The Free Online Aquaculture Dictionary



The process of removal of the eye in crustaceans. This is done to promote moulting and/or spawning. The eye stalk is a source of GIH (Gonadotropin Inhibiting Hormone) and so it's removal, reduces or eliminates the signals which are stopping gonadotropins (which start and control the maturation process) from being produced


See Acrylonitril Butadiene Styrene

Supply of quality ABS pipe and fittings


A localised area of dead tissue debris and white blood cells, surrounded by inflamed (and often infected) tissue.


100%. See also nominal

Absolute pressure

Pressure measured on a gauge where zero on the gauge is equal to zero pressure i.e. a complete vacuum


The process where gasses, fluids and other chemicals are taken in by the mucous membranes, blood vessels and skin. Also refers to the transfer of nutrients across the cell membrane with required nutrients entering the cell and waste matter being discharged.


Superorder of fish including orders such as Beryciformes, Zeiformes, Syngnathiformes, Gasterosteiformes, Scorpaeniformes, Perciformes, Pleuronectiformes and Tetraodontiformes. Largest of all superorders. Dorsal, pelvic and pectoral fins usually have spiny rays, protractile mouth.


Suborder of fish (part of the order Perciformes) including fish such as Surgeonfish (Acanthurua), Rabbitfish (Siganus)


The process by which fish become used to a given environment. For example fish which are usually held at one temperature, will take time to adjust to being held at a different temperature. During the acclimation period, fish may be more susceptible to pathogens and may exhibit poor appetites and food conversion rates. Acclimation may be required for changes in water quality, lighting regimes, husbandry practices etc. Bacteria used in biological filters also require acclimation to changes in water quality, during which period they may perform their function at a reduced rate.


A compound that contains hydrogen and reacts with a base. pH<7.0

Acid Sulphate soils

Acid sulphate soils commonly occur in brackish water marsh lands, swamps and mangrove areas. The soils will often contain iron pyrite and when exposed to air or well oxygenated water, sulphuric acid is formed which can reduce the pond muds and water to pH of below 4.0 and make it unsuitable for fish culture. It can take many years of repeated filling and draining of acid sulphate soil ponds to remove the acidity from the soil. Options are to try to manage the soil with lime addition and bottom harrowing or by trying to maintain the pond full with water at all times. The oxidation of the soils is much slower in water than in air due to the smaller amounts of oxygen available. Many such ponds are now lined, as the management of such soils is very labour intensive and costly. The establishment of grass cover on the banks of the ponds  can also reduce the oxidation rate of the soils and reduce the acidification of the pond through run off. Other suggestions are that in areas of acid sulphate soils, ponds should not be dug, but dams, banks and levees built above the ground level using top soils from the inlet and outlet channel construction. the disadvantage of this is that the ponds must be filled by pumping and are at increased risk from leakage and erosion of the banks.


This refers to the amount of buffering that water requires to bring the pH to 7.0, neutral.


Order of fish (of infraclass Chondrostei) which includes fish such as Sturgeon (Acipenser) and Paddlefish (Polydon)

Acrylonitril Butadiene Styrene - ABS

Type of plastic. Abbreviated as ABS. Often used for pressure pipes. Usually solvent welded. Can be directly solvent welded to U-PVC. High impact strength. High abrasion resistance. Non toxic. Taint Free. Operating temperature range -40oC to +80 oC. Not resistant to organic acids, ozone. Partially resistant to chlorinated water.

Distributors of ABS Pipe and Fittings

Activated Carbon

Available in granules (GAC) or powder. Granules are usually more practical for commercial use. Removes negative ions from the water (such as ozone, chlorine, fluorides etc.) Once used it can be recharged by heating to 900oC. Not generally financially viable for commercial systems. Sometimes used in small hatcheries, especially where mains water is being used and chlorine and other chemicals added to the water must be removed.

Activated Sludge

Process where nutrients are kept suspended in the water by pumping or more commonly aeration. A mixture of free floating bacteria and algae utilise and convert the nutrients through processes such as nitrification and photosynthesis. Fish are reared in the ponds, usually at stocking densities of below 15 kg/m3. The fish in such systems will often taste muddy and must be kept in clean water for a period of up to one week prior to harvest. Such systems are used in some countries for fish such as tilapia. They enable higher stocking densities than normal, static green water systems (ponds). The systems are limited to areas where there is sufficient year round light and temperature for the bacteria and algae to perform. The systems are more difficult to control and predict than more conventional water treatment systems such as recirculation units, and due to the high B.O.D. in the water, the energy required to add oxygen to the water is often higher than the pumping costs which would be associated with recirculating the water to a separate treatment system where a lot of the B.O.D. could be removed from the system.


