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Paedophore: A type of fish that specializes in robbing the eggs or larvae from mouthbrooding cichlids. They accomplish this by sucking them out from the mother's mouth.

Paedophage: See Paedophore.

Palp: A segmented process of the mouthparts.

Papillae: A soft projection.

Parapatric Speciation: The differentiation into distinct species of populations experiencing some gene flow.

Parasite: An organism living on or in, and negatively affecting, another organism.

Parasitism: A type of symbiotic relationship in which one species (parasite) benefits from the relationship at the expense of the other (host), causing it harm and maybe even death.

Parr: A baby salmon with large dark spots on their sides for camouflage. Salmon parr usually live in freshwater for 1 to 2 years.

Particulate Organic Matter: Particulate material in the sea derived from the decomposition of the non-mineral constituents of living organisms.

Partner Ecosystems: Ecosystems that work together to maintain the diversity, productivity and ecological balance of other, nearby or connected ecosystems, or of the broader ecosystem of which they are a part.

Part-Per-Million (ppm): A measure of concentration of a dissolved material in terms of a mass ratio (milligrams per kilogram, mg/kg). One part of a contaminant is present for each million parts of water. For water analysis, parts per million often is presented as a mass per unit volume (milligrams per liter, mg/l). There are one million milligrams of water in one liter.

Patchiness: A condition in which organisms occur in aggregations.

Pathogens: Disease-causing organisms.

Peacock: An informal name given by hobbyists to the beautifully colored Cichlid genus Aulonocara, whose members are indigenous to Lake Malawi, Africa.

Peat: This form of dried moss can be used as a filter material to soften water and make it more acidic.

Pectoral fins: Paired fins, one on each side of the body located behind the gill covers. They are generally smaller, transparent, and very delicate.

Pelagic: Refers to living in the water of the ocean above the bottom. Pelagic organisms have the ability to swim around or move in some fashion. "Pelagic" is also used to refer (usually) to eggs that are basically at the mercy of the ocean currents. Benthos and benthic refers to living on or under substrate at the bottom of the ocean. Sessile means the organism is attached to the substrate. Pelagic is also a term that refers to the primary division of the sea, which includes the whole mass of water subdivided into neritic and oceanic zones; also pertaining to the open sea.

Pellets: Compacted aggregations of particles resulting either from egestion (fecal pellets) or from burrow-constructing activities of marine organisms.

Pelvic Fins: Fins which are located in front of the anal fin, just under the head.

Penetration Anchor: In hydraulically burrowing organisms, any device used to penetrate and gain an initial purchase on the sediment so that the body can be thrust in farther.

Peptides: Chains of amino acids; often portions of a protein molecule.

Perched Water Tables: These occur when a low permeability material, located above the water table, blocks or intercepts the downward flow of water from the land surface. Water mounds up above the impermeable material, creating another saturated zone with a water table.

Peripheral: Towards the edge or boundary of the shell.

Periphyton Collectors: Vegetarian fish that are highly specialized feeders. These fish comb algae from plants without eating or harming them.

Peristaltic Pump: A dosing pump which works by using rollers to squeeze flexible tubing.

Permeability: The property of porous materials indicating the ease with which liquids or gases will be transmitted through a soil or other porous material. Permeabilities are not affected by changing the type of liquid.

Petiole: The stalk of a leaf.

Pfiesteria: A toxic microorganism capable of killing fish and subsequently feeding off their flesh. Usually found in brackish waters. Pfiesteria has been associated with waters polluted with excessive nitrogen and phosphorus, but current scientific evidence is inconclusive and ongoing.

pH: A numerical measure of the acidity or alkalinity of water. The pH scale ranges from 1 (acidic) to 14 (alkaline). A pH of 7 is neutral. The technical definition of pH is that it is a measure of the activity of the hydrogen ion (H+) and is reported as the reciprocal of the logarithm of the hydrogen ion activity (-log10 [H+]). Therefore, a water with a pH of 7 has 10-7 moles per liter of hydrogen ions; whereas, a pH of 6 is 10-6 moles per liter. The pH scale ranges from 0 to 14. Most freshwater fish prefer a neutral pH, or a pH between 6.5 and 7.5. African Cichlids and livebearers, however, generally prefer a a slightly alkaline environment (7.8-8.8). Marine fish generally prefer a pH between 8.1 and 8.3.

Pharyngeal Teeth: Sometimes known as false-teeth or characin teeth. They are teeth that lie in the throat of some characins. These teeth act as a second set of teeth, in addition to the outer teeth. They are used for grinding the food before it is swallowed.

Pharynx: Throat.

Phenotypic Plasticity: The capacity of an individual to produce different phenotypes under different conditions. Non-genetic potential variability within the range of a single individual.

Phi Scale: Scale used for measuring the grain size of sediments. = -log2 (grain diameter).

Phosphate (PO4): There is no MCL for phosphate. In surface waters, phosphate is typically a limiting plant nutrient. The recommend maximum concentration in rivers and streams is a concentration of 0.1 mg/L of total phosphate. See also Phosphorous.

