Koi Health Glossary
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Koi Health Glossary


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Here are some common terms to help you in understanding your Fish's Health.


  • ABCESS Localized collection of pus in any part of the body which is the result of the disintegration or displacement of tissue and is frequently associated with swelling and other signs of inflammation. Abscesses are usually produced by microorganisms.
  • ABRASION Scraping away of the outer layers of the skin of a mucous membrane usually as a result of injury.
  • ACUTE Clincal sign of a disease that has rapid onset, severe symptoms and a short course. Opposite of chronic.
  • ADENOMA An often benign neoplasm of epithelial tissue where the tumor cells form gland-like structures; usually well circumscribed and generally compresses rather than invade surrounding tissue.
  • ADENOSINE TRIPHOSPHATE Abbrev. ATP. An adenosine-derived nucleotide, C10H16N5O13P3, that contains high-energy phosphate bonds and is used to transport energy to cells for biochemical processes.
  • AEROBIC Organism that lives only in the presence of oxygen.
  • ALKALINITY Measures the buffering capacity of water which can be thought of as the sensitivity of pH. It is measured as calcium carbonatee equivalents in parts per million (ppm) or milligrams per liter (mg/l). While 100 ppm is considered ideal, readings from 50-200 are acceptable. Anything below 50 warns that a ph Crash is imminent. See also: parts per notation.
  • AMINO ACID Abbrev: AA. Large group of organic compounds marked by the presence of both an amino (NH3) and carboxyl (COOH) group. They are the building blocks from which proteins are built and are the end products of protein digestion or hydrolysis. See also: ammonia, hydrolysis, organic, protein.
  • AMMONIA Unionized or free ammonia, NH3. An alkaline gas formed by decomposition of nitrogen-containing substances such as proteins and amino acids. Ammonia is converted into nitrogenous waste that is excreted from koi gills and also results from the decomposition of solid waste and organic material in the pond. It is the toxic component of total ammonia, which is the measurement of most ammonia test kits. As such it acts as a pollutant that is highly toxic to koi. See also: amino acid, bacterium, ionized, nitrate, nitrite, nitrogen, nitrogenous waste, organic, pollution, protein, toxic.
  • ANAEROBIC Organism that lives in the absence of oxygen.
  • ANOXIA Total lack of oxygen. This word and hypoxia are often misused. See also: hypoxia.
  • ANTIBODY Complex glycoproteins, produced by B lymphocytes in response to an antigen. All antibodies are created by B-Cells linking with a foreign antigen on the surface of an invading organism. It is an important component of the acquired immune response. See also: antigen, B cell, immune response, protein.
  • ANTIGEN A protein marker on the surface of cells that identifies the type of cell, stimulates the production of antibodies and cytotoxic responses. Reactions to antigens by T and B cells are part of the specific immune response. Generally refers to the vaccine or pathogen causing the reaction. See also: antibody, B cell, cell, cytotoxic, immune response, pathogenic, protein, T cell.
  • ANTISEPTIC A substance that inhibits the growth and reproduction of disease-causing microorganisms.
  • AQUALCULTURE The production of aquatic organisms (plant and animal) for food, aquarium, or scientific purposes, generally as a commercial venture.
  • ASEPTIC Free of pathogenic microorganisms (aseptic surgical instruments) or the use of methods to protect against infection by pathogenic microorganisms (aseptic surgical techniques).
  • AUTOLYSIS The digestion of cells by enzymes present within them. The cells most susceptible to autolysis tend to be dead or dying cells.
  • AUOTROPHIC Organisms and green plants that are self-nourishing and grow in the absense of organic compounds. Plants are photosynthetic and organisms are chemosynthetic.
  • B-CELL Lymphoid stem cells from hemapoietic tissue that migrate to and become mature antigen-specific cells in the spleen.
  • BACTERIUM Typically these are unicellular microorganisms whose shape ranges from spheres to rods to spirals. Some are pathogenic to koi, others are beneficial, e.g. for the biological conversion of ammonia to nitrate and for the decomposition of organic matter.
  • BUCCAL CAVITY The mouth cavity.
  • CARBONIC ANHYDRASE Enzyme which aids carbon dioxide transport and release by catalyzing the synthesis, and the dehydration, of carbonic acid from, and to, carbon dioxide and water. Koi facilitate this reaction in the lamellar blood of the gills and are able to maximize the partial pressure gradiend of carbon dioxide between the blood and the water.
  • CATABOLISM The metabolic breakdown of complex molecules into simpler ones, often resulting in a release of energy. When koi catbolize protein, they enzymatically cleaino acids and then the free aminos pick a hydrogen molecule, thus forming ammonia.
