accessory heart: a valved sac usually located in the caudal region and powered by contraction of skeletal muscle of the fish that helps move venous blood back to the heart. Hagfish have several accessory hearts one of which is comprised of actual cardiac muscle.

aerobic: oxygen requiring

Agnatha: a taxonomic designation. A superclass under subphylum Vetebrata, the agnathans are lampreys and hagfish. They are jawless and are the most primitive of living fishes.

affinity: with reference to hemoglobin, this is the ease with which the Hb loads oxygen. Hb with a high affinity for oxygen will load at a lower partial pressure while Hb with a lower affinity loads at a higher partial pressure.

alimentary canal : the entire digestive tube (mouth, esophagus, stomach and intestine) collectively.

anabolism: constructive metabolism, the building up of more complex organic molecules from simpler ones.

anoxic: without oxygen.

aquaculture: the growing of aquatic organisms for human needs, this includes fish farming.

ATP (adenosine triphosophate) : This is a high energy compound that serves the source of power for cellular work.

bolus: a small, lump or mass of substance, e.g. a meal of partially digested food in the digestive tract.

buccal cavity: the mouth cavity ahead of the gills, the space behind the gills is the opercular cavity.

capillary: the smallest blood vessels, just big enough for passage of red blood cells. It is in the capillaries that products diffuse in and out of blood.

carbohydrase: an enzyme that breaks down starches in the gut into simple sugars for absorbtion.

catabolism: destructive metabolism, the breakdown of organic molecules into simpler forms.

chondricthyan: a member of the class Chondricthyes, cartilagenous fishes. Living fish in the class are the sharks and rays.

covalent: the strong chemical bond created by electron sharing.

diurnal: over the course of a day, daily.

elasmobranchs: a taxonomic designation. The subclass of sharks and rays under class Chondricthyes.

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

emulsify: to make into an emulsion, a finely divided suspension of an oil in an aqueous mixture.

endocrine : secreting "into", typically from glandular tissue into the blood.

erythrocyte: red blood cell (RBC), the primary function of which is to contain hemoglobin that carries oxygen in blood.

estivation: an extended period of slowed metabolism.

euryhaline: a wide tolerance for environmental salinity, in other words, the ability to move from fresh water to salt water and back again.

exocrine: secreting "out of", typically from glandular tissue into the intestine.

fecundity: number of offspring. A highly fecund fish produces a large number of offspring.

filament: part of the gill, a paired series of filaments branch off each gill arch, each filament bears many lamellae where actual blood/water exchange occurs. Filaments are sometimes termed "primary lamellae".

gonadotropin: a pituitary hormone that stimulates the gonads.

glycogen: an insoluble carbohydrate formed by animals from glucose for storage of energy in liver and muscles, "animal starch".

glycolysis: the anaerobic pathway for the phosphorylation of ADP to ATP using glucose as an energy source. Glucose is transformed into pyruvate generating two ATP's. Under aerobic conditions, pyruvate can flow through the Krebs cycle with production of 12 more ATP's. In the absence of oxygen, pyruvate is converted to lactate.

glomeruli: (singular, glomerulus) the bundle of porous capillaries in vertebrate kidneys that pass water (and sugar and salts) into the kidney tubule to begin urine flow.

glomerular filtrate : the water and molecules (salts, glucose and small protein molecules) that pass through the glomerular capillaries into the kidney tubule.

gross: in the context of anatomy this refers to the whole, unmagnified view.

Haldane effect: named for a British physician, this describes the fact that deoxygenated Hb is a better proton acceptor than the oxygenated form. When Hb becomes oxygenated it releases hydronium ions driving H+ + HCO3 - toward CO2 + H2O.

heterocercal tail: a caudal fin that is asymmetrical in shape as opposed to the typical, symmetrical homocercal tail.

hematocrit: a measurement of the volume of the cells in blood. It is determined by centrifuging a small tube of whole blood until the cells separate from the plasma. The packed cell volume is expressed as a percent of the total blood volume.

hemibranch: one of the two series of filaments on a gill arch, "half gill".

hermaphroditism : having both sexes in the same individual.

histology: the study of cellular and sub-cellular view of tissue, in other words the microscopic view.

holobranch: both of the paired series of filaments on a gill arch, "whole gill".

holosteans: a taxonomic designation. An infraclass under the class Osteichthyes (bony fishes), holosteans are the gars and bowfin.

homeostasis: the maintenance of relatively stable conditions inside an organism despite a changing environment.

hybridogensis : a condition where mating between a female and male of a related species produces a hybrid, but the male genes are lost during meiosis, so each generation is all female.

