespotIchthyophthirius multifiliis is a ciliated protozoan which causes "Ich" or "white spot disease." This disease is a major problem to aquarists and commercial fish producers world wide. Ichthyophthirius is an important disease of tropical fish, goldfish, and food fish. The disease is highly contagious and spreads rapidly from one fish to another.
Term used to describe fish eggs and larvae.
IUCNThe World Conservation Union. Produces the "Red List of Threatened Species" through its Species Survival Commission (SSC). 

Imperial gallon

One imperial gallon is equivalent to approx 1.2 US gallons or 4.54 litres.



Indian Almond Leaves

The dried leaves of the Indian Almond Tree (Terminalia catappa). Used by many aquarists keeping blackwater species and difficult to spawn softwater fish. The leaves can be placed into a mesh bag in the filter, where they will break down and release anti-bacterial substances into the water. The water will turn tea-coloured due to the humic acid/tannins released and will have the effect of lowering the pH of the water. These leaves will need replacing every few weeks as they break down.


InfusoriaMinute organisms that are mainly used for the feeding of fry.


Species of fish that eats only insects.

Internal filtrationA means of filtering the aquarium water that is wholly contained within the confines of the actual tank.

InvertebratesLife forms lacking a back-bone.

Jaw locking 

A fight behaviour whereby two fish try to assert dominance over one another. As the name clearly suggests, the two fish concerned grasp each other by the jaws as a trial of strength.


JuvenileTerm used to describe the stage of fish development between fry and adult or maturity.

KrillVarious species of planktonic crustaceans but is mostly the shrimp Euphausia superba. This is the main food of whales, and some penguins and other seabirds; occurs in shoals in the Antarctic. Available in frozen form for feeding aquarium fish.

Lateral lineA series of pores which run along the flanks of a fish, the lateral line detects changes in pressure as well as detecting movement and vibrations within the fishes environment.

Leaf surfingTerm coined to describe the action of Hillstream Loaches feeding on aquarium plant leaves that are waving in a strong current. The leave bobs up and down with the fish on it giving the appearance of a surfer on his board.



Leucism is a condition characterized by reduced pigmentation in animals. Unlike Albinism, the eyes are normally colored.




Internet slang which stands for Local Fish Shop.




One litre is equivalent to approx 0.22 imperial gallons and 0.26 US gallons.


Loachy danceTerm coined to describe the characteristic swimming mode of many loach species most often seen after introduction to a new aquarium. Fish may swim in a vertically oriented repetative pattern singly or as a group. May also be seen in established aquaria before feeding time or as a reaction to some environmental change.

ManifoldA multi-tubed device designed to move water from one place to another. Normally associated with "River-Tank Manifold".
Refering to the upper jaw.
MaturationAnother term used for the Cycling of an aquarium.

Mechanical filtrationThe action of removing solid particles of matter from suspension in aquarium water.


A collection of measurements on a fish like standard length, total length and scale counts etc, which are used to differentiate between populations and races of fish.

MetabolisismThe chemical process occuring within a cell or organism that are necessary for the maintenance of life. Some substances are broken down to provide energy for vital processes while other life necessary substances are synthesized. Metabolism of fish and other organisms in the aquarium will be higher at elevated temperatures.

MorphometricsThe physical features of a fish like colouration and finnage etc,

Mosquito larvaeAquatic larvae of mosquito species. Often called "wrigglers". They normally hang at the water surface breathing through a tail-end snorkel. May be fed to fish as live food, but more normally available in frozen form.


A protective covering of slime (usually containing bactericides and fungicides) on the fish's skin which protects it from infection.

MulmA build-up of organic debris.

Mysis shrimpA small marine crustacean commonly frozen and used as a nutritious fish food.


The dissection of a dead fish, usually to determine why it died. 


NematodeThe most numerous multicellular animals on earth, most are parasitic but some nematodes feed on bacteria, fungi, and other nematodes.

New tank syndromeThe most common cause of New Tank Syndrome is the addition of too many fish too soon into an uncycled or not properly matured tank.

NitrateN03 - is the least toxic of the nitrgeous pollutants, it is produced by nitrobacter when they break down nitrite.

NitriteN02 - is toxic, technically it is less toxic than ammonia but nitrite problems are more common. Nitrite is produced by nitrosomonas bacteria when they break down ammonia in the filter.

Nitrogen cycleThe process in which harmful nitrogenous compounds within the aquarium are converted by aerobic bacteria into less harmful substances. Ammonia is converted to nitrite, and nitrite is further reduced to nitrate.

NocturnalActive during the night.