Phosphorous: An important trace element in the marine tank. Phosphorous is an essential element in the formation of new DNA (deoxyribonucleic acid) and it forms the high-energy bonds of ATP (adenosine triphosphate), which is the energy-currency of all life. When introduced into the aquarium through organic or inorganic means it promotes excessive algae growth. Phosphorous can be removed through water changes. See also Phosphate.

Photic Zone: The depth zone in the ocean extending from the surface to that depth permitting photosynthesis; usually less than 100m.

Photoperiod: Refers to the number of consecutive hours that light occurs in a day. In the aquarium, it is the number of hours that the lights are kept on.

Photophore: Luminous organ found in fish.

Photorespiration: Enhanced respiration of plants in the light relative to dark respiration.

Photosynthate: A substance synthesized in the process of photosynthesis.

Photosynthesis: The process by which plants manufacture ATP (adenosine triphosphate) and release oxygen from water, nutrients and carbon dioxide using energy absorbed from sunlight. Plants rely upon the green pigment chlorophyll to accomplish this.

Photosynthetic: The process by which organisms, usually plants, use the energy contained in light, usually sunlight.

Photosynthetic Quotient: In photosynthesis, the moles of oxygen produced, divided by the moles of carbon dioxide assimilated.

Photosynthetic Rate: The rate of conversion of dissolved carbon dioxide and bicarbonate ion to photosynthetic product.

Phototactic: Moving in response to light.

Physiological Incompatibility: The existence of some chemical or physical factor in the reproductive organs of a plant that prevents fertilization.

Physiological Race: A geographically defined population of a species that is physiologically distinct from other populations.

Phytoplankton: Small aquatic plants that drift in the sunlit surface of the ocean; commonly known as algae, these plants exist as producers at the bottom of many food chains. Phytoplankton form a symbiotic relationship with plankton.

Piebald: Refers to an animal's (fish) morphology, which is spotted or patched, especially with black and white.

Pink: A species of salmon with very large spots on their backs with large, oval black blotches on both lobes of their tails. Their scales are very small. The spawning adults take on a dull gray coloration on the back and upper sides with a creamy-white color below. The males develop a pronounced hump on their backs and are sometimes called "humpbacks."

Pinna: A part of a leaf of a fern, corresponding to a leaflet in some flowering plants.

Pinnate: Feather like. The "pinnules" which are found on many octocorals are small side branches of the polyp tentacle, which give it a "pinnate" appearance.

Pinniped: Member of the marine mammal group, characterized by four swimming flippers; for example seals and sea lions.

Pl*co: Another name for Pleco, or Plecostomus. A superstition on the internet where if you spell "Pleco" correctly, your pleco will soon die. That is why this word "Pl*co" was created.

Planktivorous: Feeding on planktonic organisms.

Plankton: The most minute and primitive creatures of the food chain. They are tiny organisms that drift through the layers of the ocean and serve as food for many small aquatic species. Plankton are the drifters of the sea. Although they may have some form of locomotion, water currents mostly carry them. Plankton is divided into macroplankton (jellyfish, sargassum weed) and microplankton. The microplankton is divided into zooplankton, tiny marine animals, and phytoplankton, or plants. Most fish start their lives as small animals in the plankton.

Planktotrophic Larva: Planktonic-dispersing larva that derives its nourishment by feeding in the plankton.

Planula: The planktonic larval form produced by scleractinian corals and coelenterates.

Plate: Major section of the earth's crust, bounded by such features as mid-ocean ridges.

Platyhelminthes: A phylum of animal that includes all flatworms.

Pleistocene: Period of time, going back to approximately 2 million years before the present, in which alternating periods of glaciation and deglaciation have dominated the earth's climate.

Pleuston: Refers to plankton that have a float protruding above the sea surface, such as the Portugese man-of-war.

Poikilotherm: An organism whose body temperature is identical to that of the external environment.

Poikilothermic: Cold-blooded; internal body temperature tends to vary with the external environment (as in fishes, amphibians and reptiles). Interestingly, in fast-swimming fishes such as tuna, core body temperatures may become elevated to accomodate faster movement; this is facilitated by specialized circulatory mechanisms such as rete mirablia. In contrast, mammals and birds are homeothermic, where the body's internal temperature is regulated. This is accomplished by the hypothalamus, which acts as a thermostat.

Point Source (PS) Pollution: The source of surface or groundwater pollution that originates from a well-defined source. Examples include: industrial effluent; large animal containment facilities; city wastewater treatment discharges; or chemical spills. Point sources commonly are associated with pipeline discharges of some type.

Point-Of-Entry (POE) Treatment: The treatment of all water entering a house, farmstead or other facility, regardless of its intended use. Anion exchange is an example of POE treatment to remove nitrates.

Point-Of-Use (POU) Treatment: The treatment of water at the point it is used. A common example would be water treatment at the kitchen sink for drinking and cooking uses. Reverse osmosis, distillation and ozone are examples of POU treatment methods.

