Fish Glossary

by Andreas Iliopoulos and George J. Reclos

Many times you read the description of a fish species in a book or you try to describe your aquarium settings to a friend or through e-mail. This list of terms was compiled to help you use the right term and understand the terms you find in fishy books. It is not completed and it may take years to become a satisfactory glossary. Still, it is a good start.

·         A

·         A – = Gk prefix that indicates the lack of a certain thing or property (i.e aphagous = with no ability to eat, aphotic = with no light)

·         Abdomen = The belly or lower surface of a fish, between the pelvic fins and the anus.

·         abdominal dropsy = A disorder characterized by edema (accumulation of excess fluid) in the abdomen, which causes abdominal swelling and marked protruding of the scales (pineapple look). A variety of diseases can be the underlying cause, including bacterial infection, viral infection, as well as nutritional deficiencies.  Other conditions that produce a swollen abdomen include: overeating, internal worms, and pregnancy. However, none of these result in the marked swelling with protruding scales that is seen in dropsy.

·         Aberrant = abnormal, unusual (for behaviour, organ / tissue function or even form)

·         Abyss = Gk originated word (original Abyssos), which indicates the part of the oceans between 4.000 m and 7.000 m of depth

·         Abyssal plain = the flat regions of the abyss

·         Abyssopelagic = the oceanic zone originated at the abyss

·         Acanthopterygii = (Taxonomy) Class which includes the family Cichlidae

·         Acclimation = the normal (physical) adaptation of organisms in specific environments

·         Acoustic – acoustics = Gk term related to sounds (as a science, including the production, transmission and effects of sounds)

·         Acoustic communication = communication using sounds. Cichlids are also able to communicate with sounds.

·         Active = (for metabolism) the consumption of oxygen of a moving fish

·         Adaptation = the ability of an organism to “fit” or “blend” into an environment. Organisms which cannot adapt to a specific environment or changes that happen to it are usually driven to extinction.

·         Adipose = the fleshy fin without rays that is located behind the dorsal fin and it is present on some primitive fishes (Osteichthys) belong to the CHARACIDAE, SALMONIDAE and SYNODONTIDAE families. The original term means fatty

·         Adult = fully developed fishes (from their morphological aspect and meristic* characteristics), being also sexually matured.

·         Aero – = Gk prefix that indicates relation with the air

·         Aerobic = the ones that need atmospheric air to live, reproduce, function and thrive

·         Akaryotic = cells without nuclei

·         Algae (sin. alga) = Gk word for plants that occur in aquatic environments

·         Algal bed = surfaces covered with algae (usually Sargassum and Turbinaria genera, but also for P. oceanica)

·         Algivore = Organisms feeding on algae.

·         Allele = In the case of diploid organisms (two chromosomes of each type in the nucleus of each cell) this term refers to the gene on the other chromosome which encodes for the same characteristic. Thus in a diploid organism (like humans) there are two alleles. The two alleles may have the same information for this characteristic (homozygous) or different (heterozygous). In this case only one of the genes is expressed (dominant) while the other remains “silent” (recessive). In some cases, there are two different alleles, which are both expressed (e.g. human blood groups, ABO system).

·         Allo – = Gk word for other, different

·         Allopatric population = Similar but slightly different species which do not live in the same place

·         Allopatric speciation = The process by which part of a species adapts to a new environment and finally becomes a different species.

·         Allopatry = see "Allopatric"

·         Allotype = Gk originated word that indicates the differences between the forms of a certain organism of opposite sex, according the holotype (see relevant entry)

·         Altruism = The process in which one organism helps or supports another organism without any (obvious) benefit for it. If there is a benefit for both organisms this is called a symbiosis.

·         Ambush predator = the predator that remains hidden and waits for it prey to approach

·         Amphi – = Gk prefix that indicates both when referring to two different situations or things

·         Amphibians = Organisms which spend part of their life in the water and part on shore.

·         Amphidromous = Gk word for the migratory species, which they migrate from the sea to fresh water bodies and vice versa for breeding purposes

·         Amphihaline = Gk word for aquatic organisms occur both in marine and fresh water bodies

·         Amphipods = part of the crustaceans’ group (for instance the shrimps)

·         Ana – = Gk prefix for back, over

·         Anabolism = part of the metabolism which indicates these biochemical processes that take place when happens energy storage or formation of tissues

·         Anadromous = migratory species, which they migrate from the sea to fresh water bodies for breeding purposes

·         Anaerobic = the ones that do not need atmospheric air to live, reproduce, function and thrive

·         Anal = the region of the anus (as anal fin)

·         Androgens = Male (genetic) hormones.