An 'eye-spot' marking, which resembles the eye of the fish, and if present, is usually located at the opposite end of the body to the true eyes. 




A species that eats both meat and vegetable matter.




Bony plate that protects the gills.

OrganicAnimal or vegetable matter derived from a living organism.

OsmoregulationThe process by which fish maintain equilibrium of body salts relative to their environment.

OxygenO2 - Two molecules of the element Oxygen.
Oxygen is a non-metallic element which constitutes 21% of the atmosphere by volume that occurs as a diatomic gas, O2, and many compounds such as water. It combines with most elements and is essential for plant and animal respiration.


O3 - Three molecules of the element Oxygen.

Ozone is an unstable form of oxygen which has oxidising properties and a characteristic odour. It can be used as a disinfectant or to increase the redox potential of the water, so as to optimise oxygen saturation.

ParasiteAn organism that feeds, grows and is sheltered on/in a different organism while contributing nothing to the survival of its host.


A special form of dried moss which can be used as a filter media to help soften the water and lower the pH.



Pectoral fins 

The pair of fins located directly behind the gills.



Pelvic fins

The pair of fins located directly under the gills. Also known as the ventral fins.


pHA logarithmic scale which indicates levels of acidity and alkalinity in water.

Pharyngeal teethOne to three rows of teeth found on the lower pharyngeal bone, they vary from long and pointed to small and round, also known as throat teeth.

PhosphatePhosphate is a nutrient that, whilst beneficial for plants at the correct ratios, can encourage horrendous algal blooms within the aquarium environment if left to build up to excessive levels. Many aquariums experience elevated phosphate levels, which can originate from tapwater, certain fish foods, and fish waste itself. Phosphate levels can be measured via special test kits, and diluted by using phosphate- removing media (such as Rowaphos) in the filter, or by the use of Reverse Osmosis water for water changes.


The length of time that the aquarium lights are on for.


PhotosynthesisThis is the process by which plants use the energy of light to convert carbon dioxide and water into glucose and the by-product released is oxygen.


Species of fish that eats only other fish.

Pop eyeAnother condition that isn’t a disease in itself but a condition caused by other problems such as poor water quality, bacterial infection or localised trauma.

 Positive rheotaxis
 Action of river-living fish swimming upstream towards the source of a food smell.
Posterior"Behind" a given point, e.g "posterior of the dorsal fin".

PowerheadWater pump originally designed to replace air-operated uplifts on undergravel filters. May be used in other applications where water movement is desired.

ppmParts per each million parts of (usually)water in the aquarium.



Processus dentiformis 

A term used to describe the tooth-like projection of the upper jaw, which may fit into a notch in the lower jaw - seen in Balitoridae.


Term refering to the mouth/jaw which means it is capable of extending forward.
QuarantineIsolation of new fish or other life-forms from the main aquarium in order to determine healthiness before introduction to existing stock. Quarantine may also be used to remove a sick fish from the main aquarium for treatment and thereby reduce the possibilty of further fish being infected.

RainwaterWater that falls from the clouds and is sometimes collected for use in aquariums. Rainwater is usually soft and slightly acidic, and is sometimes preferable to other sources of water which may be unsuitable for aquatic use. However, as rainwater often contains atmospheric pollutants, it should not be used for aquariums unless it is pre-filtered. It should also be supplemented with re-mineralising additives, essential for aquatic life.

Redox potentialReduction-oxidation potential. This is essentially a measure of the ability of the water to allow biological reactions to take place and is used as an indication of water quality. Redox can be measured with special electronic probes, and the higher the reading the better.

RemineraliseA term used to describe the process of boosting or adding the mineral levels of RO or deionised water.

RespirationThe biological action of the exchange of used air for fresh. This may be via lungs in land animals or by gills or other means in fish.

ReticulatedA pattern on the flanks of the fish which has the appearance of a net/netting.

Reverse osmosis (RO) waterWater that has been forced through a special membrane under pressure. It is a slow process, but produces virtually pure water. This will require remineralising with essential trace elements before use in the aquarium, but it will be free of nitrates, phosphates and other nasties. RO water should be available at any reputable aquatics store, or if larger volumes are required (e.g. for larger aquaria or multiple tanks), then units are available to install at home.

 Rheophilic Living in rivers.
RifflesAreas in rivers or streams where water speeds up while negotiating multiple small rocks and boulders. This creates much mixing of air and water and high oxygen levels.

River tankAn aquarium set up to reproduce a one-way current as far as possible in order to re-create the action of a fast-flowing river or stream. Usually associated with Hillstream Loaches.


A projecting snout or beak.