A rapidly developing disease or process. Used to describe a disease outbreak where the stock are rapidly affected, often dying without showing many symptoms. The term acute is not used to describe how severe a condition is, only the speed at which it is developing. See also Chronic

Acute catarrhal enteritis

Another name for Infectious Pancreatic Necrosis (IPN)

Acute toxicity

Causing death within 96 hours pr less after a brief exposure period.

Ad libitum

To the limit. In respect of feeding this term is used to describe when the fish are fed freely until they reach satiation point

Adipose tissue

Body tissue which is able to store high amounts of neutral fats. For example the adipose fin found in Salmonids and some other species.


A compound added to a vaccine to increase the immune response.

Adrenal Glands

Glands responsible for production of some hormones. The inner section of the adrenal gland produces adrenaline and non-adrenaline. The outer part of gland secretes small amount of sex hormones (androgens and oestrogens) as well as corticosteroids. Located about the kidney.


Formation of a thin film on a surface


The process where air and water are mixed. This may be in the form of bubbling air into water, or letting water fall through the air. The process is usually used to increase the oxygen concentrations in water. The efficiency of aeration equipment is determined by the amount of surface area interface between the water and air and the energy required to produce that interface. A summary of the devices used and their corresponding efficiencies is shown in the table. It is also used for other processes such as degassing, mixing and destratification.


The name given to a process which requires oxygen. For example aerobic bacteria, require oxygen to live. The opposite of aerobic is anaerobic.

Aeromonas salmonicida

Gram negative bacteria that is the causative agent of the disease Furunculosis.


The cause of a situation or problem.



A device which causes turbulence such as a paddlewheel or other device with rotating blades / parts.


Combination of gasses making up the earth's atmosphere Typically 78% nitrogen , 21% oxygen, 0.9% argon, 0.03% carbon dioxide with the remainder being a mixture of trace gasses plus water vapour.

Air Cooling

This process uses towers or columns, packed with media to break up the water as it falls. The water forms a thin film on the media as it runs across it. If air is blown through the tower, it will cool the water as it passes across it. Cooling is achieved in two ways - Evaporative cooling, where heat is lost into the air as the water evaporates (the same way that if you put a solvent on your hand it feels cool as it evaporates), and conductive cooling where, if the air is cooler than the water, heat will pass directly into it. Trickle Biological Filters can also be used as cooling towers if air is blown through them. Air cooling can be very efficient, depending on the relative water and air temperatures.

Air Curtain

see Bubble Curtain

Air Dryers

Air dryers use either a heat source or a chemical (such as the silicon pouches, that are found in packaging for items like shoes to protect the products from rotting) to remove the moisture from air. They are mainly used to dry air before it enters machinery such as an ozone generator. Air dryers usually either use refrigeration techniques or chemicals which absorb the moisture and require replacing. For large application, refrigeration is usually the choice because of the cost and  management time of the chemical replacement option..

Air - Friction loss

See Friction Loss - Air

Air Lift

see Airlift

Air Lock

Air locks are pockets of air that form in pipes, if there is nowhere for the air to escape to. Bubbles often get drawn into pipes as a result of vortexes at inlet points, or if the pipe entrance is not fully submerged. Bubbles can also form in pipes as a result of gas supersaturation. If the pipe travels in an upward slope at some stage, and then slopes down again, there is a risk that the air will collect a the highest point in the pipe. This can then restrict or even stop the flow of water through the pipe. The solution is to either ensure that pipes always slope downwards, an air vent, or air purger at the point where the air collects in the pipe.

Air Purger

A device used to expel air from piped water systems. Typically the device has an internal float. As the air builds up inside it, the float falls, opening a valve at the top. The water pressure in the pipe pushes the air out. As the device fills back up with water again, the float rises and the valve shuts.

