aerobic: requiring oxygen.

alkalinity: a measure of the buffering capacity of water that is measured by titrating acid into a sample until the pH changes. Expressed as mg/L as CaCO3.

anaerobic heterotrophs: heterotrophs are any organisms that require a food source (as opposed to green plants that are autotrophs). Anaerobic means without oxygen. Anareobic heterotrophs use a food source for energy, but do so in the absence of oxygen.

anoxic: without oxygen.

aquaculture: raising aquatic animals in a captive situation like farm animals, usually for food.

artesian well: a well drilled until it reaches a pressurized strata of water that brings it to the surface without pumping.

atrophies: to waste away, wither, or deteriorate.

carbonic anhydrase: an enzyme that catalyzes the reaction of carbon dioxide with water to form carbonic acid. By facilitating this reaction in the lamellar blood, fish are able to maximize the partial pressure gradient of carbon dioxide between the blood and water.

catabolism: metabolic breakdown. When animals catabolize protein, they enzymatically cleave the amino groups on amino acids and the free aminos pick up a hydrogen molecule forming ammonia.

colloids: very small, insoluble particles larger than molecules, but so small they remain suspended in water.

countercurrent: A countercurrent system places the water with the lowest oxygen pressure in contact with the blood with the lowest oxygen pressure. This maintains the greatest pressure gradient possible over the entire blood/water interface maximizing the flow of oxygen into the blood.

covalently: chemically bound as a result of the sharing of a pair of electrons.

deamination: when protein is catabolized, some amino groups (NH2) in the amino acids are removed, this is what forms ammonia.

denitrification: the process in which bacteria convert nitrate (NO3) into gaseous nitrogen (N2).

diffusion: the spreading out from an area of higher concentration to an area of lower concentration by molecular movement.

embolism: a blockage of a blood vessel by a bit of foreign matter (bubble, blood clot, etc.).

essential amino acids: of the 20 commonly occuring amino acids ten are essential for growth. The others can be synthesized by the liver, if they do not occur in the diet.

facultative: having the ability to live under other than the ususal. Facultative anaerobes may live with or without oxygen.

fecund: having the ability produce numerous offspring.

gas bubble disease: if supersaturated nitrogen enters a fish's blood stream over the gills bubbles of gas can form in the circulatory system resulting in embolisms and death. This same condition results in "the bends" in human divers.

hardness: a water quality characterisitic originally defined as the ability of water to precipitate soap. Now defined as the sum of the divalent cations of magnesium (Mg++) and calcium (Ca++) expressed as mg/L as CaCO3.

hydrostatic pressure: the pressure (weight) exerted by a column of still water.

hypoxic: with low oxygen.

inert: not readily reactive with other elements; forming few or no chemical compounds.

kPa: kilopascal, a unit of measurement for pressure in the International System of Units (SI), symbolized by kPa. The conversion factor from lb/in2 to kPa is 6.9 kPa per lb/in2 (psi).

lamellae: plural of lamella, the plate-like tissues in a fish's gills that are the sites of gas exchange.

leach field: an area designed to promote percolation of liquid waste into the soil. It can involve buried pipes with holes laid over gravel filled trenches like a septic tank system or the gravel bed may be on the surface.

molar equivalent: essentially this means that two amounts are equal, not in weight or volume, but in number of molecules.

obligate: requiring. Obligate aerobes require oxygen.

off gas: Gas that is released from the water. When using pure oxygen, this refers to the oxygen that is not absorbed during the transfer method and can be recycled before it is lost to the atmosphere.

partial pressure: the physical pressure of oxygen on the surface of the water. It is termed "partial" because it is a fraction of the total gas pressure of the air. Partial pressure is what moves oxygen from the water into the fish.

pathogen: a disease causing agent, i.e. parasite, bacterium, or virus.

pH: is the negative log of the hydrogen ion (H+) concentration. Practically, it is used as a measure of the acidity or alkalinity of a solution with a range of 0 (acid) to 14 (basic), with 7 neutral.

porosity: having pores or openings. In solids removal, the size of the pores determines the size of particles removed.

sac fry: after fish eggs hatch, the somewhat immobile embryos live for a week or so on stored food in their yolk sac, after absorbing this nutrition they begin to feed and become free living.

solenoid: an electro-magnetic switch that is capable of controlling mechanical operations electronically.

standpipe: a vertical drain pipe that maintains a given water level as water spills over into the top.

sump tank: the lowest point to which water flows in a recirculation unit before it is pumped up through the system again.

titrated: measuring how much of a substance it is necessary to add to a solution in order to produce a given reaction.

terrestrial: living or growing on land; not aquatic.

weirs: dams placed across a body of water to regulate water flow. Used in aquaculture operations to slow flow in settling tanks, allowing large particles to settle to the bottom for removal.