A stunted fish, or a specimen with less growth than is normally expected for the species.


SaddleMarking across the back of a fish like a saddle.

Sand SifterFish that takes in sand or fine gravel through the mouth and sifts it in the throat to remove minute food particles. Sifted material is ejected via the gill openings.

ScalelessLacking scales. Some fish lack scales and have a covering of skin. Many loaches are referred to as "scaleless" , but in actual fact have extremely small scales.

ScalesSmall plate-like dermal or epidermal structures that characteristically form the external covering of most fishes.

Scientific name

This is an internationally recognised way of identifying fish (and other living organisms). The first word indicates the genus, the second the species. The genus is always capitalised, the species lower case. Also referred to as the Latin name.


Sexual dimorphismPhysical chacteristics that show clear differences between sexes of the same species.


A behaviour noted in many Botiine species, particularly clown loaches. One or more of the smaller, subordinate fish swim as closely as possible to a larger more dominant fish, often appearing as if they are ‘joined up’ side-by-side at the gills. This phenomenon is also referred to as ‘parallel swimming’ and can become quite fast and furious with the larger fish swimming this way and that, trying to ‘lose’ the hangers-on. However speedily the dominant fish swims, and however quickly it is able to make a sudden change in direction, the smaller fish seem glued to the bigger one. This type of shadowing behaviour has also been observed as a precursor to spawning in Pangio species.

ShoalingGrouping together of multiple examples of the same fish species in a cohesive moving unit. In some species the co-ordination of movement may be helped by chemical signals released into the water by the fish.

Silicon sealant

A rubbery adhesive used for bonding aquarium glass. Ensure that an aquarium-grade silicon sealant is used for any repairs, as products from DIY stores usually contain fungicides which are lethal to aquatic life.


SiphonAction of moving liquid from a higher container to a lower level. Usually via flexible tubing, but may be via any cross-sectional shape. A suction is created to start the flow, with the exit for the water being lower than the surface of the source.

SpawningThe laying of eggs by female fish accompanied by simultaneous or immediately following fertilization by a male or males.

Standard length (SL)The length of a fish as measured from the tip of the snout to the base of the tail (caudal peduncle).

Stocking densityThe amount of biological load within the aquarium that is determined by various methods.

StressStress is caused when a fish is housed in conditions which are outside its normal tolerance levels such as incorrect or poor water conditions, incorrect diet and overcrowding.


To artificially remove eggs or sperm from fish for the purpose of breeding.




An easily avoided condition whereby fish which have been kept in cramped conditions for too long take on a compressed appearance. With Botiine species, such as clown loaches, the forehead will appear a strange steeply curved shape and the eyes look too big for the body. This not only looks unsightly, but is deterimental to the health of the fish. The external parts of the fish may slow down in growth, but the internal organs do not, placing excessive pressure on them and shortening the fish's lifespan.




Similar in appearance to the adult fish, but not yet capable of breeding. 




Occuring below the skin.


Sublacrymal GrooveA deep fold found anteriorly between the lacrymal bone and rostral cap, visible from lateral side in the Gastromyzon ridens group but absent in most other species.

Suborbital spineOften extendable spine normally hidden in a groove underneath the eye that is a defining characteristic of all species of Cobitidae. Spine may be present, but hidden beneath skin in some species.

SubstrateThe "flooring" substance of the aquarium. May be gravel, sand or a mixture of aggregate sizes.

SumpWater container sited under the main aquarium that forms part of a closed loop water-management system. The sump is fed water from the aquarium by some kind of overflow and a sump-mounted water pump returns it to the aquarium. The sump may contain several types of filtration device and also house the water heating. This reduces visual clutter within the aquarium.

Swim bladderAn internal organ that enables a fish to control its buoyancy.


A former scientific name by which a species was known that is no longer valid.

T5T5 is the term for a fluorescent light tube of narrow-diameter and which run from a different ballast unit to the standard 1" fluorescent tubes (known as T8's). The manufacturers claim that T5 lights are much more effective than a standard T8 fluorescent bulb of similar wattage. The upside is that you can squeeze more bulbs in under the hood of the tank, but the downside is that they generate a lot of heat.

TaxonomyTaxonomy is the area of the biological sciences devoted to the identification, naming, and classification of living things according to apparent common characteristics.


 Total dissolved solids within aquarium water. Most often measured by measuring electrical conductivity of the water.


TemperateA term used to describe the water temperature requirements of a fish that is neither a fully coldwater species or fully tropical species.

TerritoryThe area of habitat which an animal chooses to defend as its own.

