It refers to the time of day in which a fish is active. Fishes can be day active or night active, and this influences their behaviour.


Aestivation is a state of dormancy similar to hibernation, characterized by inactivity and a lowered metabolic rate.

/əˈɡrɛʃ(ə)n/ /ɡreɪd/

It refers to the fact that some fishes can have a territorial and aggressive behaviour, that can be caused by stress factors in the environment, for example, territory, sex specific selection and genetic variation. There is no fish species who display invasive behaviour, in specificity, because every species can be aggressive sometimes depending on the surroundings.

In a community tank, aggressions are more likely to occur, as this type of aquarium is less respectful of the biologic needs of the species. The biotope aquarium, on the other hand, gives to each species its niche, as it can be divided in different sections, suited to each inhabitant. To lessen the risk of aggressive behaviours, the number of organisms should be proportional to the aquarium volume.

  • Peaceful: species that are overall peaceful, but can have aggressive behaviours, especially during breeding, courtship or parental care
  • Aggressive/ territorial: species that are likely to show aggressive behaviours towards specimen of the same or of another species
  • Predator: species that are predator by nature


Agriculture is the process of producing food, feed, fiber, and many other desired products by the cultivation of certain plants and the raising of domesticated animals (livestock).

Agriculture, which accounts for 70 percent of water abstractions worldwide, plays a major role in water pollution. Farms discharge large quantities of agrochemicals, organic matter, drug residues, sediments, and saline drainage into water bodies. The resultant water pollution poses demonstrated risks to aquatic ecosystems, human health and productive activities (UNEP, 2016). So, directly or indirectly agriculture can have a direct impact on the water bodies it surrounds and on the existence of life forms that are found in the surrounding water.



Air temperature is a measure of how hot or cold the air is. It is the most commonly measured weather parameter. Air temperature affects the growth and reproduction of plants and animals, with warmer temperatures promoting biological growth. Air temperature also affects nearly all the other weather parameters. For instance, air temperature affects the rate of evaporation; relative humidity; wind speed and direction; precipitation patterns and types, such as whether it will rain, snow, or sleet.

Air temperature has a direct effect on the water temperature and is an interaction of natural environmental processes (e.g. air temperature, solar radiation, conduction from soil, etc.) and anthropogenic disturbances of the natural thermal regime, such as deforestation and hydroelectric development (Gras, 1969; Beschta et al.,1987; Benyahya et al., 2008). In recent years, a number of studies have identified global warming as another major influence of water temperature (Sinokrot et al., 1995; Webb, 1996; Mohseni et al., 1998, 1999; Pedersen and Sand-Jensen, 2007).

So, air temperature has a direct impact on water temperature that, in turn, affects dissolved oxygen, conductivity, oxidation reduction potential, pH, density, freshwater and saltwater temperature points, thermal stratification, pressure and water temperature points which govern the ice formation over water, and many other parameters, including compound toxicity (Source: So, all these factors influence the aquatic life.


Alluvium – a deposit of clay, silt, sand, and gravel left by flowing streams in a river valley or delta, typically producing fertile soil.


A cold-blooded vertebrate animal of a class that comprises frogs, toads, newts, salamanders, and caecilians. They need water, or a moist environment, to survive and they are able to absorb water through their very thin skin. Some of them are toxic amphibians and are very brightly colored. Most amphibians’ larvae are aquatic and free-swimming—frogs and toads at this stage are called tadpoles. After a certain stage in their development, they develop limbs and lungs and some may eventually lose their tails. As adults, they will come out of the water and spend the rest of their lives on land.

Many of the frog species are in danger of extinction as they need certain environmental conditions to survive. Too much sun, dry wind and lack of humidity can damage their skin and dehydrate the animal.


Relating to, living in, or suited for both land and water. Something that can survive both in land and water.


Fish (such as the salmon) migrating up rivers from the sea to spawn.


An amphidromous fish is a type of diadromous fish which migrates between fresh and saltwater. Unlike anadromous and catadromous fish, which migrate explicitly for the purposes of breeding, amphidromous fish migrate for other purposes. A typical cycle of amphidromy includes eggs hatching in freshwater or estuaries, larvae drifting out into the open ocean to feed and grow, juveniles returning to freshwater to feed and grow, and adults reproducing in freshwater. Gobies, such as those found on volcanic islands in the Pacific, exhibit an amphidromous life cycle.


Plants which germinate, flower and seed in one season or year, eg. button grass, fairy grass.

/əˈkweəriəm/ /ˌdekəˈreɪʃ(ə)n/

Fish tank ornaments and decorations that can be added to your aquarium, like driftwood, leaves, stones, snails, caves for the underwater natural appeal and to create a place for fish to hide and play.


Size of the aquarium, length, width and height, or often height and diameter. These are either in inches or cm. They are used to calculate the volume of the aquarium. The volume of water that the aquarium can hold will be always less or equal to the volume of the aquarium. See aquarium volume for more information.


Equipment used in an aquarium, like air pumps and accessories, chillers, cleaning equipment, CO2 equipment, dosing pumps filter cartridges & material, aquarium heaters , lighting, media reactors, overflow boxes, planting tools, protein skimmers, pumps, reef scaping equipment, reverse osmosis, testing kits & equipment, UV sterilizers, wave makers and many more.


The Volume of the Aquarium, the amount of space that the Aquarium occupies, or that is enclosed within it. Most of the Aquariums are rectangular, many square and a few cylindrical, but you may still get an odd-shaped aquarium. The volume of an aquarium can be calculated based on its shape. The volume of aquarium water also determines the number of fishes of a particular size that can be kept in the aquarium.

Rectangular Aquariums

  • Length  (inches) or  (cm) x Width  –  (inches) or (cm) Height – (inches) or (cm)
  • If in cm or any metric system, convert volume to Litres
  • If in Inches or any imperial (UK) convert volume to Gallons


  • The cube-shaped aquarium has the easiest volume equation – simply raise the edge length to the power of three: cube = length³ (in inches or cm)

Cylindrical Aquariums 

  • cylinder = π * (diameter / 2)² * height (in inches or cm)
  • π = pi is approximately 3.14
  • If your fish tank is a half-cylinder divide the formula above by 2


Quick Conversions:

  • 1 inch = 2.54cm
  • 1 cubic cm = 0.001 litres
  • 1 Cubic Inch = 0.004329 US Gallon
  • 1 Cubic Inch = 0.00360465 UK Imperial Gallon
  • 1 US Gallon = 3.78541 litres
  • 1 UK Imperial Gallon = 4.54609 litres
  • Temp = (32°F − 32) × 5/9 = 0°C
  • (F= Fahrenheit) (C=Celsius)


Aquatic biology is a sub-discipline of biology (the science of living things) concerned with the freshwater ecosystems of our planet: wetlands, rivers, lakes and ponds and river mouths.