Poison Fishing: A method of fishing which uses a chemical or plant substance that is sprayed into the water in order to kill or stun fish or marine life.

Pollutant: Any unwanted chemical or change in physical property that renders a water supply unfit for its intended use.

Pollution: The dirtying or befouling of any thing or place.

Polychaetes: Marine segmented worms, some in tubes, some free-swimming.

Polyculture: Cultivation of more than one species of organism in an aquaculture system.

Polyp: A polyp is the living unit of a coral. It also refers to the sessile stage in the life history of certain members of the phylum Coelenterata (Cnidaria).

Polyphyletic: Refers to a group of species that do not have one common ancestor species.

Population Density: Number of individuals per unit area or volume.

Porifera: The phylum comprising the sponges.

Porosity: The ratio of the volume of open spaces or voids to the total volume of a porous material. For example, a sand and gravel deposit may have 20 percent porosity. Porosity determines the amount of water that can be stored in a saturated formation. A saturated formation 100 feet thick with a porosity of 20 percent could store an equivalent water depth of approximately 20 feet.

Posterior: In the direction away from the head; opposite of anterior.

Potable Water Supply: A source of water that can be used for human consumption.

Power Filter: A generic term used to describe any type of filtration that is powered by an electric pump. They can either hang on the side of a tank or be submerged in it, and contain an internal pump to draw water through it. They provide mechanical filtration, and optionally chemical or biological filtration.

Power Head: A small submersible pump with only one moving part called the impeller. They are useful to create current within a tank (via a wavemaker) or to drive filters such as under gravel filters, canisters and protein skimmers.

ppm: Abbreviation for parts per million. See Parts-Per-Million.

Precipitation: The process where water vapor condenses in the atmosphere to form water droplets that fall to the earth as rain, sleet, snow or hail. Nebraska's long-term annual precipitation varies from 16 inches in the west to 34 inches in the southeast. Annual deviations can be greater than 30 percent.

Predaceous: Living by seizing or taking prey; predatory. See Predation.

Predation: The consumption of one organism by another.

Predator: An animal that hunts for food, or otherwise eats another animal.

Prefilter: This is a small mechanical filter attached to the input to another filter, usually biological. It is placed there to make sure that the biofilter does not get clogged with gunk, decreasing its effectiveness. In this manner it acts to remove large particles from the water, such as leaves, uneaten food, fish waster, etc.

Prey: An animal that is hunted or consumed as food by another animal.

Primary Producer: An organism capable of using the energy derived from light or a chemical substance in order to manufacture energy-rich organic compounds.

Primary Production: The production of living matter by photosynthesizing organisms or by chemosynthesizing organisms. Usually expressed as grams of carbon per square meter per year.

Proboscis: Tubular process of the head used in feeding.

Process: An elongation of the surface or an appendage; any prominent part of the body not otherwise definable.

Producer: A plant that manufactures plant material from water and carbon dioxide using energy from sunlight and nutrients in a process known as photosynthesis.

Productivity: The degree to which an ecosystem makes or yields a volume of plant, animal or thing. Also describes the amount of organic material synthesized by organisms in unit time in a unit volume of water.

Proleg: Any process or appendage that is used in support, locomotion or attachment; the fleshy unjointed thoracic or abdominal appendages of tricopterans, lepidopterans and dipterans; may be scleritized.

Prop Roots: Roots of mangrove trees that are extended out of the muddy soils and submerged in sea water at high tide, but are exposed at low tide; assist in slowing wave action and protecting soft mangrove soils against erosion.

Protein: A large food group that is essential for the proper development and maintenance of most of the living parts of plants and animals; proteins are necessary for life and are supplied by meat, fish, eggs, milk and other foods.

Protein Polymorphism: Presence of several variants of a protein of a given type (e.g., a certain enzyme, such as carboxylase) in a population.

Protein Skimmer: This chemical filter, also called a foam fractionator, removes organic impurities from the water by sending water through a fractionating column where many tiny air bubbles are pushed through it. The air bubbles generate "foam," which actually consists of organic impurities. The "foam" is channeled out of the device and is kept in a collection cup until it can be discarded. Protein skimmers come in three varieties, venturi, counter-current, and co-current. They are only effective in salt water. They may be placed in the tank, hung on the side, or placed in a sump.

Protozoa: A Kingdom that includes only single-celled organisms like amoeba, stentor, vorticella, and colonial ciliates.

Province: A geographically defined area with a characteristic set of species or characteristic percentage representation by given species.

Proximal: Away from the tip of a structure; opposite of distal.

Pseudofeces: Material rejected by suspension feeders or deposit feeders as potential food before entering the gut.

Pteropod: Pelagic snail whose foot is modified for swimming.

Pteropods: Group of holoplanktonic gastropods.

Pumping Water Level: The water level in a well when the pump is operating and water is being removed.

Pupa: Developmental stage in insects at the end of the larval period that is dormant and usually passed in a protected location, such as a cocoon or underground.

Pycnocline: Depth zone within which sea-water density changes maximally.
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