Air stripping

The removal of dissolved gasses from water by a mechanical means which involves the movement of air across water. The stripping of carbon dioxide is relatively easily achieved, stripping of supersaturated gasses is easy down to a saturation level of 103-105%, after this it becomes increasingly difficult, and requires increasing amounts of energy to remove the gas. Vacuum systems can help achieve 100% or below. Stripping of ammonia from water is only cost effective at pH levels of higher than 10.0 and therefore not relevant to fish farming. A small amount of ammonia can be stripped by air at lower pH levels, but the amount is usually insignificant when the total ammonia production is taken account of. See also degassing



A contained column of bubbles and water used to pump, provide flow or current. The air lift uses a bubble source (usually a diffuser) to supply bubbles to the bottom of a column (often a pipe or similar). As the bubbles mix with the water, they create a mix which is less dense than water alone. Because of this, gravity has less effect on the water and it rises higher than the water around the column, which has no air in it, and is therefore denser. An opening at the top of the column allows the water/air mixture to escape. The head and amount of water that an air lift can pump is a function of the ratio of air to water, the amount of air pumped in, the depth of the diffuser, the ratio of the submerged part of the column to the part of the column that protrudes form the water and the diameter of the pipe. Air lifts cease to work so well once the bubble to water ration becomes so high that the bubbles begin to join together and form much larger slugs of air. Airlifts are also sometimes used on cage farms, taking the water and any feed / faeces in it, from the bottom of the cage to the top, so that the farmer can see if his stock are eating all their feed. They have also been used in cages as fish pumps.


The life stage of a fish when the yolk sac is still present. Also called sac fry.



Algae are simple celled plants and (like all plants) contain chlorophyll. This traps energy from the sun and uses that energy to convert nutrients and carbon dioxide (which are dissolved in the water) into growth. When grown in a hatchery, the growing and multiplying algal cells are collectively known as a culture. The main form of algae that is of interest to aquaculture is collectively known as unicellular. These consist of free floating cells of algae which make the water look green or brown, depending on the colour of the algae. There are many different types of unicellular algae but only a few are nutritionally suited for good growth. These are divided into two types; flagellates, which can swim by the action of one or more flagellae and diatoms, which have an outer shell made of silica. Some of the more commonly grown species and their sizes are listed in the table. Other forms include filamentous, which are strand like colonies of algae, which usually form dense mats or clumps, and blue-green algae, more commonly referred to as cyanobacteria. As well as being grown for food for the fish and also as food for zooplankton, which are then fed to the fish, algae impacts on aquaculture in other ways. These include algal blooms, taints, oxygen depletion, supersaturation and fouling

Algae control

Algae can be controlled by either chemical (see herbicides), mechanical or biological methods. The mechanical methods generally involve light elimination (by floating black polythene or black bubble wrap). Filamentous algae can be removed by netting or dragging out. Care should be taken when using light elimination as the dying algae can result in high oxygen demands and lead to fish kills. Biological methods involve the used of species such as silver carp (Hypothalmichthys molitrix) which eat the algae.

Algal bloom


An algal bloom occurs when light, temperature, water currents and water quality (especially the amount and type of nutrients in the water) combine to form perfect growing conditions for a species of algae. The algae multiply very fast and depending on their colour, the water turns green, blue, red or brown. Algal cell counts in the water generally exceed 5 million per litre. The algae can cause damage to the fish by suffocation as it takes all the available oxygen out of the water for the purpose of photosynthesis or by causing the gills to become clogged with algae and function poorly. Certain species of algae (e.g. the blue green algae's) can produce a toxin which is poisonous to fish and can cause mortalities. Algal blooms are particularly common in areas where there is a nutrient build up in areas of poor water exchange, such as beneath cages or in static ponds where fertiliser and/or artificial diets are used. The only method to ensure that algal blooms do not occur is to remove the nutrient source. Once all the available nutrients have been used up, the algae mass reaches a critical point where it can no longer sustain itself and dies off (often very quickly). In static ponds, the algae cell mass is retained in the pond and is broken down, releasing the stored nutrients. This cycling of nutrients leads to a recurrence of the bloom (although sometimes with different algae species) at a later date. Blooms typically occur in the Spring, when the rising water temperatures, increased daylength and light intensity enable algae to multiply and make use of any available nutrients that have built up in the water during the Autumn and Winter (either as a result of breakdown of previous algae blooms or new nutrients entering the system). After the Spring, when all the nutrients are used up, the algal mass dies off and is broken down into it's constituent nutrients and made available again. This often causes a second bloom in the late summer / early Autumn. The term "red tide" is often used to describe blooms of certain species of algae which contain red or orange pigments.  these pigments can give the bloom a vivid red / orange colour, especially when the bloom dies off and the green chlorophyll that masks the pigment is reduced and the colour of the pigment shows through.