Test kitKit consisting of marked vials for containing water samples and chemical reagents that enable determination of various chemical parameter levels by color matching to a key.


A loose description of a typical behaviour seen between fighting suckerbelly hillstream loaches, likened to that of a stingray 'smothering' the dorsal surface of another stingray, and asserting dominance.


Total length (TL)The length of a fish as measured from the tip of the snout to the tip of the tail.

ToxinA poisonous substance.

Trace elementThese are substances that are dissolved in water and which are required by fish, plants and other organisms for normal functioning. Reverse Osmosis water lacks these trace elements and it is essential that these are replaced with a mineral additive (remineraliser) before the water is used in the aquarium.

Trickle filterA container holding a media having a large surface area for colonization by nitrifying bacteria. Water trickles through the media by gravity and allows bacteria access to large amounts of oxygen to increase efficiency of the nitrification process.

TropicalTraditionally, this has been used to describe species that are best kept at temperatures in the mid 70's F (mid-20'sC) or higher.

TuberclesA round nodule or outgrowth which can be a distinguishing sexual characteristic and also an indicator of sexual maturity or spawning activity, more commonly seen in members of the Cyprinid family.


A freshwater worm that is collected for fish food, but is generally considered as quite unsafe to feed because of their preference for living in highly polluted waters. Better alternatives exist, but if they must be fed, choose the gamma-iradiated frozen form.


TurbidTurbidity is a measure of water clarity. Turbid water will contain suspended particles (of silt and other debris) and appears 'muddy'.


The rate of water flow through a filter. For loaches, the higher the total turnover rate, the better.


UlcerOpen sores on the surface of the body usually pink in colour and often with a white border of dead skin tissue. Most ulcers are superficial but severe ulcers can extend down through muscle layers even as far as internal organs. Usually a sign of disease or illness.

Undergravel filtrationA perforated plate that is fitted under the aquarium substrate. Water is pulled down through the substrate, through the plate and up a return tube using air power or a power-head pump. Bacteria colonize the substrate and help with the Nitrogen Cycle.

US gallon 

One US gallon is equivalent to approx 0.83 imperial gallons or 3.79 litres.


UV sterilizerDevice designed pass water in close proximity to a light source in the Utra-violet spectrum. Normally fitted in the return line to the aquarium after the primary filtration system. UV kills pathogens and free algae organisms.


A disease caused by a protozoan called Oödinium pilularis that infects the fins and body of the fish. The disease is not that uncommon but can easily be treated once diagnosed. Often referred to as Rust or Gold Dust disease.

Ventral fins

The pair of fins located directly under the gills. Also known as the pelvic fins.


VenturiA reduction in the internal cross-section of a tube. This causes a speeding up of water flowing through the restriction, plus a pressure drop. This causes suction and may be used to introduce air to the water stream at the narrowest part of the restriction.

War PaintDescribes the heightened color of Hillstream Loach males displaying in courtship behavior toward females or during fighting with other males. The upper area of the body darkens and the sides go paler than normal. Males will raise their colorful dorsals as a display......(Pseudogastromyzon cheni).

Water changeThe process of removing water from a tank/aquarium and adding fresh water in order to help maintain good water quality or trigger spawning activity. Adding fresh water dilutes undesirable dissolved solids. Replacement water which contains chlorine, chloramine, or other undesirable chemicals should be dechlorinated prior to being added to the tank.

Water qualityThe various factors that may be measured to determine if the overall status of the aquarium water falls within acceptable parameters for the species being kept.

Weberian apparatusThe Weberian apparatus is said to connect the hearing organ with the swim bladder, where it operates as a sounding board, thus amplifying sounds.

WeirAn edge or ramp that water flows over to a lower level. May be plain as in the return of a HOB filter, or slatted to create a crude strainer as in an overflow weir feeding a sump filtration system. In this case, the height of the weir defines the water level in the display aquarium.

Wet/dry filterFilter that allows nitrifying bacteria access to water and air. This may be as a trickle filter or by some design that cycles media alternately submerged or emersed.



A term used to describe when loaches investigate other fish with their sensory barbels. This is usually more out of inquisitiveness than any sort of aggression.

Whitespot/ichIchthyophthirius multifiliis is a ciliated protozoan which causes "Ich" or "white spot disease." This disease is a major problem to aquarists and commercial fish producers world wide. Ichthyophthirius is an important disease of tropical fish, goldfish, and food fish. The disease is highly contagious and spreads rapidly from one fish to another.


Yellow pigmentation which gives an overall gold appearance.


ZeoliteA special ion exchange material which can be used to remove ammonia from freshwater.


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