Aquatic biologist study the ecology and behavior of plants, animals, and microbes living in the water by conducting field research, collecting samples, making observations of plant and animal organism health or behavior, analyzing data, and writing reports on their findings.


An aquatic biotope is described as an environment or a natural area where a set of specific collections of living beings, including that of plants and animals, coexist.

Ernst Haeckel (1834-1919), a German zoologist, first described the concept of biotope where he described how one ecosystem, its biota or living beings are shaped by environmental factors (such as water, soil, and geographical features) and by the relationships that each of these living beings have.


Aquatic plants are plants that live and survive in aquatic environments either freshwater, brackish or saltwater. They can be classified as hydrophytes or macrophytes. Hydrophytic plants grow in water or in soil that is consistently wet. Examples of hydrophyte habitats include fresh or salt water marshes, savannahs, bays, swamps, ponds, lakes, bogs, fens, quiet streams, tidal flats and estuaries.

A macrophyte is an aquatic plant that grows on the shore line, on the banks or in the water and is either emergent, submergent, or floating. Macrophytes need specific substrates to grow and provide unique habitats for other organisms. Macrophytes thrive in areas where there is a mixture of sand and muck, which is a semifluid, fine-grained, organic-rich sediment. They are also found in conditions that are optimal for upwelling along the coast when winds blow along the shore.

Macrophytes can modify the microclimate within the littoral zone by reducing the effects of waves and the creation of thermal gradients that prevent water from mixing. This, in turn, has effects on the nutrient availability and on the diffusion of oxygen through the sediment, and it also contributes to the nutrient cycling in the littoral zone. This creates a very positive environment for aquatic animals from the point of view of their growth, development and natural sustainability.

/ ärˈtēmēə/

Artemia salina, brine shrimp.Among the live diets used in the larviculture of fish and shellfish, nauplii of the brine shrimp Artemia constitute the most widely used food item. Annually, over 2000 metric tons of dry Artemia cysts are marketed worldwide for on-site hatching into 0.4 mm nauplii. Indeed, the unique property of the small branchiopod crustacean Artemia to form dormant embryos, so-called ‘cysts’, may account to a great extent to the designation of a convenient, suitable, or excellent larval food source that it has been credited with. Those cysts are available year-round in large quantities along the shorelines of hypersaline lakes, coastal lagoons and solar saltworks scattered over the five continents.

After harvesting and processing, cysts are made available in cans as storable ‘on demand’ live feed. Upon some 24-h incubation in seawater, these cysts release free-swimming nauplii that can directly be fed as a nutritious live food source to the larvae of a variety of marine as well as freshwater organisms, which makes them the most convenient, least labour-intensive live food available for aquaculture.

Although Artemia has been known to man for centuries, its use as a food for the culture of larval organisms apparently began only in the 1930’s, when several investigators found that it made an excellent food for newly-hatched fish larvae. During the 1940’s, most commercially available brine shrimp cysts represented collections from natural saline lakes and coastal saltworks. With the growing interest for tropical hobby fish in the late 1940’s, commercial value was attached to brine shrimp, thereby establishing a new industry.

Artemia nauplii or Brine shrimps are a fantastic livefood, they are used often on conditioning fish for spawning and also obviously very popular for usage in the aquarium. Brine shrimps are great at enhancing the colours of the fishes, where often reds and oranges along with blacks all colour up more vividly.

In its natural environment at certain moments of the year Artemia produces cysts that float at the water surface and that are thrown ashore by wind and waves. These cysts are metabolically inactive and do not further develop as long as they are kept dry. Upon immersion in seawater, the biconcave-shaped cysts hydrate, become spherical, and within the shell the embryo resumes its interrupted metabolism. After about 20h the outer membrane of the cyst bursts and the embryo appears, surrounded by the hatching membrane. While the embryo hangs underneath the empty shell the development of the nauplius is completed and within a short period of time the hatching membrane is ruptured and the free-swimming nauplius is born.

The first larval stage has a brownish-orange colour, a red nauplius eye in the head region and three pairs of appendages: i.e. the first antennae (sensorial function), the second antennae (locomotory + filter-feeding function) and the mandibles (food uptake function). The ventral side is covered by a large labrum (food uptake: transfer of particles from the filtering setae into the mouth). The instar I larva does not take up food as its digestive system is not functional yet; it thrives completely on its yolk reserves.

After about 8 h the animal molts into the 2nd larval stage. Small food particles (e.g. algal cells, bacteria, detritus) ranging in size from 1 to 50µm are filtered out by the 2nd antennae and ingested into the functional digestive tract.

The larva grows and differentiates through about 15 molts. Paired lobular appendages are appearing in the trunk region and differentiate into thoracopods. On both sides of the nauplius lateral complex eyes are developing. From the 10th instar stage on, important morphological as well as functional changes are taking place: i.e. the antennae have lost their locomotory function and undergo sexual differentiation. In males they develop into hooked graspers, while the female antennae degenerate into sensorial appendages . The thoracopods are now differentiated into three functional parts , namely the telopodites and endopodites (locomotory and filter-feeding), and the membranous exopodites (gills).

Adult Artemia (± 1 cm in length) have an elongated body with two stalked complex eyes, a linear digestive tract, sensorial antennulae and 11 pairs of functional thoracopods. The male has a paired penis in the posterior part of the trunk region. Female Artemia can easily be recognized by the brood pouch or uterus situated just behind the 11th pair of thoracopods. Eggs develop in two tubular ovaries in the abdomen. Once ripe they become spherical and migrate via two oviducts into the unpaired uterus.

Fertilized eggs normally develop into free-swimming nauplii (= ovoviviparous reproduction) which are released by the mother. In extreme conditions (e.g. high salinity, low oxygen levels) the embryos only develop up to the gastrula stage. At this moment they get surrounded by a thick shell (secreted by the brown shell glands located in the uterus), enter a state of metabolic standstill or dormancy (diapause) and are then released by the female (= oviparous reproduction). In principle both oviparity and ovoviviparity are found in all Artemia strains, and females can switch in-between two reproduction cycles from one mode of reproduction to the other. The cysts usually float in the high salinity waters and are blown ashore where they accumulate and dry. As a result of this dehydration process the diapause mechanism is generally inactivated; cysts are now in a state of quiescence and can resume their further embryonic development when hydrated in optimal hatching conditions.

Under optimal conditions brine shrimp can live for several months, grow from nauplius to adult in only 8 days time and reproduce at a rate of up to 300 nauplii or cysts every 4 days.