Algal Scum

A floating mass of filamentous and/or unicellular algae which can restrict the penetration of light to the water column. It can be removed either physically, by mechanical filtration or by biological filtration which will remove the nutrients that it depends on for growth.


Derivative substance of seaweed, used sometimes as a binder in feed formulation.


A non-native species for the area


A single dosage of a drug or a chemical which is in solution.


A compound which has an excess of hydroxide ions. A substance which combines with acid and neutralises it, forming a salt. pH >7.0


Alkalinity is a measure of the concentration of bases in the water and the capacity of the water to accept acidity (I.e. it's buffering capacity). Alkalinity is usually measured as either mg/l (milligrams per litre) CaCO3 (Calcium Carbonate) or meq (milli-equivalents). 1 meq = 50 mg/l CaCO3. The ideal range of alkalinity for fish farming is 20 - 300mg/l. Below 20mg/l the water will have a very low buffering capacity, and any acids that are washed into the water (for example after heavy rain has soaked through peat), will cause a big fall in pH. Such fluctuations of pH are harmful to fish. Water with low alkalinity can be treated with lime. High alkalinity levels can sometimes lead to a condition in the fish called nephrocalcinosis.


A gene (in a diploid fish) is supplied with a single allele from each of the parent fish. For example the gene may be responsible for the expression of eye colour, with one allele giving a blue colour and the other a brown colour. One allele becomes more dominant over the other (which is termed recessive) and this denoted the expression of the gene. In the case of the eye colour, the blue allele may be dominant in which case the gene will make the eyes blue.


Altitude has a bearing on the amount of dissolved gas (such as oxygen) that water is capable of holding. At higher altitudes the water contains less oxygen than at lower altitudes. 


Aluminium is used in many farms as screens, hatching trays and also as a construction material for some items of plant such as filters etc. The material is generally long lasting, but use in very acid waters should be avoided as this can lead to the build up of aluminium in the water, which is toxic to fish. It's use in seawater systems should also be avoided as the seawater oxidises the aluminium. Where aluminium is not suitable, 304 or 316 stainless steel should be used. In some areas where there is an abundance of aluminium in the ground, and acidic waters prevail, dissolved aluminium can cause severe problems to fish. These problems most often occur where there is run-off from industry/mining activities


The normal (natural) environmental conditions.

Amino acid

The building block of proteins. The quality of a specific protein source is down to it's make up of different amino acids



The unionised form of ammonia (although sometimes used to express the total ammonia (i.e. unionised and ionised). Symbol NH3. Toxic to fish. See unionised ammonia for more details on toxicity. The amount of ammonia produced by the fish is approximately 0.03 x feed (for commercial diets). Therefore for every 1000g of feed that is fed 30g of total ammonia is produced. This is excreted by the fish in the urine and across the gills. The ammonia production will vary throughout the day with the 0.03 value being the average. In systems where the feeding regimes are confined to a few large feeds over a short period, the maximum ammonia production at any time may be twice this amount, with corresponding periods of very low ammonia output.

Ammonia stripping

see Air stripping



Ammonia-nitrogen refers to the part of ammonia that is made up of nitrogen. The chemical symbol for ammonia is NH4. This means that it consists of one Nitrogen atom (N) and four Hydrogen atoms (H). The atomic weight of Nitrogen is 7, and that of Hydrogen is 1. Therefore a molecule of ammonia has a total atomic weight of 11 (7+1+1+1+1). Nitrogen therefore comprises 63.6% of the total weight of ammonia (7 / 11 x 100%). When ammonia concentrations are referred to as ammonia-nitrogen, they are only referring to the nitrogen part of the compound, which is only 63.6% of the ammonia concentration. The term is used in aquaculture, as it is the nitrogen part of ammonia, which is used to calculate how much nitrite and nitrate will be produced, following biological filtration of the ammonia. To convert ammonia to ammonia-nitrogen, multiply by 0.636. To convert ammonia-nitrogen to ammonia, multiply by 1.57. See also ammonia



The ionised form of ammonia, symbol NH4. Non toxic to fish. See also Unionised Ammonia, Ammonia nitrogen
Can be used in some forms as a herbicide against Elodia sp. (common name Canadian Pond Weed). Applied at 225kg / ha to dry pond as a preventative measure. 

