The Free Online Aquaculture Dictionary
Tagging of organisms is used in aquaculture primarily to enable the tracing of specific animals and family groups etc. whilst rearing them as part of a larger mixed group. Many farms use tagging techniques for broodstock, enabling easier management as they can be reselected should their offspring perform well. There are many types of tag, including some which can cause a lot of physical damage to fish, such as those which penetrate deeply into the muscle. More modern tagging techniques use microchips (PIT tags), which are inserted just under the skin. The microchips can then be read with a special scanner much like a barcode. Such modern techniques are less damaging to the fish, which is especially important where the tagging is being used for trials, as the ability of some fish to cope better with the tag, will influence the result of the trials. A third type of tagging involves using a device (Panjet) to inject a measure of dye into the skin or fin of a fish. These dye markings are limiting in their lifespan (which can be up to 1 year) and are also limited in the number of variations that can be used, to identify individuals.
Flavour that can be imparted to the flesh of a fish as a result of it's
environment. Can render the fish unmarketable. Often associated in fish reared in earth ponds, where the fish can take on a muddy
flavour, which is thought to be due to certain types of algae which are ingested. Fish reared in
recirculation systems can also carry taints, the cause of which is uncertain, but is related to
compounds that can be broken down by the addition of
ozone to the water. In general, if sufficient ozone is being added to a recirculation systems to keep the water clear, taints will not be a problem.
Pollution incidents (such as diesel spillage) can also impart taints to the flesh. Taints can be flushed out of fish by holding them in a clean, taint free water supply. The time taken for taints to be removed is dependant on the type and intensity of the taint. Muddy flavours and those associated with recirculation systems, can in general be removed by a few days in such holding facilities. Taints such as diesel, can take many weeks to disappear.
Total Ammoniacal Nitrogen See Ammonia nitrogen
There are three main tank designs used in aquaculture,
Round tanks, D-ended
tanks, Raceways (although there are many variations to the basic types). Due to the cost of construction, tanks are usually only used for hatcheries and the
intensive culture of high value
species. See also screen
design, scouring velocity
Parasites that infect the gut of the fish. Of commercial importance in some cyprinid species (especially Caryophyllaeus fimbriceps and Khawia sinensis) and occasionally others (e.g. salmonids - Diphyllobothrium sp. which has been connected with outbreaks of P.K.D.). Often associated with other animals such as oligochaete worms (see also Tubifex tubifex) which ingest the eggs excreted by the adults.
Disease affecting shrimp species. Thought to be a virus which is complicated by the use of
certain pesticides / herbicides in banana plantations. Responsible in the past for the decimation of many shrimp farming areas. Some farms now
experimenting with the use of filtration (including ozone systems) to remove the pesticides / herbicides from the water before entering the farm.
Organisms which comprise of a particular taxonomic entity e.g. a particular class, family or genus. See also classification
A category used in classification.
|Tea Seed cake
A residue that remains after the oil has been
extracted from the seeds of certain plants of the Camellia family. The
residue is compressed into a cake and contains saponin which is
most aquatic life as it reacts with the blood. Used widely to eliminate
fish and insects from ponds prior to stocking. The saponin detoxifies
quickly in the water and is not toxic to cattle or humans who use the water.
Generally administered at 10-25mg/l as a piscicide.
Group term for bony fishes (i.e. those with vertebrae).
Derived from the word Teleostei, a taxon of uncertain category (e.g.
suborder, class). Falls within the Subclass Actinopterygii. Of the fish in
the group, the soft rayed fish such as salmonids, herring and carps are
considered relatively primitive, but the spiny rayed fish such as perches
are considered more progressive
Tail of the abdomen in crustaceans
A region where the weather is neither extremely hot or extremely cold. Sometimes defined as the region
between the Tropic of Capricorn and Antarctic circle in the Southern Hemisphere and
between the Tropic of Capricorn and the Arctic circle in the Northern
Measurement of heat. As fish are cold blooded their metabolism is temperature
dependent. A fishes metabolism increases with temperature. All fish have an optimum temperature for growth and
food conversion rate.
