Aquatic Veterinary Medicine – Water Quality Vocabulary

A comprehensive set of vocabulary flashcards covering essential terms, parameters, contaminants and management concepts related to aquatic water quality and fish health.

Water Quality

Measurement of physicochemical (abiotic) and microbiological (biotic) parameters that influence aquatic animal health.

Abiotic Parameters

Non-living water factors such as temperature, pH, dissolved oxygen, ammonia, nitrite, nitrate, alkalinity, hardness, salinity and turbidity.

Stocking Density

Number of animals per unit volume; high values raise waste, ammonia, oxygen demand, stress and disease risk.

Ectotherm

Animal whose body temperature fluctuates with environmental temperature (e.g., fish).

Temperature Stratification

Layering of water at different temperatures in deep ponds/lakes, potentially causing oxygen turnover events.

Dissolved Oxygen (DO)

Amount of free oxygen in water expressed in mg L⁻¹; essential for respiration.

Oxygen Saturation

Percentage of water’s maximum oxygen-holding capacity at a given temperature and pressure.

Gas Bubble Disease

Pathology from supersaturated water where microbubbles lodge in eyes, gills or skin.

Oxyhemoglobin Dissociation Curve

Graph showing relationship between blood oxygen saturation and partial pressure; shifted by temperature and pH changes.

pH

Negative log of hydrogen-ion concentration; scale 0–14 with 7 neutral,

Hydrogen Sulfide (H₂S)

Toxic gas produced under anaerobic conditions; smells like rotten eggs and impairs respiration/osmoregulation.

Alkalinity (Carbonate Hardness, KH)

Concentration of bicarbonate/carbonate ions that buffer pH against rapid change, expressed as mg CaCO₃ L⁻¹.

General Hardness (GH)

Total divalent cations (mainly Ca²⁺, Mg²⁺); important for skeletal and shell formation.

Buffering Capacity

Water’s ability to resist pH change, governed primarily by alkalinity.

Nitrogen Cycle

Conversion of ammonia → nitrite → nitrate by nitrifying bacteria and eventual removal via denitrification or plants.

Total Ammonia Nitrogen (TAN)

Sum of unionized ammonia (NH₃) and ionized ammonium (NH₄⁺) measured by test kits.

Free Ammonia Nitrogen (FAN / Unionized Ammonia, UIA)

NH₃ portion of TAN; ~100 × more toxic to fish than NH₄⁺.

Ammonia Toxicity

Gill damage, neurologic signs, ‘ammonia burns’ and death caused by elevated NH₃.

Nitrite

Intermediate nitrogen compound (NO₂⁻) that oxidizes hemoglobin to methemoglobin, causing brown blood disease.

Brown Blood Disease

Condition where nitrite converts hemoglobin to methemoglobin, hindering oxygen transport and causing hypoxia.

Nitrate

Relatively nontoxic end product (NO₃⁻) that accumulates and suppresses growth and appetite at high levels.

Denitrification

Bacterial conversion of nitrate to nitrogen gas, removing nitrogen from water.

Biofilter

Filter component housing nitrifying bacteria that perform biological nitrification in RAS, ponds, aquaria.

Biofilter Cycling

Maturation phase (2–6 weeks) during which nitrifying bacteria colonize media and establish the nitrogen cycle.

New Tank Syndrome

Toxic spikes of ammonia/nitrite in an immature system before biofilter is established.

Old Tank Syndrome

Chronic low alkalinity and dropping pH in neglected systems, destabilizing nitrification and raising TAN.

Recirculating Aquaculture System (RAS)

Closed system where water is mechanically and biologically filtered and reused.

Mechanical Filtration

Removal of solid particles via screens, drum filters, foam or socks before biofiltration.

Protein Skimmer

Saltwater device that removes organic compounds by forming foam and collecting surface-active waste.

Titrimetric Kit

Chemical test that uses titration to quantify water constituents like DO, KH, GH.

Colorimetric Kit

Reagent test where color change is compared visually or with a photometer to determine concentration.

Electronic Probe

Digital sensor (e.g., for pH, DO, salinity) providing rapid, loggable readings requiring regular calibration.

Ammonia Alert Badge

Color-changing in-tank indicator that continuously monitors TAN/FAN levels.

Salinity

Total dissolved ions expressed in ppt; freshwater < 2 ppt, brackish 2–16 ppt, seawater ≈ 35 ppt.

Total Dissolved Solids (TDS)

Sum of all ions and small organic molecules (<2 µm) in water; measured with conductivity probes.

Refractometer

Optical device that measures salinity based on light refraction through water.

Turbidity (Water Clarity)

Cloudiness caused by suspended particles; affects light penetration, gill health and species adapted preferences.

Eutrophication

Nutrient enrichment leading to dense algal growth and potential oxygen depletion.

Harmful Algal Bloom (HAB)

Algal proliferation that releases toxins, depletes oxygen or physically harms aquatic organisms.

Cyanobacteria

Photosynthetic bacteria capable of forming HABs; may produce hepato-, neuro- or dermatotoxins.

Chlorine

Strong oxidizer used to disinfect water; toxic to fish above 0.03 mg L⁻¹.

Chloramines

Stable chlorine-plus-ammonia compounds used in municipal water; persist longer and harm fish.

Sodium Thiosulfate

Chemical neutralizer of chlorine/chloramine (≈7.4 mg per 1 mg Cl₂).

Chloride Ion (Cl⁻)

Natural anion important for osmoregulation; distinct from toxic chlorine gas.

Heavy Metals

Toxic elements (e.g., lead, mercury, cadmium) that bioaccumulate and damage vital organs.

Bioaccumulation

Build-up of contaminants within an organism over time.

Biomagnification

Increase of contaminant concentration up the food chain.

Copper Toxicity

Fish distress or mortality from elevated Cu; also used therapeutically against parasites.

Zinc Toxicity

pH-dependent Zn poisoning from galvanized runoff; worsens in soft, acidic water.

Osmoregulation

Physiological process maintaining internal ion and water balance; energy cost rises outside optimal salinity.

Stress (in Fish)

Physiological state from adverse conditions causing immune suppression, poor growth and disease.

Liming Agents

Substances like agricultural limestone or coral that raise alkalinity and stabilize pH.

Baking Soda (Sodium Bicarbonate)

Common alkaline buffer added to increase KH (>100 mg L⁻¹) and support nitrification.

Phytoremediation

Use of plants to absorb excess nutrients (e.g., nitrate) from aquatic systems.

Supersaturation

Condition where dissolved gas exceeds 100 % saturation, risking gas bubble disease.

Calibration

Regular adjustment of probes/meters against standards to ensure accurate readings.

Test Strip

Quick, less reliable dip-and-read tool for multiple parameters; not recommended for precise work.