·         Anisogamy = The difference in the size of the gametes, the small being the sperm (male) and the large being the egg (female)

·         Anus = the exit of the digestive track

·         Anatolia = central region of Turkey

·         Anchovies = fishes belonging to the family ENGRAULIDAE (i.e. herrings)

·         Annelids = worm like invertebrate animals

·         Angular = small bone at the base of the lower jaw, that forms a certain and obvious angle

·         Annual = term which when referring to fishes indicates a species with a life span of less than a year which will spawn only once (i.e. killifishes)

·         Anoxia = Gk term for the absence of dissolved oxygen in a water solution

·         Ante – = latin vernacular adverb that indicates something previous, before

·         Anterior = the former, the antecedent

·         Aplacental = sharks that are viviparous but their young are not connected with their mothers with placenta as happens with other species of sharks.

·         Appendage = large and distinctive projection formed on the body of an animal

·         Aquaculture = organised farm for production of aquatic organisms

·         Aquatic chickens = common name for Tilapia sp.

·         Aquatic tongue = The use of currents in the mouth of many fishes to manipulate their food emulating a “hydraulic” tongue.

·         Articular = the broad bone of the lower jaw

·         Asexual = (for reproduction) breeding process while no gametes’ (see relevant entry) union is taking place

·         Asymmetric = Gk word that indicates lack of symmetry (opposite: symmetric)

·         Auto – = Gk meaning “by itself”.

·         B

·         Bacteria = small single or multicellular (see relevant entry) prokaryotic organisms that multiply asexually (by division or other method). They maybe pathogens.

·         Basal = Gk originated word that indicates what is located towards some base

·         Basin = depression of a water body (i.e. Amazon basin, Mediterranean basin)

·         Basin = an extended depressed area within the sea or a continent

·         Basking sharks = sharks that usually found near the surface, members of the CETORHINIDAE family

·         Bathy – = Gk vorsible that indicates the depth related

·         Bathyal = the benthic environments located between 200 m and 4.000 m of depths

·         Bathydemersal = species that live and feed below 200 m of depth

·         Bathypelagic = Gk term for the species that live and feed at the oceanic* zone (between 1.000 m and 4.000 m)

·         Behaviour = The sum of all the responses of an organism to various stimuli.

·         Benthic = from the Gk word benthos (= bottom); bottom dwelling organisms and environments located at the substratum. (i.e Zoobenthos = benthic animals)

·         Benthopelagic = Gk term for the species that live and feed at the bottom and environments that are bottom associated

·         Bi – = prefix that indicates two times, or number two

·         Billfishes = fishes equipped with long pointed posterior*, members of the ISTIOPHORIDAE family.

·         Biodiversity = variety of species

·         Bioluminescence = the ability of some organisms to produce light by chemical reactions taking place within their tissues

·         Bicuspid = pointed on both sides

·         Bifurcate = separated or divided into two different parts

·         Bilobate = with two lobes

·         Biomass = the amount (on weight terms) of a certain population, or a living stock

·         Biometry = branch of the biology science related to statistics

·         Biparental = of both parents (i.e. biparental care or biparental mouthbrooding)

·         Biserial = having two series, or two rows

·         Bivalves = Gk originated word used for shellfishes with two shells (i.e. oysters, mussels etc)

·         Blastomeres = the individual cell, which is formed during cleavage (see relevant entry)

·         Body length terms = TL for total length (head length for seahorses), SL for the standard length (without the tail), Fl for the fork length, W’D for the width of the discs of skates and rays, OT for the length (height) of sea horses.

·         Boreal = Gk originated geography term for the northern. The one that is adapted in temperate water when is referred to an aquatic organism.

·         Brackish = term referred to animals or water bodies. When the term is used for water means that the specific water has a salt concentration of 0,5 p.p.t. to 30 p.p.t. (0,5 gr to 30 gr of salts per litre)

·         Branchial = Gk originated term related to gills

·         Branchiostegals = Gk originated term for the slim bones which they support the gill membrane

·         Breeding = The process by which two members of the same species but of opposite sex exchange their genetic information and produce their offspring.

·         Broodstock = animals that kept as breeders, animals kept separate to produce offspring

·         Bryozoans = Gk word used to describe small invertebrate animals living in colonies as corals

·         Buccal = term related to the mouth cavity

·         Buffer = a stabilizing chemical agent of a solution. Also buffering capacity indicates the ability of a solution to remain chemically stable

·         Buoyancy = the ability to float and change levels in the water column

·         Bycatch = incidentally caught specimens within the catches of other targets

·         C

·         Cannibalism = Eating members of your own species. Of particular interest when attempting to raise fry. Separation of the fry species known to cannibalise may increase the number of survivors considerably.

·         Cartilage = gristle

·         Cartilaginous = the one with skeleton consisted from cartilages and not bones (see also Chondrichthys)

·         Carnivorus (pl. carnivores) = organisms feeding on animal matter, from latin word carna (possessive case carnae)

·         Carotene = Chemical compound with the ability to produce orange coloration. Found in carots. Of special interest is beta-carotene (pro0vitamin A) which is turned into Vitamin A with the help of sunlight (UV rays).

