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Aquarium Tropical

glossary & Fish Terms

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Marine and Freshwater Tropical Fish
and Aquarium Glossary of Terms

A glossary of terms and words and their meanings when used for
saltwater and freshwater aquarium fish.

adipose fin - The small fin located between the dorsal fin and
the caudal fin.

amyloodinium - Amyloodinium ocellateum is commonly called
Oodinium, Marine Velvet, or Saltwater Ick.

anal fin - Single fin mounted vertically below the fish.

anthostele - The lower part of the polyp, often stiffened, into
which the distal portion of the polyp, the anthocodia (which
includes the mouth and the eight tenacles) is withdrawn. The

barbels - Barbels are the whisker-like appendages found on both
sides of the mouth of all catfish.

benthic - Benthos and benthic refers to living on or under the
substrate at the bottom of the ocean. Sessile means the organism
is attached to the substrate. Pelagic refers to living in the
water of the ocean above the bottom. Pelagic organisms usually
have some ability to move around.

brackish - water that is neither fresh nor saltwater, but is
somewhere in between. In nature this occurs at the mouths of
rivers and swamps near the sea. Some fish live in salt water but
are spawned in brackish or fresh water and vice versa.

Byssus Gland - The structure in clams that produces fibrous
threads (byssus) that attach the clam to substrate. Sometimes
permanent although more usually temporary attachment of tough
organic threads secreted from a gland in the foot of the clam.

carapace - A bony or hard shell that covers part or all of an
animal. Turtles, crabs, and boxfish are good examples.

caudal - The single fin mounted vertically at the rear of the
fish. The tail fin.

caudal penduncle - The part of the body which attaches the caudal
(tailfin) to the body. The surgeonfish's spines are located on
the caudal penduncle

coelenterate - an aquatic animal of the Phylum Coelenterata which
is characterized by a central mouth usually surrounded by
tentacles bearing stinging cells, includes sea
anemones, corals, and jellyfishes.

coenenchyma - the tissue of a zoanthid that surrounds the polyps.
Consists of mesoglea and may have sand imbedded in it.

comensal - A relationship where two or more different kinds of
animals live together and one benefits while the other does not.

conspecific - Refers to animals of the same species.

cryptocaryon - Cryptocaryon irritans is a parasitic infection
where white spots appear on the body and fins. Fish will scratch
themselves against rocks and breathing may become rapid if gills
are affected. Treatment can be done by copper or other
anti-parasite remedies, but this is incompatible with inverts.
Cleaner shrimps and wrasses will remove the parasites, but may
not keep up with a major infestation. Cryptocaryon is often
referred to as the marine equivalent of the freshwater white spot
disease, Ichthyophthirius, or Ick.

cyanobacteria - Cyanobacteria is commonly referred to as red
slime algae by hobbyists although it is not really an algae. It
is a bacteria. Poor water quality with excessive nutrients are
the usual causes.

detritus - Grayish piles of organic compounds that accumulate in
the aquarium. Commonly will contain fish wastes, fragments of
rock, leftover food, among other things. Usually detritus will
accumulate in low water flow areas, sumps, etc.

detrivores - Animals that eat detritus. Common detritvores are
urchins, stars, hermits, etc.

diatom - A diatom is any of a class of microscopic one-celled
algae having walls of silica consisting of two interlocking

diurnal - An organism that is active during the day, and sleeping
at night.

dorsal fin - The fin directly on the top of the body
Some fish have two dorsal fins one directly behind the other.

endemic - Restricted to a particular place. Means the animal
lives in a certain place and nowhere else.

gonopodium - Particular to the Live-bearing tooth carps, the
gonopodium is the pelvic fins of male fish that have been
converted into genital organs.

gorgonian - A Gorgonian is a tropical or subtropical octocoral
with upright branchy plant-like or fan-like growths and a
skeleton made of a horny organic material. For example, the Sea
Fans (Scientific names: Gorgonia ventalina, G. flabellum, G.
mariae, Pacifigorgia spp.)

head and lateral line erosion - Also known as hole-in-head
disease and lateral line disease. A fish with this condition will
develop holes in its' head and sometimes along its' lateral line.
The main cause is nutritional deficiency, especially vitamin C.
Stress and poor water quality also play a role. Untreated cases
will cause disfiguring or death. To combat and cure, ensure good
water quality and provide vitamin enriched foods, especially
vitamin C.

hermatypic - Refers to organisms that contain zooxanthellae. This
usually means they need strong light to thrive.

hermaphrodite - Refers to both male and female in the same

heterospecific - Refers to animals of different species. If two
or more animals are heterospecific, it means they are not the
same species.