Artemia populations are found in about 500 natural salt lakes and man-made salterns scattered throughout the tropical, subtropical and temperate climatic zones, along coastlines as well as inland. This list still remains provisional as more extensive survey work should lead to the discovery of many more Artemia biotopes in different parts of the world. The distribution of Artemia is discontinuous: not all highly saline biotopes are populated with Artemia. Although brine shrimp thrive very well in natural seawater, they cannot migrate from one saline biotope to another via the seas, as they depend on their physiological adaptations to high salinity to avoid predation and competition with other filter feeders. Its physiological adaptations to high salinity provide a very efficient ecological defense against predation, as brine shrimp possess:

  • a very efficient osmoregulatory system;
  • the capacity to synthesize very efficient respiratory pigments to cope with the low O2 levels at high salinities;
  • the ability to produce dormant cysts when environmental conditions endanger the survival of the species.

Artemia therefore, is only found at salinities where its predators cannot survive (³ 70 g.l-1). As a result of extreme physiological stress and water toxicity Artemia dies off at salinities close to NaCl saturation, i.e. 250 g.l-1 and higher.

/ əˈkwatɪk/ /ˌvɛdʒᵻˈteɪʃn/

Consists of any kind of vegetation that lives near to or in the water. It includes aquatic grasses, mosses, algae, and aquatic plants. They provide important ecologic functions essential for the aquatic habitats, their water quality, and their fauna.


The tiny animals and plants that encrust hard substrates, such as rocks, in aquatic environments. “Aufwuchs” in German refers to “surface growth” or “overgrowth” of parts of rooted plants, both of marine and freshwater environments, for example algae –especially green algae and diatoms – make up the dominant component of aufwuchs communities. Many tiny small crustaceans, protozoans’ rotifers, larvae are part of the freshwater aufwuchs faunas. Aufwuchs are source of food for many fishes, like hill stream loaches, gobies, cichlids etc. and they have adopted to use Aufwuchs as a natural food source.


The Biotope Aquarium Contest is a competition organized by the Biotope Aquarium Project that can be entered by any aquarium enthusiast, following the directories available on the site. The competitions have been taking place since 2016, both online and with a final contest live, where aquarists are able to show their skills and biotope correct aquariums.

Check out guidelines and instruction to submit and participate.

BIOTOPE AQUARIUM Model is an authentic re-construction of the original – often of a very small – aquatic biotope, which might disappear at any time without warning, or has already vanished. This little piece of Nature benefits the well-being of the aquarium inhabitants if:

  • simulates BIOTOPE In NATURE
  • replicates conditions of lake, creek or river
  • has correct water type and chemical parameters
  • provides a living space for the correct biological community
  • applies the correct décor material

BAP Map or BIOTOPE AQUARIUM Project Map is the main instrument of the biotope mapping offered to beginners and experienced aquarists to build their own BIOTOPE AQUARIUM Model. Geographic map marks the GPS locations with the detailed aquatic biotope research and data on aquatic inhabitants that includes:


The term benthic refers to anything associated with or occurring on the bottom of a body of water. The animals and plants that live on or in the bottom are known as the benthos. In ocean waters, nearshore and estuary areas are most frequently mapped.

Benthic fish, sometimes called groundfish, are denser than water, so they can rest on the sea floor. They either lie-and-wait as ambush predators, maybe covering themselves with sand or otherwise camouflaging themselves, or move actively over the bottom in search for food – benthos and zooplankton.


It is benthopelagic a species that lives and feeds near or at the bottom of a watercourse, as well as in midwaters or near the surface. These species feed on benthic as well as free swimming organisms.


1 Australia. a : a blind channel leading out from a river. b : a usually dry streambed that is filled seasonally.

2 Australia : a backwater forming a stagnant pool.

The term billabong comes from the Wiradjuri word ‘bilabang’ which translates to ‘lake’. The Wiradjuri language is from the Aboriginal Wiradhuric tribe, located in New South Wales. The section bila translates to ‘river’, whereas the bang refers to ‘continuing in time or space’.


The section dedicated to the presentation of biotopes in the environment. Each page introduces a biotope in nature, giving information about the location, the inhabitants, the aquatic vegetation, the water chemistry, the substrate, the aquatic biotope and the environment. Each page is completed with photos and videos.


Biocoenosis refers to the indeendent organisms that live together in a specific habitat, biotope, or ecosystem interacting with one another and forming an ecological, closely integrated community. An ecological community can also be called a biocoenosis.


Also called biological diversity, it indicates the variety of extant species in the environment and also encompasses the genetic variability within the species that form biological communities.


A group of diverse species that occupy the same specific area and interact with each other. The overall structure of a community is determined by the diversity, the abundance and the specific interactions among the species within it.


From Greek bios (“life” or “organism”) and topos (“place”). A biotope is a limited area of uniform environmental conditions that provides living space for several organisms that coexist, interact, and cooperate, thus forming a biological community. Biotopes and the communities they host make up ecosystems that change constantly because of abiotic and biotic factors, but which are, nowadays, often threatened by human activity.


A biotope aquarium is an aquarium that replicates the natural biotope and ecosystem, where aquatic organisms, especially those threatened in the environment, can survive and adapt to a new home. For a biotope aquarium to be correct and replicating exactly the original habitat of the living species, organisms, environmental elements and conditions need to be selected accurately.


For fresh- and brackish water environments, biotope mapping allows a detailed description of the existing environment. A biotope is described as a habitat with its associated species assemblage and a detailed field survey allows the various biotopes present in an area to be identified and mapped.

A biotope is generally not considered to be a large-scale phenomenon. For example, a biotope might be a neighbouring park, a back garden, even potted plants or a fish tank on a porch. In other words, the biotope is not macroscopic but a microscopic approach to preserving the ecosystem and biological diversity.


Brackish water is a broad term used to describe water, whose salinity is between that of fresh and marine water, and these are often transitional areas where such waters mix.

An estuary, which is the part of a river that meets the sea, is the best-known example of brackish water. Estuaries are highly variable environments because the salinity can change drastically over a relatively short distance, ranging from 10% to 32%, and over time of day due to tidal cycles – for example, high tide bringing saltier marine waters farther up into the estuary.

Seasonal increases in freshwater due to rainfall or snowmelt will decrease the salinity at a given point in the estuary. In order to survive here, resident microbes must be adapted to these large fluctuations in salinity. Despite this challenge, estuaries are very productive environments.

Brackish waters occur naturally as brackish groundwater in subsurface saline aquifers, as surface water due to natural erosion, or groundwater in coastal aquifers. Natural brackish water, particularly brackish groundwater, exists in most continents in quantities almost equal to or more than fresh groundwater and surface waters combined. Human activities can also cause fresh surface water and groundwater resources to become brackish through consumptive use and increase in their salt loading.


