492 FISH HATCHERY MANAGEMENT 



Perivitelline Space Area between yolk and chorion of an egg where 

 embryo expansion occurs. 



Permanganate, Potassium KMnO,; strong oxidizing agent used as a 

 disinfectant and to control external parasites. 



Petechia A minute rounded spot of hemorrhage on a surface, usually 

 less than one millimeter in diameter. 



pH An expression of the acid- base relationship designated as the loga- 

 rithm of the reciprocal of the hydrogen-ion activity; the value of 7.0 

 expresses neutral solutions; values decreasing below 7.0 represent 

 increasing acidity; those increasing above 7.0 represent increasingly 

 basic solutions. 



Pharynx The cavity between the mouth and esophagus. 



Phenotype Appearance of an individual as contrasted with its genetic 

 makeup or genotype. Also used to designate a group of individuals 

 with similar appearance but not necessarily identical genotypes. 



Photoperiod The number of daylight hours best suited to the growth 

 and maturation of an organism. 



Photosynthesis The formation of carbohydrates from carbon dioxide 

 and water that takes place in the chlorophyll-containing tissues of 

 plants exposed to light; oxygen is produced as a by-product. 



Phytoplankton Minute plants suspended in water with little or no capa- 

 bility for controlling their position in the water mass; frequently 

 referred to as algae. 



Pig Trough See Von Bayer Trough. 



Pigmentation Disposition of coloring matter in an organ or tissue. 



Pituitary Small endocrine organ located near the brain. 



Planting of Fish The act of releasing fish from a hatchery into a 

 specific lake or river. Synonyms: distribution; stocking. 



Plasma The fluid fraction of the blood, as distinguished from corpuscles. 



Plasma contains dissolved salts and proteins. Compare with Serum. 

 Poikilothermic Having a body temperature that fluctuates with that of 



the environment. 



Pollutant A term referring to a wide range of toxic chemicals and 

 organic materials introduced into waterways from industrial plants and 

 sewage wastes. 



Pollution The addition of any substance not normally found in or 

 occurring in a material or ecosystem. 



Population A coexisting and interbreeding group of individuals of the 

 same species in a particular locality. 



Population Density The number of individuals of one population in a 

 given area or volume. 



Portal of Entry The pathway by which pathogens or parasites enter the 

 host. 