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

hyperplasia: an increase in tissue mass caused by proliferation of cells resulting in more than the normal number of a given cell type.

hypoxic: with low oxygen

in vitro: a Latin term meaning "in glass". In physiology, it refers to facts determined in a test tube outside of a living organism. The converse term is in vivo, "in life" referring to findings from living animals.

kype: an extended jaw during spawning time, a male secondary sex characteristic of salmonid fish.

lamellae (plural): the part of the gill similar to a capillary where blood/water exchange occurs, many lamellae branch off each filament. Sometimes termed "secondary lamellae". The singular is lamella.

lamellar lacunae: the spaces inside the lamella in which blood can flow.

lipase: an enzyme that breaks down fats and oils in the gut into smaller units for absorbtion.

lumen: the inside of a hollow structure.

myotomes: the bundles in which the white muscle of fish is arranged.

neurons: nerve cells.

: chemical compounds that act as local messengers to transmit nerve signals across synapses.

obligate: must follow a certain way of life, as opposed to facultative which may or may not follow that way of life, e.g. tigers are obligated carnivores while humans are facultative carnivores.

oral valve: fish that have a respiratory pump have flaps behind each lip that act as a one way valve when the mouth is closed, preventing back flow of water out the mouth. Similarly, the opercula have a flap on the rear that seals the opercular opening during opercular expansion.

osmosis: the movement of water through a semipermeable membrane. If the water on one side of the membrane has more dissolved solids, the water will tend to move in that direction until the two sides are equally dilute.

osmotic pressure: a measure of the tendency for water to move across a semipermeable membrane because of osmosis.

otoliths: literally "ear stones", small bits of bone found in the inner ear, some aid in hearing and others in gravity (which way is up?) detection.

oviparous: egg-laying.

ovoviparous: the egg is retained in the mother's body until hatching, but the female doesn't supply any nutrients to the embryo, only oxygen. The embryo develops on the energy in the yolk.

parthenogenesis: a form of asexual reproduction where an all-female race requires sperm from a closely related species to trigger development of the egg, but no genetic material from the male is incorporated into the offspring.

partial pressure: the physical pressure of oxygen on the surface of the water. It is termed "partial" because it is usually a fraction of the total gas pressure in a mixture of gases.

pelagic: open water dwelling.

pheromone: a chemical substance that an animal makes to communicate outside the body, as opposed to a hormone that is used for internal communication.

pineal: a gland in the top of the head that is often a light receptor and secretes melatonin. Implicated in perception of day length.

pinocytosis: the actual physical engulfing of water or small particles by cell walls.

pituitary: or hypophysis, a gland under the brain and connected to the hypothalmic region that produces many hormones in response to signals from the brain. Sometimes referred to as the "master gland".

planktivorous: feeding on plankton, small floating plants (phytoplankton) often too small for fish and, more commonly, floating invertebrate animals (zooplankton).

plasma: the non-cellular component of blood, it contains water and water soluble proteins such as albumin and globulins.

poikilothermic: not body heat regulating, i.e. cold blooded.

portal system: a circulatory feature where blood is carried from one capillary bed to another by a larger vein.

protease: an enzyme that breaks down protein in the gut into amino acid sequences for absorbtion.

pulmonary: having to do with the lung.

ram ventilation: when the fish or the water is moving rapidly, the fish may ventilate by simply opening its mouth and allowing water to be forced across the gill and out its mouth.

rete mirabile: (reet meer-ROB-ill-lee) a German phrase, literally "wonder net" referring to a countercurrent system where many efferent and afferent capillaries run parallel to each other as they enter and leave the gas gland.

rods and cones : the light sensitive cells of the retina. They contain light absorbing pigments and the absorbed light energy triggers a nerve impulse to the brain. Rods function at lower light and cones detect different wavelenghs (color).

ruminant : having a specialized digestive tract that allows an animal to digest cellulose with the aid of bacteria.

sacculation: convoluted development of tissue to develop many sacs or pockets.

sigmoid: S-shaped from the Greek letter "S", sigma.

solubility: the amount of oxygen that water can hold in simple solution. This varies according to temperature (warm water can hold less O2 than cold water) and dissolved solids (salt water can hold less O2 than fresh water).

solute: substances that are in solution, e.g. dissolved salt.

spawning tubercles: bony protrusions on the skull during spawning time, a male secondary sex characteristic of some (e.g. minnows) fish

specific heat: the amount of heat it takes to warm a substance. Water has a specific heat of 1.00 meaning it takes 1 calorie to heat one gram of water 1o C (or a gram of water must lose 1 calorie to decrease 1o ). This more than earth or stone and much more than air.

sphincter: a circular muscle that closes off an orifice upon contraction.

sympatric: sharing the same range.

: the tiny gap between neurons or between neurons and muscle cells across which nerve signals must travel by means of neurotransmitters.

teleosts: a taxonomic designation. An infraclass under the class Osteichthyes (bony fishes), teleosts are the modern, bony fishes.

viviparous: live-bearing where, unlike ovoviparity, the female supplies nutrients to the developing embryos.