  • CELL Mass of protoplasm containing a nucleus or nuclear material. Cells and their products make up all the tissues of the body. All the functional activities of the body are carried out by cells. Their structure and form are closely correlated with their function.
  • CHRONIC Persistent disease that is progresses slowly and shows change slowly. Opposite of acute.
  • CILIA Microscopic hairlike process that extends from the surface of a unicellular organism and acts in unison with like structures to cause movement.
  • CLINICAL The outward appearance of a disease in a living organism based on actual observation and treatment as apposed to experimentally or pathologically. See also: acute, disease, inflammation, pathological condition.
  • COLLOID Particulate matter, finely divided and insoluble but larger than molecules that are dispersed within a pond in such a manner as to prevent them from being filtered easily or settled rapidly.
  • COMMUNICAL DISEASE Disease that may be transmitted directly or indirectly from one organism to another. See also: disease, quarantine.
  • CONGESTION Excessive accumulation of blood or tissue fluid within an organ or peripheral blood vessel.
  • CUTICLE Often used as synonymn for the glycocalyx.
  • CYTOTOXIC Destroys cells.
  • DEAMINATION When a protein is catabolized, some amino groups (NH2) in the amino acids are removed, forming ammonia.
  • DEBRIDE Surgically excise dead, devitalized tissue and removal of foreign matter from a wound.
  • DENITRIFICATION Process by which denitrifying bacteria convert nitrate (NO3) into the gaseous form of nitrogen (N2).
  • DETRITUS Decomposing organic matter in a pond or filter. See also: organic.
  • DIFFUSE To be scattered widely throughout a tissue or substance vs localized or focal. As apposed to focal.
  • DISEASE A pathological condition that presents a group of clinical signs and symptoms that set the condition apart as abnormal and different from other normal or pathological body conditions.
  • DIURNAL Something that occurs each day. Syn: daily.
  • DUCK Narrow tubular vessel or channel that conveys secretions from a gland. See also: exocrine, gland, secretion.
  • EMBOLISM Obstruction or occlusion of a blood vessel by a detached thrombus, air or foreign body.
  • ENDOCRINE Gland that secretes directly into the bloodstream.
  • ENZYME Organic catalyst produced by living cells but capable of acting independently. They are complex proteins that induce chemical changes in other substances without being changed themselves. They are reaction-specific acting in just one way and can accelerate the speed of a chemical reaction.
  • EPIDERMIS The outer layer of skin.
  • EPITHELIUM Layer of cells forming the epidermis of the skin and the surface layer of mucous and serous membranes. The cells rest on a basement membrane and lie in close approximity to each other with little intercellular material.They may be flat (squamous), cubed (cuboidal) or cylindrical (columnar). It serves to protect and lubricate.
  • EPIZOOTIC Any infectuous disease that attacks many animals in the same geographical area in a short period of time.
  • ERYTHEMA Macculary, diffused redness of skin.
  • EXOCRINE Glands whose secretions reach an epithelial surface either directly or through a duct. See also: duct, epithelium, gland, pancreas, secretion.
  • EXUDATE Substances which penetrate through vessel walls into adjoining tissue or into a cavity producing pus or serum. There are more cells, protein, lactic dehydrogen and solid material than in a transudate.
  • FACULATIVE Ability to live under more than one specific set of environmental conditions; e.g. a faculative aenerobe may live with or without oxygen.
  • FIBRIN Whitish filamentous protein formed by the action of thrombin on fibrinogen. See also: inflammation, protein.
  • FOCAL Area of concentration or immediate attention. As apposed to diffuse. See also: diffuse.
  • FURUNCLE An encycted locus of baterial infection often referred to in the vernacular as a boil.
  • GILL FILAMENT A paired series of filaments that branch off of each gill arch. Each filament contain numerous lamellae and are often referred to as 'primary lamella'.
  • GILL LAMELLAE (Sing: lamella) Each gill filament has many lamellae brancing off and is where blood/water exchange occurs. When filaments are referred to as primary lamellae, these are generally called 'secondary lamella.
  • GLAND Organ or structure made up of an aggregation of cells that manufacture a secretion discharged to and used by some other part of the body. Glands can be: by structure -- simple or complex; by secretion -- mucous, serous or mixed; by ducts -- exocrine or endocrine; by shape -- tubular, saccular; by lumen -- alveolar, acinar; and by formation of secretions -- merocrine, apocrine, holicrine.