This can vary between species and sometimes between
strains of species. Fish will become increasingly
stressed at temperatures outwith their normal growth range and will cease to feed. In general
oceanic marine species are more stenothermic than freshwater and coastal fish, as they have evolved to
temperature changes of the ocean which are slower and less extreme than other environments. For species
where the limits are unknown, it is wise to look at their natural environment and the
temperatures that they regularly experience, and use these as a guideline. Sudden changes in
temperature (even as low as 2oC) can stress fish. When fish are being transferred to water of different temperature, every effort should be made to reduce
temperature shock to a minimum. Growth rates and egg development rates are
governed by temperature (see degree days). Optimum temperatures for some species are given below, however these should be regarded as
guidelines only, as they can change with different developmental stages and acclimation: See also
|Tertiary amyl alcohol
Anaesthetic used at a rate of 1 - 10 ml/l in water.
Hormone secreted by the testes. Responsible for the controlling of the production of sperm and, along with
ketotestosterone, the development of
characteristics. Included in feed given to some species during early developmental stages to produce all male stocks for future spawning use see
Order of fish (part of the superorder Acanthopterygii) includes fish such as
(Balistes), Pufferfish (Tetradon) and Boxfish (Ostracion)
Marine flagellate green algae. Used often in marine hatcheries. Larger than most other cultured algaes, (8-16 microns diameter), it is much easier to culture than some of the smaller algaes such as Isochrysis and Nannochloropsis.
Chemical which serves to heal or cure
A device consisting of two different metal wires, for
temperature measurement. One of the wires is exposed to the temperature to be
measured and the other is maintained at a known temperature. An electro motive force
(e.m.f.) is developed as a result and this can be read by an instrument in millivolts and converted into temperature units.
A plastic material that can be repeatedly softened through heating and hardened again on cooling. An example is
UPVC, which when heated, softens to enable moulding and welding, but on cooling hardens. If the finished product is not correct, the material can be heated, and manipulated again.
A plastic that is initially soft, but once changed to a rigid form (e.g. by heating), will not reverse back to the soft form on cooling. An example are the resin based
compounds that are used as adhesives, where once the reaction (involving heat) has taken place, they cannot be softened back to the liquid glue form again.
A device which controls the heating or cooling of a substance,
by turning machinery on or off, in order to maintain a constant temperature.
Rise and fall of the sea occurring twice each lunar day. See software link (freeware) for tide predictions for all areas of the world. Tides can affect aquaculture systems in a number of ways:
1. As tides rise and fall in sea lochs and fjords, currents can be formed which will allow good water exchange rates in cages, supplying dissolved oxygen to the fish and taking away waste products. If water velocities are too high, the cage net can be pulled at an angle (see net bagging), reducing the volume of the cage and damaging the fish.
2. Pump ashore systems can experience changing water quality between the tides. This is especially so with temperature and salinity. Where the high tide floods sand or mud flats that have been warmed by the sun, as the water draws back to low tide, temperatures on the farm can rise. Similarly where a river enters the sea near an inlet, low tides can result in lowering of salinity.
3. Tides are essential for the maintenance of some shellfish growing techniques. The window of low tide allows the farmer to inspect and work with the stock.
The distance from the snout to the tip of the tail. Not often used in farmed fish due to interferences associated with
erosion of the tail. Fork length is more commonly used, as this is largely independent of fin erosion.
The gradual adding of controlled and measured amounts of a substance (often a
reagent) into another (often the sample) to elicit a response. The measured amount added can then be converted into a value that denotes the concentration of a substance in the sample.
A state of apathy. Animals appear sluggish and
unwilling to exert energy.
The twisting of the body in development of gastropods.