Carnivorous fish have a meat-based diet which can include insects, other fish, and other invertebrates. They usually have different body structures, for example they can have a larger mouth, larger teeth and a more aerodynamic body for quickly swimming through the water. Some carnivorous fish are active hunters that will chase down their preys, like sharks; others wait for the prey to come to them, also in the deepest parts of the ocean. Some other species, like catfish or loach, resort to scavenging and catch all the food that has sunk to the bottom.

Common carnivorous aquarium fishes are some types of cichlid, arrowana, and piranhas. They should be regularly offered live food and frozen food, like feeder fish, brine shrimp, mosquito larvae, worms, mollusks, and other invertebrates.

CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora) is a global agreement among governments, adopted in 1975 in order to regulate or ban international trade in plant or animal species that are under threat and safeguard their survival.


ChironomusThe Chironomidae are a large family distributed worldwide, with more than 130 genera and 700 species in North America alone. They are often mistaken for adult mosquitoes but lack the long proboscis and are unable to feed on blood. Adults are short-lived, living only a few days to several weeks. Some imbibe honeydew and other natural sugars, but some take no food at all as adults.

Adult chironomid midges are 1–10 mm long, with slender legs, narrow, scaleless wings, and plumose antennae in the adult males.

Most chironomid larvae are aquatic or semiaquatic and construct tubes in, or attached to, the substrate. They are often the most abundant benthic organisms and occur in all types of habitats, including rivers, streams, lakes, ponds, water supplies, and sewage systems.

Chironomid larvae are cylindrical and have paired prolegs on the prothoracic and last abdominal segments. The head is heavily sclerotized and nonretractile. They have no spiracles. Many species, however, have a hemoglobin-like substance in their hemolymph and are called bloodworms because of their pink or red color. Most species are detritus feeders that graze on aquatic substrates. Others filter drifting food particles from the water with strands of saliva or are predators on other chironomid larvae or oligochaete worms.

They constitute a very high protein food, very welcome by all omnivorous and carnivorous fish, but obviously not suitable for vegetarian ones. Growing at home does not present many problems, as you can read below; the risk is that of introducing into the tank, together with the live food, other undesirable creatures, such as larvae of other insects, or parasites that can transmit to the fish.

Frozen bloodworms are a little safer from this point of view, although they are not entirely free from these risks, so they should be bought in reliable shops, where you can be relatively sure that the cold chain has not been interrupted. Frozen bloodworms must be rinsed thoroughly before giving it to the fish.

Chlorosis is a yellowing of normally green leaves due to a lack of chlorophyll. Many factors, singly or in combination, contribute to chlorosis. In northern Illinois, some of the most common causes among trees and shrubs include nutrient deficiencies related to soil alkalinity (high pH), drought, poor drainage, and compaction of the soil. Common tree species exhibiting chlorosis are pin oak, red maple, white oak, river birch, tulip tree, sweet gum, bald cypress, magnolia, and white pine.


The presence of sediments in the water can be measured: the ratio of the dry sediment in a mixture of water and sediments/ the total weight of the mixture.

Waters with a high concentration of sediments are usually turbid.


The capability of a fluid – in our case water – to conduct electricity and let an electrical flow pass through it. It is strictly linked to the concentration of ions, that result from various minerals and inorganic materials dissolved in the fluid. The more ions are present, the more conductive is the fluid.


The genus Daphnia includes more than 100 known species of freshwater plankton organisms found around the world. They inhabit most types of standing freshwater except for extreme habitats, such as hot springs. All age classes are good swimmers and are mostly pelagic, i.e., found in the open water. They live as filter feeders, but some species may frequently be seen clinging to substrates such as water plants or even browsing over the bottom sediments of shallow ponds. Adults range from less than 1 mm to 5 mm in size, with the smaller species typically found in ponds or lakes with fish predation. The ecology of the genus Daphnia may be better known than the ecology of any other group of organisms.

Daphnia are planktonic crustaceans that belong to the Phyllopoda (sometimes called Branchiopoda), which are characterized by flattened leaf-like legs used to produce a water current for the filtering apparatus. Within the branchiopods, Daphnia belong to the Cladocera, whose bodies are enclosed by an uncalcified shell, known as the carapace.

It has a double wall, between which hemolymph flows and which is part of the body cavity. The carapace is largely made of chitin, a polysaccharide. Cladocera have up to 10 pairs of appendages, which are (from front to back): antennules, antennae (the second antennae, used for swimming); maxillae; and mandibles; followed by 5 (as in Daphnia) or 6 limbs on the trunk. The limbs form an apparatus for feeding and respiration. At the end of the abdomen is a pair of claws. The body length of Cladocera ranges from less than 0.5 mm to more than 6 mm. Males are distinguished from females by their smaller size, larger antennules, modified post-abdomen, and first legs, which are armed with a hook used in clasping.

Daphnia are one of the finest and most universally accepted live foods for most fish. Many fish species can be kept in excellent physical condition by feeding live daphnia to them several times per week. Daphnia are extremely effective at bringing many fish into spawning condition. This is especially true for cyprinids. Daphnia can be cultured in just about any container that holds water and is non‐toxic.

|ˌdiːˌfɔːrɪˈsteɪʃn| Brit. |ˌdiːfɒrɪˈsteɪʃ(ə)n|

Deforestation or forest clearance is the removal of a forest or stand of trees from land that is then converted to non-forest use.

Deforestation impacts aquatic ecosystems in a number of ways. It increases soil erosion, which increases turbidity and sedimentation, and causes contaminants to enter streams. Deforestation also changes water temperature and light conditions, reduces levels of litter detritus and increases periphyton, reduces habitat complexity, affects hydrological processes, is associated with the increase of introduced species in streams, and affects alpha and beta diversity, community composition, and ecosystem function. Deforestation has even been associated with morphological changes in fish.

/dɪˈzɒlvd/ /ˈɒksᵻdʒ(ə)n/

It measures how much oxygen is found in the water. The presence of oxygen in the water is a positive indicator of quality, while its absence could be a sign of pollution. Sources of dissolved oxygen can be atmosphere, aeration and photosynthesis from algae and aquatic plants.


The tallest plant species present at a site.  There must be several individuals of the same plant present at one site for it to be the dominant species.

/ˈdreɪnɪdʒ/ /ˈbeɪs(ə)n/

Region or catchment area that includes all the minor, superficial watercourses that funnel and pour in the main river. The drainage basin acts as a collector of the precipitations which flow to a single or more streams, including the water of the main watercourse and its tributaries.