  • GLYCOCALYX Slimy mucous layer of mucoplysaccharide, glycoproteins and sloughed epidermal cells. It contains enzymes (lysozymes) and antibodies (immunoglobulins) which can kill invading organisms. So it is both a mechanical and chemical barrier and is the koi's first line of defense against pathogens.
  • HEMAPOIETIC Blood formation.
  • HEMORRHAGE Abnormal, severe internal or external discharge of blood from blood vessels.
  • HETEROTROPIC Organism that obtain energy from complex organic food versus plants which synthesize food from inorganic compounds.
  • HOMEOSTIS Maintenance of relatively stable conditions inside an organism despite a changing environment.
  • HOST Organism from chich a parasite obtains its nourishment.
  • HYDROLYSIS Chemical decomposition in which a substance is split into simpler compounds by the addition of water.
  • HYPEREMIA An unusual amount of blood in a tissue or part. Often a red area on skin that disappears on pressure.
  • HYPERPLASIA Excessive increase in the normal number of cells in a tissue or organ.
  • HYPERTROPHY Abnormal enlargement of the individual cells of an organ or tissue that does not involve tumor formation.
  • HYPOXIA Oxygen deficiency. This word and anoxia are often confused.
  • IMMUNE RESPONSE Reaction of the body to eliminate foreign antigens and prevent damage.
  • INFECTION Invasion and multiplication of pathogenic microorganisms (bacteria or virus) in tissues. Localized infection is normally accompanied by inflammation, but there can be inflammation when there is no infection present.
  • INFESTATION Invasion of tissue by animal parasites (protozoa, helminths and anthropods).
  • INFLAMMATION Non-specific immune response that occurs as a result of any type of bodily injury. In koi, the reaction of the tissues to injury characterized clinically by swelling and redness. Pathologically, by vasodilatation, hyperemia, accumulation of leucocytes, exudation of fluid and deposition of fibrin. See also: clinical, exudate, fibrin, hyperemia, immune response, infection, leucocyte, pathogenic, pus, tissue.
  • INORGANIC Chemical compounds not containing carbon. As apposed to organic.
  • INSULIN Polypeptide hormone produced by the β cells of the islets of Langerhans in the pancreas, which decreases the amount of glucose in the blood by stimulating its uptake by cells.
  • INTRAMUSCULAR Within a muscle.
  • IONIZED The dissociation of compounds (acids, bases and salts) into their constituent ions, e.g.the ionized (NH4-) form of ammonia, which is less toxic to koi than the unionized form.
  • LEUCOCYTE White or nonpigmented blood cell.
  • LYSIS Dissolution or destruction of cells, i.e. blood cells or bacteria, as by the action of a specific lysin that distrupts the cell membrane.
  • METABOLISM Sum af all physical and chemical changes within an organism and all energy and material transformations within its cells. It involves two fundamental processes: assimilation (a building-up process) called anabolism and disintegration (a tearing-down process) called catabolism.
  • METHEMOGLOBINEMIA Hemoglobin is poisoned by nitrite and forms methemoglobin and thus cannot carry oxygen. Methemoglobinemia is also called "brown blood disease".
  • MICROORGANISM Microscopic living organisms, especially a bacterium or a parasite.
  • MILT White solution that contains the spermatozoa (semen) of a male koi.
  • MORIBUND Organism dying from a disease.
  • MUCIN Glycoprotein found in mucus.
  • MUCOUS MEMBRANE Membrane that lines passages and cavities that communicate with the outside of the body. Consists of a surface layer of epthelium, a basement membrane and an underlying layer of connective tissue, the lamin propria. Mucus-secreting cells or glands are usually present. See also: abrasion, epithelium, gland, mucus.
  • MUCOUS A viscous (thick, gummy) fluid secreted by mucous membranes and glands consisting of mucin, leucocytes, inorganic salts, water and epithelial cells.
  • NECROSIS Pathologic death of one or more cells or a portion of tissue or organ, resulting from irreversible damage.
  • NECROSISNEOTENIC Organism that never reaches its adult stage but reproduces in its larval form.
  • NITRATE Chem Formula: NO3. The end product of biological conversion of e ammonia to nitrite and nitrite to nitrAte. It is not considered toxic to koi except in extremely high concentrations.
  • NITRITE Chem Sym:NO2. Intermediate nitrogenous compound formed in the process of bacteriological conversion of ammonia to nitrate. Very toxic to koi.
  • NITROGEN Chem Sym:N2. Elemental gas making up approximately 80% of the earth's atmosphere.
  • NITROGENOUS WASTE Organic waste with a high nitrogen content, e.g. animal manure, urine.