hydrometer - A Hydrometer is an instrument used to determine the
specific gravity of a fluid. Hobbyist grade hydrometers are
temperature corrected to read the specific gravity at around 77F
(25C) because specific gravity is temperature dependent.

ichthyophthirius, or Ick

invertebrate - Commonly called inverts by many in the hobby.
Invertebrates are animals without backbones like anemones,
corals, shrimps, snails, and crabs.

kalkwasser - German word meaning calcium water, kalkwasser is a
mixture of calcium hydroxide in water. The ph is very high
(around 12.0) and it is used as makeup water to replace calcium
used by hard corals and clams to build calcerous skeletons.

lateral line - The lateral line is a line of perforated scales
along the flanks of a fish which lead to a pressure-sensitive
nervous system. This enables the fish to detect vibrations in the
surrounding water caused by other fish and their own reflected
vibrations against obstacles.

littoral - Pertaining to the edge of the lake, near the shore.

Mantle - Large, pigmented fleshy portion of tridacnid clams that
is exposed to the light by gaping of the shell valves. Also
called siphonal tissue. Also, the coral tissue in fleshy polyps
(e.g. Catalaphyllia).

mimicry - When an animal mimics, or copies the appearance of
another animal in order to gain an advantage, like camouflage or
a better defense. A good example is the marine fish, Mimic tang.

nauplii - The larval stage, of a crustacean such as the brine
shrimp, Artemia salina or brine shrimp. "Artemia nauplii" are
commonly used as a first food for fish.

nematocysts - The cells at the tip of an anemones' (corals)
tentacles which "sting" when touched.

octocoral - Octocorals have eight tentacles on each polyp. There
are many different forms which may be soft, leathery, or even
those producing hard skeletons.

omnivore - Animals who eat both meat and vegetables like marine

oviparous - Producing eggs which are fertilized, develop and
hatch outside the body.

ovoviviparous - Producing eggs (usually with yolk) that are
fertilized internally. Hatching may occur internally or external
to the mother.

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.

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.

pectoral fins - The anterior or dorsalmost paired fins of fishes.
They correspond to the anterior limbs of the higher vertebrates.

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

plankton - Plankton are the drifters of the sea. Although they
may have some form of locomotion they are mostly carried by water
currents. Plankton is divided into macroplankton (jellyfish,
sargassum weed) and microplankton, organisms that can only be
seen by a microscope. The microplankton is divided into
zooplankton, tiny marine animals, and phytoplankton, or plants.
Most fish start their lives as small animals in the plankton.

polyp - A polyp is the living unit of a coral.

predaceous - This means the animal will hunt and eat other
animals. The old rule comes to mind, big fish eat little fish!

protozoan - A protozoan is a single-celled, microscopic (usually)
organism. For example, an amoeba.

sessile - Sessile means the organism is attached to the substrate
at the bottom of the ocean and therefore cannot move around.
Pelagic refers to living in the water of the ocean above the
bottom. Pelagic organisms have the ability to move around.
Benthos and benthic refers to living near or under substrate at
the bottom of the ocean.

specific gravity - As a hobbyist definition, specific gravity is
the amount of salt in the water. See the hydrometer definition
above for more information. Specific Gravity of seawater ranges
from 1.022 to 1.030.

symbiotic - A relationship where two or more different kinds of
animals live together and both benefit in some way from the
other's company. The most famous example is the clownfish and the

Siphon - The inhalent and exhalent siphons of tridacnid clams are
used to allow for gas exchange and to expel wastes.

sweeper tentacle/polyp - A coral tentacle or polyp that has an
increased number of nematocysts and elongates in order to 'sting'
neighboring corals and sessile invertebrates. See the Frogspawn
coral, Euphyllia divisa for a picture of sweeper tentacles.

taxonomy - The classification of organisms in an ordered system
that indicates natural relationships.

ultraviolet (UV) light - Ultraviolet is a high energy, short
wavelength of light. It is shorter than violet in the visible
spectrum and on the border of the x-ray region.

Umbo / Umbones (plural) - The apparent "apex" or "beak" of each
valve around which "radial" growth has proceeded.

UV sterilizer - A UV Sterilizer is a device that uses ultraviolet
light to make the water treated with it free of microorganisms
which may cause disease.

Weber's apparatus - described in 1820 by E. H. Weber, the Weber's
apparatus connects the hearing organ with the swim bladder where
it operates as a sounding board thus amplifying sounds.

zooxanthellae algae - (zo-zan-thel-ee) Zooxanthellae algae are
tiny plants called dinoflagellates (single-celled microscopic
organisms which belong to the Protista kingdom) that live
symbiotically with corals, tridacnid clams, and some sponges.
The algae provides food for the host and in return gets the
nitrogen, phosphorous, and carbon dioxide it needs to grow. The
scientific name is Symbiodinium spp

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