The Aquarist’s Encyclopedic-Dictionary of Fish-Keeping

Article Index

µm: Symbol for the micrometer, also called a micron. One micrometer (micron) is one millionth of a meter or 1 x 10-6 meters in scientific notation.

Absorption: The diffusion of molecules into a solid or liquid. For example, medication in medicated foods is absorbed through the gut into the fish's bloodstream.

Acute: A disease which has a sudden onset, progresses quickly, and often runs its course quickly is characterized as "acute". Acute is the opposite of chronic.

Adsorption: The attraction of molecules to the surface of a solid or liquid. Aerobe: A bacterium which grows in the presence of the normal oxygen level of air (21% O2).

Anoxic: Oxygen deficient.

Archea: A diverse group of prokaryotes, distinct from bacteria. They often inhabit the Earth's most extreme environments such as hot springs and areas of extreme salinity and pH.

Aseptic: Aseptic means free of pathogens. The aseptic technique is a way of preparing cultures for use in diagnostic tests that prevents contamination from organisms in the air or on your skin.

Bacteria: A diverse group of prokaryotes.

Bactericidal: A group of antibiotics which actively kill bacterial cells.

Bacteriostatic: A group of antibiotics which slow bacterial reproduction so that the fish's immune system can overcome the infection.

Broad-Spectrum Antibiotic: Kills a wider range of bacterial cells. They are usually effective against both gram-positive and some gram-negative bacteria.

Capsule: a gelatinous coating outside of the cell wall for protection and adherence to the environment.

Cell Wall: a rigid layer surrounding the plasma membrane which gives the cell support against osmotic forces.

Chronic: A disease which is long-term is characterized as "chronic". Chronic is the opposite of acute.

Coccus: One of the common shapes of bacterial cells. Cocci (plural) are spherical.

Colony: An aggregate of bacterial cells which are all descendants of a single parent cell which underwent division.

Conjugation: the temporary joining of two bacterial cells and the movement of genetic material from one to the other.

Crystal Violet: a purple stain used in the first step of the Gram Stain procedure.

Cytoplasm: the interior region of the cell.

Differential Stain: a technique for staining cells where not all cells are stained the same color.

Endospore: a form of a bacterial cell which is highly resistant to heat, harsh chemicals, and even radiation. They can remain dormant for many centuries before returning to their reproducing state when conditions are right. Endospores can easily be spread by movement of air and water, or through animal feces.

Endotoxin: The term for a particular component of the LPS in gram-negative bacteria. Endotoxin is toxic to humans and animals and is responsible for the virulent symptoms of the infection.

Eukaryote: An organism whose cell(s) contain a nucleus and other membrane-bound organelles. Eukaryotic cells typically range from 2µm to 200µm in diameter, which is, on average, larger than prokaryotic cells.

Facultative Aerobe: A bacterium which will use oxygen if it is present, but can also grow in anoxic conditions.

Flagellum: an organelle which is used for locomotion.

Flora: Bacteria which are normally found on or in the fish's body, or in its environment.

Fungi: Eukaryotes which are defined by their method of obtaining food. They decompose organic matter outside of their cells and then absorb the nutrients.

Gram-negative: A classification of bacteria based on the Gram Stain reaction. Gram negative cells have a very complex cell wall with both an inner an outer membrane surrounding a thin, rigid layer of peptidoglycan. The outer membrane is composed of lipopolysaccharide, or LPS. It is a component of the LPS which serves as the "endotoxin" which causes the virulent symptoms of the infection. Gram-negative cells appear pink/red because during the gram stain reaction, alcohol penetrates the outer membrane, removing the crystal violet-iodine complex, allowing safranin (red) to stain the cell in the final step of the gram stain.

Gram-positive: A classification of bacteria based on the Gram Stain reaction. Gram-positive cells have a very thick, rigid layer of peptidoglycan without an outer membrane. Gram-positive cells appear purple because during the gram stain reaction, alcohol is unable to penetrate the thick layer of peptidoglycan. Thus the cell retains the crystal violet-iodine complex and is unable to take up the red safranin dye.