Ammonium Chloride 

NaCl. Chemical often used to start biofilters. The addition of ammonium chloride serves to provide an ammonia source so that the biofilter can begin to mature before fish are introduced. This can help prevent ammonia or nitrite toxicity in new systems.

Ammonium Nitrate

NaNO3 Chemical used in starting biofiltration system, especially where there is denitrification in the system which requires the nitrate source.


Without any fixed shape


Term used to describe the height of a wave. The measurement is taken from the crest to the mean half way point to the trough.


Suborder of fish (part of the order Perciformes) including fish such as Gourami (Osphronemus). Able to breath air through specially adapted respiratory organs


A fish which spawns in freshwater and lives most of it's life at sea e.g. Atlantic Salmon (Salmo salar)


A reduction in the number of red blood cells. Limits the ability of the blood to carry oxygen and other nutrients around the body, and excretion of waste products (such as carbon dioxide). the reduction in the red blood cells results in the starvation of tissues of oxygen and other nutrients. Anaemic fish typically show pale gills, due to the reduced number of red blood cells.


The term used to describe a biological process which occurs without the need for oxygen. Often used to describe types of bacteria and bacteriological processes such as denitrification. Anaerobic bacterial activity can be seen in the bottom muds of ponds, lakes etc., where organic matter is broken down without the availability of oxygen. The thin crust of the surface muds, prevents the oxygen from penetrating through to lower layers. Such anaerobic breakdown in muds can result in the production of hydrogen sulphide, which can be toxic to fish.


An agent (usually chemical) which can cause partial or complete loss of sensory awareness, ability to feel pain and ability to carry out muscle movements.  Not all anaesthetics achieve the full range of effects (e.g. hypnotics such as metomidate and etomidate, which do not block pain well), and a number of the common drugs which have pain-relieving (analgesic) ability may stimulate marked transient stress via their
depression of the subject's central nervous system.

Anaesthetics are sometimes used in aquaculture for the following purposes ; transportation, prior to slaughter, broodstock handling/injections etc., administration of vaccines/drugs, tagging. If anaesthetics are to be used for stripping broodstock, the fish must be rinsed and dried before stripping as any anaesthetic can affect sperm motility and egg quality. A list of the more common anaesthetics used in fish culture are given below. Before using then one should check the following: 1. If they are licensed for use in your country, 2. Test a few fish first as the speed and depth of anaesthesia varies fish size, species and water quality, 3. Special licences may be required for the use of anaesthetics, especially if they are to be injected, 4. Workers are protected from the effects. See also Sedation, Carbon dioxide

Analogue (1of 2) - Signal.

A function which can give a proportional state. Unlike a digital signal which can only instruct a device to be on or off, an analogue instruction can tell a device to be at any number of states between on and off. For example a digital signal can only turn a pump on or off., whereas an analogue signal can not only turn the pump on or off, but can also regulate the speed of the pump (e.g. 20%, 30%, 40% of full operational capacity etc). Analogue signals are increasingly being used for dosing functions using the feedback from a probe. For example an output from oxygen probe may give a tell a controller that the oxygen concentration is changing in a tank. The controller will send out an analogue signal to partially open or close the oxygen supply valve, in an effort to maintain a steady oxygen concentration at all times. This is more preferable than having just an open or closed valve (as would be the result from a digital signal), as this can give rise to peaks and troughs of oxygen which can stress the fish. Analogue outputs come in a variety of signal types, all of which give a band of operation proportional to the controller output requirements e.g. 4-20mA band will give a value anywhere between 4 and 20mA. Other common analogue outputs are 0-20mA, 0-1volt and 0-100mV.

Analogue (2 of 2)  

A copy of....for example some artificially produced hormones are analogues of the naturally occurring hormones.