The study of relationships between living organisms and their environment.


An ecosystem is a biological system that consists of different organisms, interacting which each other, and their physical environment. Every biotic (living) and abiotic (non-living) component of the ecosystem contribute to make it function as a unit. Nature is made of different units; thus, of different ecosystems.

An ecosystem is based on an ecological community made of different populations of different organisms which live and work together in a particular environment or habitat.

El Niño and La Niña events are a natural part of the global climate system. They occur when the Pacific Ocean and the atmosphere above it change from their neutral (‘normal’) state for several seasons. El Niño events are associated with a warming of the central and eastern tropical Pacific, while La Niña events are the reverse, with a sustained cooling of these same areas.


Plant or animal native and restricted to a certain place.


An euryhaline organism is an animal that is able to live in fresh water, salt water, and all waters in between.

Like the Arabian pupfish, Aphanius dispar, is a euryhaline fish inhabiting both inland nearly-freshwater desert ponds and highly saline Red Sea coastal lagoons of the Arabian Peninsula. Desert ponds and coastal lagoons, located respectively upstream and at the mouths of dry riverbeds (“wadies”), have been found to potentially become connected during periods of intense rainfall, which could allow the fish to migrate between these different habitats. Flash floods would therefore flush Arabian pupfish out to sea, requiring a rapid acclimation to a greater than 40 ppt change in salinity.


(of a lake or other body of water) rich in nutrients and so supporting a dense plant population, the decomposition of which kills animal life by depriving it of oxygen.

Eutrophication is considered to be a serious environmental concern since it often results in the deterioration of water quality and the depletion of dissolved oxygen in water bodies. Eutrophic waters can eventually become “dead zones” that are incapable of supporting life.


Water hardness is caused by the presence of calcium and magnesium ions and it indicates the capacity to precipitate soaps, that deposits on the bottom of the solution. Water is, thus, categorized in hard, medium, or soft water. Groundwater tends to be harder, while surface water is generally softer.

General guidelines for classification of waters are:

  • Soft: 0-60 mg/L
  • Moderately hard: 61-120 mg/L
  • Hard: 121 to 180 mg/L
  • Very hard: more than 180 mg/L

In freshwater tanks, we test for GH because calcium and magnesium are similar in depletion (not the case in marine aquarium). The units of measure are parts per million (1 ppm = 1 mg/L) or degrees of hardness (dKH and dGH).


  • of animals/fishes: living in flocks or loosely organized communities; living in shoals/flocks/herds.
  • of plants: growing in open clusters or in pure associations.

The gregarious behavior, serves to provide benefits to fish in relation to obtaining food, reproduction, protect the group and reduce energy expenditure, however the avoidance of predators being by several authors as the most mentioned advantage, but this will not always be effective, as it is closely related to the predator’s ability to increase the rate of consumption on a polarized group of fish. The factors that cause the formation of certain type of group depend on several causes such as species type, age, biotic and abiotic factors, among other and the possible combinations between these.


The place in which an organism or a community or organisms live and grow, including all factors and conditions of the surrounding environment that the organisms need in order to survive. The main components of a habitat include space, shelter, water, and food in the correct amount for each species.


In central Amazonia the prevailing floodplain forest is differentiated into nutrient-rich white water “várzea” and nutrient-poor blackwater or clear water “igapó”.

The vast areas of igapó forests – seasonally flooded forests for extended periods (4-10 months) on blackwater (and clearwater) river/lake margins, – are the home to innumerous endemic species of plants and animals.

The black-water and clear-water rivers carry low loads of suspended matter and solutes, resulting in a scarcity of nutrients. These rivers have brown- or tea-colored waters, the color being the result of high concentrations of humic substances and organic acids suspended in the water.

Igapó forests mostly occur along black and clear water rivers that drain the Paleozoic and/or Precambrian shields of Guyana and Central Brazil. The floodplain of these rivers covers an area of approximately 200.000km2 from which the most part is covered by close canopy forest.

The largest clear water rivers are the Xingu, Tapajós and Trombetas whose floodplains cover approximately 67.000km2, while the main example of blackwater river is the Negro River, whose floodplains cover ∼118.000km2, supporting the largest black-water inundation forest in the world.

Blackwater igapó: the balckwater system, represented by the Rio Negro basin, originated on the Precambrian shield of the northern region of the Amazon basin. Its transparent red-brown color originates from a high content of dissolved humic and tannin substances, which is about 10 times higher than in the Solimões/Amazon River.

The water is poor in nutrients and electrolytes with dominance of sodium among the major cations, presenting low alcalinity. The pH and electrical conductivity values are less than 5.0 and 25 µS/cm-1, respectively. The black color and acidity of the water are due to the elevated concentrations of dissolved organic material such as humic and fulvic acids.

Clearwater igapó: the rivers of the clearwater type have their upper catchments in the Central Brazilian and Guiana Archaic/Precambrian shields and are charachterized by pH values that vary between 5.0 and 7.0 and electrical conductivity in the range of 10-53.6 µS/cm-1. The water transparency can reach up to 355cm or still higher; but transparency values less than 100cm are also common in these rivers.


Invasive Alien Species (IAS) are living organisms, including animals and plants, introduced accidentally or deliberately into a geographical area different from that of their origin, with serious negative consequences for the new environment. They represent a major threat to native plants and animals worldwide and cause damage worth billions of euros to the global economy every year.


An invertebrate is an animal that lacks a vertebral column and, thus, does not belong to the chordate subphylum Vertebrata. Generally, invertebrate animals are soft-bodied, lacking a rigid internal skeleton for the attachment of muscles. Some of them, however, possess a hard outer skeleton that protects the body.

Invertebrates make up more than the 90% of all living animal species, such as sea stars, sea urchins, earthworms, sponges, jellyfish, lobsters, crabs, insects, spiders, snails, clams, and squid.

IUCN (International Union for Conservation of Nature and Natural Resources) is an organization founded in 1948 whose aim is to influence, encourage, and assist societies to conserve the integrity and diversity of nature,and ensure that any use of natural resources is equitable and ecologically sustainable.

IUCN has drafted a Red List Categories and Criteria that is intended to be an easily and widely understood system for classifying species at high risk of global extinction. Species are divided into the followng categories:

  • Not Evaluated (N/E);
  • Data Deficient (DD): a taxon about which there is no adequate information to make an assessment about its endangerment;
  • Least Concern (LC): a taxon that does not qualify as endangered;
  • Near Threatened (NT): a taxon close to qualifying for a threatened category;
  • Vulnerable (VU): taxons considered to be facing high risk of extinction in the wild;
  • Endangered (EN): a taxon considered to be facing a very high risk of extinction in the wild;
  • Critically Endangered (CR): a taxon considered to be facing an extremely high risk of extinction in the wild;
  • Extinct in the Wild (EW): a taxon known to survive in cultuvation, captivity or as a neutralised population well outside the past range. A taxon is presumed EW when surveys in the wild have failed to record it;
  • Extinct (EX): a taxon which surveys have failed to record.