Gram Stain: A differential staining technique which is based on morphological distinctions between the cell walls of bacteria. Based on the Gram Stain, bacteria are classified as either gram-positive or gram-negative. Gram-negative bacteria are more commonly associated with aquarium diseases.

HUFA: an acronym for "Highly Unsaturated Fatty Acid". Such fatty acids tend to have 20 or more carbon atoms and play a very important role in fish nutrition.

Hydrophilic: a property of being attracted to water.

Hydrophobic: a property of being excluded by water. Hydrophobic interactions occur when hydrophobic molecule associate with one another, often in a droplet form, rather than with water molecules

Iodine: A stain which forms an insoluble complex with crystal violet in the gram stain reaction.

Microaerophile: A bacterium classified as an aerobe that grows in oxygenated environments with lower concentrations than that of air (or >21% O2).

Micrometer (µm): Symbol for the micrometer, also called a micron. One micrometer (micron) is one millionth of a meter or 1 x 10-6 meters (in scientific notation.)

Morphological: Having to do with structure or form.

Nitrogen Cycle Illustration

Nitrogen Cycle: (Image to Right) In our aquariums, it refers to the process by which toxic nitrogenous compounds are converted to relatively harmless nitrates. An established nitrogen cycle is the key factor for good filtration in our aquariums. It takes 4-6 weeks to establish naturally without adding the proper nitrifying bacteria to boost the process.

Nucleoid: The region of the cell containing the chromosome. This is not a membrane-bound area.

Nucleus: A large organelle found only in Eukaryotic cells which contains the genetic material of the cell. Prokaryotic cells lack a nucleus.

Opportunistic Pathogen: Often considered normal flora, they will not cause a normal fish to become sick. However, a fish which is immunocompromised due to stress, young or old age, malnutrition, or a preexisting disease can be attacked by these organisms.

Organelle: Specialized, membrane-bound structures found within eukaryotic cells. For example, the nucleus is an organelle.

Pathogenic: Disease-causing.

Peptidoglycan: The rigid component of bacterial cell walls which provides the strength needed to withstand the osmotic pressure which would otherwise cause the cell to burst.

Pilus: a structure used by bacteria to attach to exterior surfaces.

Plasmid: A small, circular segment of DNA which is separate from the bacterial chromosome (bacteria have only one long, circular chromosome). Plasmids carry genes not necessary for normal survival, but may be advantageous at certain times (such as genes for antibiotic resistance.) Plasmids can be transferred between bacterial cells.

Plasma Membrane: a selectively-permeable barrier which allows oxygen and nutrients in and waste products out.

Primary Pathogen: Will cause disease in normal, otherwise healthy fish.

Prokaryote: A unicellular organism whose cell lacks a nucleus and other membrane-bound organelles. They typically range from 0.2µm to 50µm in diameter, which is much smaller than eukaryotic cells. Bacteria fall into this category. *Note that while prokaryotes are almost exclusively unicellular, some will form cooperative aggregates of two or more cells.

Protist: Single-celled eukaryote. Algae is a term to describe photosynthetic protists.

Quarantine: A very strict isolation imposed on all new living additions to an aquarium. Read about the Angels Plus recommended Quarantine Procedure here.

Resistance-factor: A plasmid which contains genes that confer antibiotic resistance or the ability to resist other growth inhibitors to the bacterial cells which possess them.

Ribosome:  An organelle which is the site of protein synthesis. This organelle lacks a membrane.

Rod: One of the common shapes of bacterial cells. Rods are longer than they are wide.

Safranin: A counterstain used in the gram stain procedure which allows the gram-negative cells to appear pink/red.

Systemic: A disease which affects many areas of the body, and perhaps the entire body, is said to be "systemic".

Virulence: Is a measure of how many bacterial cells of a certain strain must be present in the host in order to elicit a response by the host in a certain amount of time. Another way of thinking about virulence is the ease with which bacterial toxins break down the tissues of the fish. Digestion of the fish provides nutrients that allow the bacteria to reproduce - increasing in number until they elicit a host response, occasionally, death. The ease with which they digest the host, determines how long this process will take. Virulence can also be though of as the severity of a disease.

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