The loss of water vapour by plants to the
atmosphere. Occurring mainly from leaves through pores, whose main function is the exchange of
oxygen and carbon
dioxide. Water lost through the leaves is replaced by a continual flow of water (and nutrients) up from the roots. Also sometimes refers to the cycle of the uptake of water by plants and subsequent loss to the air as water vapour through the leaves
The feeding of low value species such as mackerel,
anchovy and sand eel in a whole, chopped or minces form. The feeding of trash fish is carried out in many marine farms where either it represents a cheaper option than using pelleted diets, or the species will not feed on pelleted
diets (eg yellowtail (seriola
quinqueradiatia). Trash fish is losing popularity as a diet as commercially prepared diets become more readily available. The feeding of trash fish involves problems such as increased risk of introducing a disease organism, storage difficulties, consistency of quality
/ supply and fouling of the water.
The way in which chemicals are administered to stock depends on the chemical, the dose rate and the type of holding system they are in.
Common term for flukes in the Class Trematoda. Comprises of external (monogenetic) and internal (digenetic) parasites of vertebrates. Main species of concern for aquaculture are the eye flukes, see Diplostomum.
|Tri butyl tin oxide
(TBT) Chemical used in paints and other solutions to give an antifoulant property. Once often used in aquaculture for the treatment of nets, the chemical also affects wild populations of molluscs and crustaceans, living in the vicinity of cages and so is banned in some areas as a result of pressure form
environmental groups and fishermen.
A cell that has three sets of chromosomes. Such organisms with triploid cells rather than the usual
diploid (2 sets) are sterile. The production of triploids in some species is desirable as there is no loss of condition caused by the maturation processes. The
process of turning fish into triploid involves either heat, cold, pressure or chemical shocks during the period just after
fertilisation. The process only works on female fish; the male fish are only partially affected. The treated male fish are unable to
produce sperm, but still produce testes and all the secondary sexual characteristics which accompany this. Male parent fish for eggs to be subjected to triploidy treatment are not true males, but a result of feminisation techniques which ensures that there are no male
chromosomes in the parents. There are various method of inducing triploidy in Rainbow trout
and Atlantic Salmon and some of these are detailed in the table. Triploidy has also been used successfully with flatfish, common carp, channel catfish and tilapia
(Oreochromis aureus). Triploid flatfish, catfish and tilapia have been shown to perform better, however in rainbow trout, this is unproven and in mixed populations of triploid and normal diploid fish, the triploid fish are not as aggressive feeders as the diploid which outweighs most of the advantages gained.
Classification of organisms according to their feeding relationships
Tidal wave produced as a result of earthquakes and volcanoes. Such tidal waves are caused by relatively small wave heights in the deep oceans, which when hitting shallow reefs and continental shelves, increase to great heights.
Commonly called the "freshwater bloodworm" or "sludge worm". Species of oligochaete worm found especially in polluted waters. Indicated as intermediate hosts in some diseases such as tapeworms. Used by some aquarists as a live feed for their fish but have little value as feed in aquaculture.
The ability of light to penetrate through the water. Turbidity is caused by the sum of suspended solids particles and any dissolved chemicals in the water which may restrict the passage of light through the water. The most common method of measurement is by using Secci disc. Electronic meters are available for measuring, but these are only of use in aquaculture in green water systems as the sensitivity of the probes is generally not high enough for other waters. The turbidity of the water can affect aquaculture in a two ways ; 1.By limiting the feeding capabilities of sight feeders (such as salmonids), 2. By restricting the light available to algae and plants in the water, causing them to die off or limit growth. The treatment of turbid water is dependant on the nature of the particles or chemicals that are causing it.
A machine in which a fluid or a gas is used to produce a rotational motion. Most commonly used for generation of electricity. The most common turbines found in aquaculture are powered by wind or water. Wind turbines are useful for providing electricity in remote locations, especially for recharging battery packs for feeders, alarms etc. Wind turbines are flexible and can be easily relocated. Water powered turbines are used in some mountainous regions where farms have a supply from a body of water much higher than itself. The power generated by a turbine = head x flow (P=H x Q). On normal farm sites, water power is not commercially viable, for example a water turbine with a flow of 22,500m3/day with a 4.5m head will only generate about 7kW if used as a generator. If used as a direct drive for a pump it will produce the equivalent of 9kW. Small hydroelectric generators typically take between 3 and 5 years to pay for themselves, but this does not include the additional management and maintenance time of such a system.
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