Carbonate hardness is the measure of the alkalinity of water, determined by the presence of carbonates of calcium. Carbonate hardness is related to the ability of water to maintain a stable environment and a stable pH.


With regard to the forms in the sections BAM, FISH, and PLANT, it refers to the level of complexity to decorate the biotope tank, find the species and décor material in the general aquarium shops and manage a species in a biotope correct aquarium. Ratings are: easy, medium or difficult.

/məˈriːn//fɪʃ/ /əˈkweəriəm/

Macrophytes are aquatic plants growing in or near water. They may be either emergent (i.e., with upright portions above the water surface), submerged or floating. Examples of macrophytes include cattails, hydrilla, water hyacinth and duckweed.

Macrophytes provide cover for fish and substrate for aquatic invertebrates. They also produce oxygen and provide food for some fish and other wildlife. Macrophytes respond to a wide variety of environmental conditions, are easily sampled, do not require laboratory analysis and are used for calculating simple abundance metrics.

The depth, density, diversity and types of macrophytes present in a system are indicators of waterbody health. Where submerged aquatic macrophytes are abundant, they can have a heavy influence on habitat structure, fishability, recreational use and nutrient dynamics. The absence of macrophytes may indicate water quality problem such as excessive turbidity, herbicides or salinization which interfere with plant growth and development. However, an overabundance of macrophytes can result from high nutrient levels and may affect ecosystem health, recreational activities and the aesthetic appeal of the system.

/məˈriːn//fɪʃ/ /əˈkweəriəm/

This is a salt water tank that houses colourful marine plants and animals in a contained environment. Marine aquaria are further subdivided by hobbyists into fish only, fish only with live rock, and reef aquaria.


Physical characteristics
At a given scale, a habitat encompasses a spatial domain, homogeneous in relation to environmental parameters. The environment’s physical and chemical characteristics are taken to encompass the substratum (rock or sediment) and the particular conditions, which are characteristic of the local environment. For the marine environment such conditions include wave exposure, salinity and tidal currents. Such conditions vary within a range, which is characteristic of the habitat. This means that a habitat is limited in space. The biotope integrates the environmental factors which structure the habitat. With regard to physical parameters, the biotope results from a balance between hydrodynamic parameters, physico-chemical parameters such as salinity and continental inputs (including pollutants and nutrients), the local geomorphology creating sheltered or exposed habitats, regional sedimentary characteristics and regional lithology conditioning the type of deposit or the type of substratum. The habitat is indicated by a limited set of words resuming the local conditions, i.e. muddy sand or rock platform. Such expressions integrate the various parameters which play a role in the habitat of a particular population.

Biological features
The term ‘habitat’ is more widely (and abusively) used to also include living organisms. Within space, species interact and constitute communities. From a biological point of view, the bio-facies or biotope results from a balance between the regional living environment and the local conditions. The presence of a species will be dependant on access to the ecosystem considered and to other biological requirements, i.e. the recruitment of young stages, trophic conditions.


Marine, or saltwater fish are all those fish species that live in the ocean, where they either live alone or form schools. Different marine fish species live in different marine habitats, that can largely vary in terms of salinity and alkalinity levels, temperature, and pH values.

Marine fish species are commonly kept in home aquaria and they are constantly threatened by the fish industry.


Collection and comparison of information to determine type, extent and cause of change.


In biology,

  • (of a species or population) showing little or no variation in morphology or phenotype.
  • (of an animal species) having sexes that are similar in size and appearance.


In biology, a genus or species with only one type of representative. A monotypic taxon is a taxonomic group that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or infraspecific taxa. In the case of genera, the term “unispecific” or “monospecific” is preferred.


(especially of a lake) relatively poor in plant nutrients and containing abundant oxygen in the deeper parts.

Oligotrophic environments are those that offer little to sustain life. These environments include deep oceanic sediments, caves, glacial and polar ice, deep subsurface soil, aquifers, ocean waters, and leached soils.


Omnivore fish species possess a versatile diet, consuming both plants and smaller aquatic animals. This adaptability allows them to thrive in various habitats, contributing to their diverse presence across the world’s waters.

An omnivore will eat a variety of meat and vegetable matter. Although omnivores can and will eat vegetable matter, they cannot digest some types of grains and plants. Their teeth and digestive tract possess some of the traits of both the carnivore and the herbivore.

Omnivores are the easiest of all fish to feed, as they eat flake foods as well as live foods, and everything in between. For that reason, omnivores are an excellent choice for a community tank.

It’s important to feed your fish the proper diet, as their bodies are designed for certain types of food.



In biology, the process of individual development from a single cell, an egg cell or a zygote, to an adult organism is known as ontogeny.


An ornamental fish is a fish that is kept in home aquarium for aesthetic purposes. There are a lot of different fish species that are considered ornamental and that can be included in home aquaria; they encompass a wide variety of species, of many shapes, sizes, and colours.


Oxisols (from French oxide, “oxide”) are very highly weathered soils that are found primarily in the intertropical regions of the world. These soils contain few weatherable minerals and are often rich in Fe and Al oxide minerals.

The main processes of soil formation of oxisols are weathering, humification and pedoturbation due to animals. These processes produce the characteristic soil profile. They are defined as soils containing at all depths no more than ten percent weatherable minerals, and low cation exchange capacity.


Paramecium or Paramoecium is a genus of unicellular ciliated protozoa characterised by the presence of thousands of cilia covering their body. Paramecium are found in freshwater, marine and brackish water. They are also found attached to the surface. Reproduction is primarily through asexual means (binary fission).

In the aquaristics Paramoecium and rotifers are known under the collective name Infusoria which stands for microscopic organisms that dwell in waterbodies, feeding on detrietus and smaller single celled organisms.


A plant whose life cycle extends for more than two years (e.g. Cyperus).  Some perennials, such as grasses and herbs, have above-ground parts, which die off in unfavorable seasons leaving an underground structure, such as a bulb or rhizome, to produce new growth when the season is favourable.


Perennial rivers have an uninterrupted flow of water throughout the year, regardless of the season, although some perennial rivers could stop flowing during severe drought. Perennial rivers drain a huge area forming the basin of the river, such as instance the Amazon River, which covers an area of 7.500.000 km² and is the largest basin in the world. The Congo River in Africa drains an area of 4.014.500 km2, making it the second largest river basin in the world.