Device dropped onto the sea bed to secure a floating vessel. The best type and size of anchor for a given situation depends on the sea bed type and the angle of the anchor chain / rope. See also chain, cable and rope

Anchor Ice

The term given to a specific type of ice which forms under the water. The phenomenon occurs when water temperatures are almost 00C (32oF) and air temperatures are below freezing (usually < -4oC). Bubbles of very cold air are drawn into the water through water splashing (at weirs or pipe outlets) and as the air in the bubble is below freezing, the bubbles become coated with ice. This reduces their buoyancy and causes the icy particles to travel in the water column. The ice particles "stick" to each other in the water and also "stick" to the surfaces of pipes etc. Once there is a coating of ice on a surface. Other ice particles readily stick and the coating builds up. Anchor ice can cause particular problems in long pipe runs, where the bore of the pipe is gradually reduced by the thickening ice layer, and also on screens (where maters are often worsened by the fact that many screen designs cause air to be drawn through with the water.).


A substance with a male hormone activity such as Testosterone


This process involves the irradiation of the egg before fertilisation. This means that only the male parent contributes to the genetic make up of the offspring. This process then results in the offspring being all male, a desirable attribute in some species. It also allows cryopreserved sperm to be used to fertilise eggs. In this way a library of sperm from proven broodstock could be held in storage and used in the future to create off-spring with the same characteristics as the original broodstock which may have died years ago.


Offspring produced through androgenesis

Entry submitted by Shmuel Rothbard


Order of fish (part of the superorder Elopomorpha) which includes fish such as European eel (Anguilla anguilla), Moray eel (Muraena). Absence of pelvic fins, reduced pectorals and elongated body.


A negative ion


A growth ring that is found on scales, opercula and in otoliths. Like rings on a tree. Counting of the rings can assist in determining the age of a fish and the number of times it has spawned.


Device which plays a message (e.g. as found in an alarm panel)


Oxygen deficiency in the blood cells or tissues of the body to such an extent that it causes physiological and/or psychological disturbance


Deficient in oxygen. Anoxic areas are sometimes found a few inches down in silt and muds, where organic matter has settles and has been broken down the bacteria. The upper layers of silt act as a barrier against oxygen transfer to the lower layers and so the muds become devoid of oxygen. Such situations can often occur in the bottom of heavily stocked ponds with a poor water turnover rate or beneath cages. The build up of such anoxic areas can lead to the production, and release into the water of Hydrogen Sulphide which is toxic to fish. See also Azoic zone


Towards the front (opposite of posterior)


A chemical which destroys or expels parasitic worms


Chemicals used to treat bacterial infections. There are many different antibiotics available. Most are administered with the feed, although some valuable fish may be injected. Antibiotics are usually given under the supervision of a veterinary surgeon, and care should be taken to follow the complete course through, to prevent the build up of resistance in the bacteria. If antibiotics are to be incorporated with the feed, this is most effectively done at the feed mill where more controlled mixing can be carried out. If carried out on site, a cement mixer is often used to mix the feed with the dry antibiotic, before finally adding a spray of vegetable or fish oil to bind the antibiotic to the pellet. The more common antibiotics and their dose rates are listed below. Care should be taken to ensure the following when using antibiotics 1. If they are licensed for use in your country, 2. Special licences may be required for their use or on farm mixing, 3. Special licences may be required for their injection 4. Workers are protected from contact as much as possible, 5 Proper Withdrawal periods are observed. See also Vaccines


A protein which is produced by the fish, in an effort to neutralise the effects of a foreign material (such as a pathogen) entering the body


Antifoulants are chemicals that are coated on to surfaces to prevent algae, seaweeds and marine organisms from attaching to the surface. Some chemicals that have been used in the past and some that are still used, create conflicts with environmentalists, ecologists and shellfish / crustacean farmers and fishermen. This is because the chemicals leach into the water and affect the wild stocks.


A substance which is not normally found in the body, but which, if added to the body, will produce an immune response.


A chemical which is added to feedstuffs to stop fats breaking down. Vitamin E is a commonly used anti-oxidant in fish feeds.


The prevention of infection by administration of chemical agents (biocidal or biostatic) to damaged tissue.


