Glossary

54 terms beginning with H · showing 1–40

1. habitat

   The natural home or environment of an organism.

   Used in 805 profiles

2. hang on back filter

   Small, motor-driven, type of external filter that literally hangs over the edge of the aquarium. Unsuitable for larger aquaria and often abbreviated to HOB or HOT (hang on tank).

3. haor

   Wetland ecosystem of which most are located in northeast Bangladesh. The typical form is that of a bowl or saucer-shaped depression and the core haor area is surrounded by hills of the Indian states of Meghalaya to the north, Tripura and Mizoram to the south, and Assam and Manipur to the east. The area is known locally as the 'Haor' or 'Sylhet' basin and floods extensively each year during the annual monsoons.

   Used in 1 profile

4. hard water

   Water containing high concentrations of mineral salts.

   Used in 45 profiles

5. hastate

   Shaped like the head of a spear.

6. head and lateral line erosion

   Severe physical condition relatively common to certain fishes in captivity and also known as hole-in-the-head. Sometimes attributed to protozoan parasites of the genus Hexamita or an autoimmune disorder though these theories remains unconfirmed. Certainly associated with and exacerbated by poor water quality and/or nutrition, however. Initially manifests itself as small lesions, normally on the head of an affected individual, but may also extend along the lateral line and into the unpaired fins. If left unchecked these lesions can develop into larger, whitish pits and the condition may prove fatal. Often abbreviated to HLLE and similar to, but not analagous with, neuromastic pitting. Does not appear to occur in nature.

   Used in 35 profiles

7. head depth

   Greatest vertical depth through the head.

   Used in 9 profiles

8. head length

   Normally a straight-line measurement taken from the tip of the upper lip to the posterior edge of the operculum.

   Used in 68 profiles

9. head width

   The distance between the two widest points of the head.

   Used in 25 profiles

10. headwater

    Tributary stream of a river close to or comprising part of its source.

    Used in 167 profiles

11. heater

    Thermostatically-controlled device used to maintain constant water temperature in an aquarium or pond, also known as a heaterstat. Depending on design, may be installed submersed within the aquarium, sump or substrate (see heating cable) or inline with tubing attached to an external filter. Some types of the latter also have a heating element built in.

    Used in 42 profiles

12. heating cable

    Length of flexible cable buried under the substrate in an aquarium and used to maintain constant water temperature. Also popular in planted aquaria due to the associated circulation of water within the substrate which aids in nutrient exchange between plant roots and the surrounding environment.

13. herbivore

    An organism whose diet consists almost exclusively of vegetable matter.

    Used in 18 profiles

14. herbivorous

    Feeding on plants.

    Used in 83 profiles

15. heredity

    The passing of characteristics or traits from parent or ancestor to offspring or later generations; the sum of such inherited features or their characteristics.

16. hermaphrodite

    Animal or plant possessing both male and female reproductive organs.

17. heterospecific

    Of or belonging to a different species.

    Used in 18 profiles

18. heterotroph

    An organism that cannot synthesise its own food and instead obtains nutrients from complex organic substances, usually animal or plant matter.

19. Hexamita

    Genus of parasitic flagellates, some species of which inhabit the intestines of fishes. May cause head and lateral line erosion.

20. hierarchy

    Series of ordered or groupings or rankings within a defined system. Taxonomy is a form of hierarchy as are the ranked social groupings typical of certain fish species. The latter form of social hierarchy is also known as a pecking order.

    Used in 85 profiles

21. hole-in-the-head

    See head and lateral line erosion. Often abbreviated to HITH.

    Used in 6 profiles

22. holotype

    The single specimen designated as the name-bearing type of a nominal species or subspecies.

    Used in 36 profiles

23. homeostasis

    The ability or tendency of an organism or cell to maintain internal equilibrium by adjusting its physiological processes.

24. homologous

    Exhibiting a a degree of similarity, e.g., in anatomical position, structure, function, or character that may suggest a shared ancestral or evolutionary origin.

25. homonym

    Two or more names of identical spelling, or differing only in suffix, that have been applied to different members of the same taxonomic rank and of which only one can be valid at any given time.

    Used in 2 profiles

26. homoplasy

    A character or trait shared by two or more unrelated taxa. Typically the result of convergent or parallel evolution.

27. horny

    Hard and rough in texture.

    Used in 35 profiles

28. hospital tank

    See quarantine tank.

29. humeral

    Of, relating to, or situated on the humerus.

    Used in 25 profiles

30. humeral process

    Bony process extending posteriorly from the pectoral girdle, above the base of the pectoral fin. Present only in certain fishes.

    Used in 8 profiles

31. humeral spot

    A marking on the body in the area analogous to the humerus, or shoulder. In fishes it's normally located above the pectoral-fin and behind the opercle. There may be more than a single such spot in some species.

    Used in 42 profiles

32. humerus

    The pectoral girdle in most fishes.

33. husbandry

    Agricultural cultivation or production of plants or livestock, especially domesticated varieties.

34. hyaline

    Glassy; translucent; transparent.

    Used in 71 profiles

35. hybrid

    Organism resulting from a natural or artificial cross between genetically-unlike individuals.

    Used in 36 profiles

36. hybridisation

    The process of crossing different species or populations of organisms in order to produce hybrids.

    Used in 115 profiles

37. Hydra

    Genus of freshwater cnidarian existing only in sessile, solitary polyp form attached to the substrate at one end and with a mouth surrounded by up to 12 tentacles at the other. Members are predatory, feeding mostly on small invertebrates, and regarded as pests in aquaria due to their appearance as whitish spots on submerged surfaces and tendency to prey on fish fry.

    Used in 1 profile

38. hydrology

    The scientific study of water, its distribution, properties and effects on and within the Earth's surface and atmosphere.

39. hydrometer

    Instrument used to measure the density of a liquid, normally in the form of specific gravity. Can be inaccurate should calcium deposits form on the swing arm, for example, and generally less reliable than a refractometer.

40. hydrophilic

    Having an affinity for water.