Scale indicative of the acidity or basicity of a substance, that is influenced by minerals and dissolved materials. A substance is acid when its pH ranks between 0 and 5,5 and basic, or alkaline, when its pH is between 7,5 and 14. When the pH is between 5,5 and 7,5, a substance is considered neutral.


Derived from the Greek words phyto (plant) and plankton (made to wander or drift), phytoplankton are microscopic organisms that live in watery environments, both salty and fresh.

Some phytoplankton are bacteria, some are protists, and most are single-celled plants. Among the common kinds are cyanobacteria, silica-encased diatoms, dinoflagellates, green algae, and chalk-coated coccolithophores.

Like land plants, phytoplankton have chlorophyll to capture sunlight, and they use photosynthesis to turn it into chemical energy. They consume carbon dioxide, and release oxygen. All phytoplankton photosynthesize, but some get additional energy by consuming other organisms.

Phytoplankton growth depends on the availability of carbon dioxide, sunlight, and nutrients. Phytoplankton, like land plants, require nutrients such as nitrate, phosphate, silicate, and calcium at various levels depending on the species. Some phytoplankton can fix nitrogen and can grow in areas where nitrate concentrations are low. They also require trace amounts of iron which limits phytoplankton growth in large areas of the ocean because iron concentrations are very low. Other factors influence phytoplankton growth rates, including water temperature and salinity, water depth, wind, and what kinds of predators are grazing on them.


Phytoremediation is a bioremediation process that uses various types of plants to remove, transfer, stabilize, and/or destroy contaminants in the soil and groundwater.

Worldwide population is generating an enormous amount of waste discharged into waterways. Waste dominated one of them is domestic waste. Domestic waste is divided into two categories: first, domestic waste water from the washing water such as soaps, detergents, oils and pesticides; The second is the liquid waste from the latrines such as soap, shampoo, feces and urine. This wastewater as a potential environmental pollutant if not managed properly. The result of this waste water enters the body when water will affect the condition of the water body. The more densely populated, the more waste that must be controlled.

Heavy metal accumulation in soil has been rapidly increased due to various natural processes and anthropogenic (industrial) activities. As heavy metals are non-biodegradable, they persist in the environment, have potential to enter the food chain through crop plants, and eventually may accumulate in the human body through biomagnification. Owing to their toxic nature, heavy metal contamination has posed a serious threat to human health and the ecosystem. Therefore, remediation of land contamination is of paramount importance. Phytoremediation is an eco-friendly approach that could be a successful mitigation measure to revegetate heavy metal-polluted soil in a cost-effective way.

There are several different types of phytoremediation mechanisms. These are:

  1. Rhizosphere biodegradation. In this process, the plant releases natural substances through its roots, supplying nutrients to microorganisms in the soil. The microorganisms enhance biological degradation.
  2. Phyto-stabilization. In this process, chemical compounds produced by the plant immobilize contaminants, rather than degrade them.
  3. Phyto-accumulation (also called phyto-extraction). In this process, plant roots sorb the contaminants along with other nutrients and water. The contaminant mass is not destroyed but ends up in the plant shoots and leaves. This method is used primarily for wastes containing metals. At one demonstration site, water-soluble metals are taken up by plant species selected for their ability to take up large quantities of lead (Pb). The metals are stored in the plantÍs aerial shoots, which are harvested and either smelted for potential metal recycling/recovery or are disposed of as a hazardous waste. As a general rule, readily bioavailable metals for plant uptake include cadmium, nickel, zinc, arsenic, selenium, and copper. Moderately bioavailable metals are cobalt, manganese, and iron. Lead, chromium, and uranium are not very bioavailable. Lead can be made much more bioavailable by the addition of chelating agents to soils. Similarly, the availability of uranium and radio-cesium 137 can be enhanced using citric acid and ammonium nitrate, respectively.
  4. Hydroponic Systems for Treating Water Streams (Rhizofiltration). Rhizofiltration is similar to phyto-accumulation, but the plants used for cleanup are raised in greenhouses with their roots in water. This system can be used for ex-situ groundwater treatment. That is, groundwater is pumped to the surface to irrigate these plants. Typically hydroponic systems utilize an artificial soil medium, such as sand mixed with perlite or vermiculite. As the roots become saturated with contaminants, they are harvested and disposed of.
  5. Phyto-volatilization. In this process, plants take up water containing organic contaminants and release the contaminants into the air through their leaves.
  6. Phyto-degradation. In this process, plants actually metabolize and destroy contaminants within plant tissues.
  7. Hydraulic Control. In this process, trees indirectly remediate by controlling groundwater movement. Trees act as natural pumps when their roots reach down towards the water table and establish a dense root mass that takes up large quantities of water.


Plantlets are young or small plants that can grow or be produced on the margins of the plant itself as a form of asexual reproduction.


Plant litter refers to the dead plant material, such as leaves, bark, needles and twigs that have fallen on the ground or in the water. It makes up debris or organic material whose constituents add to the soil or water. It is an important factor for the dynamics of an ecosystem.


An organism (fish) that inhabits or prefers an environment of (especially rapidly) flowing water.

/rʌɪˈpɛːrɪən/ /zəʊn/

The area between land and a watercourse, characterized by the presence of many aquatic plants and other vegetation that can grow to create ana actual forest on the banks of a river. The riparian zone is important for the wellness and the protection of the aquatic environment.


A riverbed is the bed or the channel in which a river flows and that is shaped by the flowing water. A riverbed can be more or less wide, from a few feet to a thousand metres. Nevertheless, from time to time a riverbed might not contain flowing water or be dry all the same. This particularly happens in regions of the world where dry and rain season alternate. Furthermore, riverbeds can consists of different materials, such as rock, sand, clay, silt, or other unconsolidated materials resulting from earlier deposition.


Area of land around a river or another water body that is collected in that area because of the conformation of the landscape. All the water that is collected in the same catchment area eventually flows together in the same water body.


A rhizome is a horizontal underground plant stem, which is able to produce the shoot and root systems of a new plant. These stems allow a parent plant to produce offrispring through asexual reproduction, that is, propagation, and to survive in adverse condition. The rhizomes perform several functions that help the growth of the plant, such as storing food and save nutrients (proteins, carbohydrates, minerals).


Water that is saline contains significant amounts – referred to as “concentrations” – of dissolved salts, the most common being the salt we all know so well – sodium chloride (NaCl). In this case, the concentration is the amount (by weight) of salt in water, as expressed in “parts per million” (ppm). If water has a concentration of 10.000 ppm of dissolved salts, then one percent (10.000 divided by 1.000.000) of the weight of the water comes from dissolved salts.