Herbicide used to control submerged macrophytes. Applied at 18.8 litres / ha. See Herbicide


A formation of rock that holds a reservoir of ground water



Proper name for the crustacean, the brine shrimp. Harvested from certain areas of the world (such as the Great Salt Lake in the USA). The shrimps lay cysts which are packed dry and have a long shelf life. Contact with water activates the cyst and the development and hatching process begins. The artemia are used to feed marine fish larvae and some freshwater species (such as cyprinids). The nutritional make up of the artemia can be boosted by the addition of several commercially available compounds. See also Live Feed

Artesian Well

A well where although the water table is below the ground level, geological pressures force the water up to the surface when a borehole is sunk into the water bearing rock. (which underlies an impervious rock formation.). Ground water can therefore be obtained without the need for pumping.


Fluid accumulation in the peritoneal cavity.

Ascorbic Acid

Vitamin C. Water soluble vitamin important for the construction of connective tissues. A lack of vitamin C can cause abnormalities of the spine and a reduction in the ability of the body to heal wounds. Other deficiency symptoms may be seen, depending on species


Reproduction without eggs and sperm e.g. bacteria are asexual as they multiply by dividing.


Suffocation as a result of too little oxygen or too much carbon dioxide in the blood. Can be brought on by high ambient carbon dioxide concentrations which can restrict the ability of he fish to excrete carbon dioxide.


A device for aeration and water flow creation. The device consists of a float(s), a motor, a hollow shaft and a propeller. The hollow tube is open to the air at one end and submerged at the other. The angle which the tube is mounted at is adjustable. A motor turns the propeller and creates a directed current of water. The alignment of the end of the shaft and the propeller are such that air is drawn down the shaft and mixed in with the propelled water. See aeration for comparison of efficiency with other devices.


The conversion of digested food to body tissues and fluids.


Astaxanthin is a naturally occurring chemical in the family of carotenoids. It is the principal pigment that gives salmonids their pink colour. It is produced for addition into fish feed in the latter part of the production cycle to ensure a good flesh colour. Astaxanthin has largely replaced the use of Canthaxanthin as the main pigment used in salmonid diets, due to adverse publicity about the latter. Pigment levels are typically in the region of 50 - 60 mg/kg feed. Modern feeds, with higher energy levels and low FCRs mean that the pigment level often has to be increased, especially if the fish are supplied to Japan or the French smokehouse markets which both demand a very deep colour. Much of the astaxanthin used in fish diets is extracted from a yeast (Phaffia rhodozyma) which contains over 0.1% astaxanthin as a dry weight.

Asymptomatic carrier

An animal that shows no signs or symptoms of a disease but harbours it and is capable of transmitting it to others. Such animals can be responsible for a disease, previously thought to be eradicated from a farm appearing again after a long period. E.g. A wild fish in the water course supplying the farm can become infected by the pathogen, but as it lives in a natural, stress free state it does not manifest itself as a disease. This can also be apparent in systems where different species are held, where one species is largely unaffected by the pathogen but may harbour it, the other species may be susceptible to it.


Order of fish (part of the superorder Atherinomorpha) includes fish such as Garfish (Belone) and Flying Fish (Exocoetus)


Superorder of fish including the order Atheriniformes. Generally small surface feeding fish with protractile upper jaw.

Atmospheric pressure

The pressure exerted by the weight of air above the measured point at any point on the surface of the earth.


Damage and wastage of tissue due to nutritional deficiency, disuse or nerve damage.


Not usual in a normal condition; opposite of typical


Device for lifting materials. Uses a rotating, enclosed screw which lifts the material as a result of the screwing action. Used with some success for lifting fish and water together. Not as flexible as a fish pump in that the angle of lift is restricted and means that the auger sometimes takes up too much space. One advantage is that it can gently handle very large fish (in excess of 5kg), which most other types of  fish transportation systems will not. Also used for conveying feed to and from hoppers.


An electronic device that is included into alarm panels to automatically dial a series of telephone numbers when an alarm condition exists. Some are linked into annunciators, which play a taped message.


Organisms not requiring carbon in their diet. Such organisms are able to grow on inorganic salts only.

Available oxygen

see oxygen


Denotes the absence of bacteria; opposite - Xenix

Axial Flow pumps

See low head pumps


The region immediately behind the base of the pectoral fin

Azoic Zone

The area of sea/pond bed directly beneath a cage farm. Large downward flow of nutrients (food and faeces), very little life. May vary according to currents, tides etc.