  • OPERCULAR CAVITY Space immediately behind the gills and covered by the opercular plate or flap which can be seen to move as the fish respires.
  • OPERCULUM The bony plate that covers the gills.
  • ORGAN Somewhat independent body part that performs a specialized function, e.g. pancrease.
  • ORGANIC Chemical substances containing carbon. As apposed to inorganic.
  • OSMOSIS Movement of a solvent through a semipermeable membrane from a solution of lower to higher concentration of the solutes.
  • OVUM Female reproductive or germ cell that is capable after fertilization of developing into a new organism of the same species. See also: zygote.
  • OXIDATION When a chemical substance combines with oxygen.
  • PANCREAS A gland of the endrocrine system that lies in the coelomic cavity. Scattered throughout its tissue are differentiated masses of cells that are islets of Langerhans. The pancrease produces both exocrins (digestive juices) and endocrins (insulin and glucagon).
  • PARASITE An organism that lives at the expense of, or in, or on another organism (the host) and which depends on the host for its metabolism.
  • PARTS PER NOTATION Various measures used with a number to indicate the concentration of one substance to another and often used when expressing the addition of a chemical to the pond. They are parts per: hundred (pph), thousand (ppt) and million (ppm). The relationship of the various "parts per" measure: 0.01 = 1 per 100 = 1 % = 1 pph (or 1 drop per 5 ml) = 10 ppt (or 10 mg/ml) = 10,000 ppm (or 10,000 mg/l).
  • PATHOGENIC Producing disease or pathological changes. See also: antigen, bacterium, infection, inflammation.
  • PATHOLOGICAL CONDITION A deviation from a normal condition associated with disease.
  • PERITONEUM Membrane that lines the walls of the abdominal cavity and folds inward to enclose the visera.
  • PHENOTYPE Physical appearance or makeup of an organism.
  • PHYLOGENCY Evolutionary development (the history) of species.
  • POLLUTION The introduction of substances, by direct or indirect human activity, into the environment resulting in toxic effects on living organisms. See also: ammonia, toxic.
  • POLYMERASE CHAIN REACTION Abbrev:pcr. Method for multiplying small amounts of DNA in quantities sufficient for the determination of identifying DNA sequences. Used as a diagnostic lab test for Cyprinid herpesvirus 3 (CyHV-3); commonly known as koi herpesvirus or KHV.
  • PROTEIN One class of complex nitrogenous compounds occuring naturally and that provide amino acids essential to the growth and repair of tissue.
  • PUS Liquid product of inflammation and composed of albuminous substances, a thin fluid and leucocytes
  • QUARANTINE Practice of isolating new or sick koi or ones exposed to a communicable disease in a separate pond or tank for a period equal to the longest incubation period of a disease.
  • ROE Eggs in the abdominal cavity of a female koi.
  • SECRETION Substance produced by glandular organs.
  • SEPTICEMIA Presence of living, reproducing bacteria in the blood stream. If allowed to progress, the bacteria may cause an overwhelming infection and death. See also: bacterium
  • SEROUS MEMBRANE Membrane lining a serous cavity.
  • SERUM Any serous fluid, especially that lubricating a serous membrane.
  • SQUAMOUS Scale-like tssue pattern. See also: epithelium, tissue
  • STRESS Sum of all biological phenomena that result from forces that disrupt equilibrium or produce strain. When stress is above the koi's tolerance level it will produce a pathological change. See also: pathological condition.
  • SUBCUTANEOUS Beneath the layer of the skin. SYN: hypodermic.
  • SYMBIOSIS Two organisms of different species living together in close association. Different associations may exist: neither harm each other (commensalism); beneficial to both (mutualism); one harmed, other benefited (parasitism). See also: parasite.
  • TELANGIECTASIS A vascular lesion (clot) when the capillaries of the gill lamellae dilate and the red blood cells begin to pool forming microthrombi.
  • TISSUE Aggregation of similar cells and their intercellular substance that together perform a particular, specialized function(s). See also: abcess, cell, congestion, diffuse, exudate, hyperemia, hyperplasia, hypertrophy, infection, inflammation, squamous.
  • TRANSUDATE Fluid that passes through a membrane, See also: exudate.
  • VIRULENCE Relative power and the degree of pathogenicity of a microorganism to cause disease in a koi. See also: microorganism, pathological condition.
  • VISERA Internal organs enclosed within a cavity. See also: organ
  • ZOONOSES Disease that can be transmitted from animal to human under natural conditions. See also: disease.
  • ZYGOTE Fertilzed ovum. See also: ovum.


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