Here are our parameters for saline water:

  • Fresh water – Less than 1.000 ppm
  • Slightly saline water – From 1.000 ppm to 3.000 ppm
  • Moderately saline water – From 3.000 ppm to 10.000 ppm
  • Highly saline water – From 10.000 ppm to 35.000 ppm
  • By the way, ocean water contains about 35.000 ppm of salt.

Small amounts of dissolved salts in natural waters are vital for the life of aquatic plants and animals; higher levels of salinity alter the way the water can be used, yet even the most hypersaline water can be used for some purposes. However, high levels of salinity and acidity (if present) are harmful to many plants and animals.


It refers to climates or regions which lack sufficient rainfall for regular crop production.  Usually defined as a climate with annual rainfall greater than 250 mm but less than 375 mm.


The detachment and transportation of soil and its deposition at another site by wind, water or gravitational effects.

Natural erosion: erosion occurring under natural environmental conditions, undisturbed by humans.

Accelerated erosion: erosion which is attributable to the influence of human activities.  See also scald, hummockingand pedestalling.

Water erosion: an erosion process in which soil is detached and transported from the land by the action of rainfall,  runoff and seepage.  Types of water erosion include:

  • Splash erosion: the spattering of soil particles caused by the impact of raindrops on the soil; an important component of sheet erosion.
  • Sheet erosion: the removal of a fairly uniform layer of soil from the land surface by wind and raindrop splash and /or runoff. No rills are formed.
  • Rill erosion: the removal of runoff from the land surface whereby numerous small channels are formed.  Rills are defined as small channels up to 30 cm deep.
  • Gully erosion: the removal of soil by water whereby large incised channels (> 30 cm deep) are formed.  The severity of gully erosion may be recorded as minor, moderate, severe or very severe.  Gully erosion processes may include the removal of soil from the land surface by concentrated runoff or the dispersion of unstable subsoils.
  • Stream bank erosion: the removal of soil from stream banks by the direct action of steam flow and/or wind /wave action. Typically occurs during periods of high flow.
  • Wind erosion: the removal and transportation of soil by wind. (See sheet erosion)


In the aquarium, the substrate corresponds to the materials used in the tank that should replicate the natural substrate and natural conditions for the species.


The surface on which an organism lives. Regarding rivers, the substrate corresponds to its bottom, its constituents and sediments. The substrate can affect the biodiversity of a watercourse.


With regard to water, it refers to the fact that it is motionless and still. Stagnant water can be confined, standing, experiencing a low flow or usage.

Because of its poor quality or shallow depth, stagnant water is unusable.


Also called tannic acid, tanin is a yellowish or brownish, bitter organic compound which can be present in roots, wood, bark, leaves, fruit, and other plant tissues. It consists of some derivatives of gallic acid and it a deterrent to herbivores.


Tubercles are skin nodules made of keratin, the same materials as hair, hooves, and fingernails. They are present on species representing at least 15 families of fishes, including even pet goldfish. In many species, tubercles are found only on males during the breeding season and are shed shortly there after. They are often called breeding tubercles for that reason. The main functions for tubercles include species recognition, fighting and defense of spawning territory or nests, and stimulation of breeding females.


In central Amazonia the prevailing floodplain forest is differentiated into nutrient-rich white water “várzea” and nutrient-poor blackwater or clear water “igapó”.

Most white-water rivers have their catchment area in the Andes and are loaded with nutrient-rich sediments. Várzea floodplains cover an area of more than 400,000km2 from which about 75% of this area is covered by forest. The Solimões-Amazon, Purus, Madeira and Madre de Dios are some examples of white-water rivers.


A water body consist in an accumulation of water. Water bodies are classified in different categories on the basis of their size: oceans (further divided in seas), inland bodies of water (as lakes), bodies of water in motion (as rivers, streams, etc.), frozen water bodies.


It refers to a more specific part of the interested water body, which is thus further divided in upper, medium, and lower body part.


With regard to the different sections of the BIOTOPE AQUARIUM Project, the category “Water Chemistry” groups all the information about the condition of water in the given biotope or in the Biotope Aquarium Model.

Under “Water Chemistry” are listed some information and the chemical parameters of the described watercourse. It lists the water type, water colour, water transparency, the concentration of sediments, water temperature, water flow/current, pH, conductivity, GH, KH, and dissolved oxygen.


Colour is one of the organolectic properties of water. Its colour varies with its physical, chemical and bacteriological conditions. Colour can distinguish water in:

  • Clear water: typical of water courses with a good flow. It appears clear and of a greenish colour. The pH is usually neutral or slightly acidic, the conductivity and the presence of dissolved materials is low,
  • Black water: typical of water courses with a slow or no flow. It appears of a dark colour because of the tannins resulting from the decay of the vegetation. The pH is usually acidic and the conductivity low,
  • White water: typical of water bodies that contain high levels of suspended sediments. The pH is usually neutral and the conductivity high,
  • Mixed water: typical of water bodies that go through different environments, so that the water changes properties in the different parts of its course.

/əˈbʌv/ /ˈwɔːtəfɔːl/

A waterfall is an area where water flows over a vertical drop or a series of steep drops in the course of a stream or river.

A waterfall is a part of the river or other water bodies and it is caused by the water’s steep fall over a rocky ledge into a plunge pool below. Waterfalls are also called cascades. The process of erosion, the wearing away of earth, plays an important part in the formation of waterfalls.

A waterfall acts as a natural barrier that many fish species cannot cross. That is the reason why the fish fauna above waterfall might be different from the fish fauna below the waterfall, especially if influenced by tides, like it often happens on the islands of Papua New Guinea. An exception to this is represented by a few fish species who can climb up the waterfall with special adhesive organs, like a few gobies or Balitoridae that uses its suctioning mouth and/or a sucker on its stomach to inch upward against the flow of water.


Water bodies usually have currents, that can be distinguished in surface currents and deep-water currents. When talking about a river, its flow can be lower or higher and determines how and how much water flows. Current is determined by many different factors, among which winds, gravity, water volume, riverbed conformation, etc.

/ˈwɔːtə/ /trɑːnsˈparənsi/

Water transparency is linked to the presence of particles suspended in the water and to the amount of light and sun radiations that can penetrate it and at what depth. The more transparent the water, the deeply sunlight can penetrate, thus enabling plants and organisms on the bottom to survive.


Water is divided in four different types: meteoric water, from rain or snow, surface water, further distinguished in freshwater, brackish water and marine water, and telluric water, as that from springs or aquifers.


Zooplankton are small floating or weakly swimming organisms that drift with water current.