·         Carotenoid pigments = pigments which will use carotene to produce an orange / red coloration.

·         Catadromous = Gk word that describes migratory species, which they migrate from the fresh water down to the sea for spawning purpose, as for instance the eels

·         Cauda (possessive care caudae) =  (latin)

·         Caudal = see fins

·         Cephalopods = Gk word that indicates invertebrate animals (molluscs) with the feet attached on the head (squids, octopi, cowfishes)

·         Chemical cues = Odor Olfaction

·         Chondrichthys = Gk term that indicates a fish with cartilaginous skeleton (plural Chondrichthyes)

·         Chromosome = Entity in the nucleus of eukaryotic cells (on in the non defined “nucleus” of prokaryotic cells) which acts as a distinct unit during cell division. The chromosome consists of genes, each gene encoding the necessary information for one characteristic. Usually organisms have one set of chromosomes (haploid organisms, n) or two sets (diploid organisms, 2n). Even diploid organisms (like humans) have only one set of chromosomes in their gametes (haploid cells). The number of different chromosomes for one species is constant. For humans it is 23 sets and, since it is a diploid organism this means 46 chromosomes in 23 pairs.

·         Ciguatera = poisoning caused by the flesh of fishes that are toxic to humans

·         Cleavage = molecular separation

·         Cloaca = the chamber that contains the rear opening of digestive track and also the reproductive track of fishes, birds and reptiles

·         Conspecific = organisms belong to the same species

·         Continental slope = the edge of region of a continent from depths of 200 m to 2.000 m.

·         Copepods = Gk word that indicates invertebrate animals (specifically crustaceans), which are either free swimmers or parasites

·         Coralline algae = algae with an external calcareous coverage looking like corals

·         Crustaceans = invertebrate animals (shrimps, lobsters, crabs, prawns, crayfishes)

·         Ctenoid (for scales) = Gk word that describes the ones having a margin resembling combs

·         Cycloid (for scales) = Gk word that describes the smooth rounded scales

·         D

·         Decapods = Gk word that describes invertebrate animals with 10 legs (shrimps, lobsters)

·         Demersal = term referred to the bottom or the bottom dwelling species

·         Dermato – = (Gk) referring or related to the skin.

·         Detritivores = organisms feeding on detritus.

·         Detritus = decomposing plant or animal matter (organic debris)

·         Dichromatism = Usually sexual although not only. In sexual dichromatism the two sexes show different coloration. In some species (e.g. lake Malawi cichlids) the difference may be striking.

·         Digestive system = the system in which digestion takes place. Includes the mouth (adj. stomatic), the pharynx, the oesophagus, the stomach, the small and large intestine and the anus. Several glands, which secrete enzymes necessary for digestion, are also included in the digestive system. Such enzymes are secreted by the salivary glands, the bile and the pancreas. In fishes the intestine is connected to the swim bladder.

·         Dimorphism = Gk word that is used to indicate morphological differences between the two sexes

·         Diploid = organisms with two chromosomes of each type in the nucleus of each cell

·         Disease = Malfunction of a tissue, organ or system of a living organism due to an external or internal causing factor.

·         Diurnal = organism active by the light hours of the day (opposite nocturnal)

·         Diurnal migration = vertical daily migrations of some specific aquatic organisms. Usually these are done for avoiding predators at the day and for preying on their food at night.

·         Dominant = ruling. In the case of genes, the one which is expressed. Opposite: recessive.

·         Dorsal = the back, upper part of the body

·         Duct = Pore, canal, tube. Usually it is an opening through which a liquid is “exported” in a cavity.

·         Ductus pneumaticus = the duct which connects intestine and swim bladder (see relevant entry)

·         E

·         Echinodermata (sin. echinoderma) = Gk word used for a group of invertebrate animals that carry spines on their bodies as coverage (i.e. urchins)

·         Ecosystem = Ecological System.

·         Electrosensing = the ability of certain animals to sense electric stimuli (sharks, for instance)

·         Embryon = Gk word for the foetus (also embryo) - wrigglers

·         Embryonic = the life stage of foetus

·         Epi – = (Gk) referring or related to the top or on top of.

·         Epidermis = (Gk) the outer layer of the skin

·         Epipelagic = Gk word that indicates the upper region of the water column that the light reaches

·         Estuary = river mouth with brackish water or with water from the mix of the fresh and the marine water

·         Eu – = Gk prefix meaning much or well shaped.

·         Eury – = Gk prefix meaning wide or a wide range.

·         Eurybathic = Gk word that is used to notice a species’ abundance in a wide range of depths

·         Euryhaline = Gk word that describes organisms that may be encountered in a wide salinity range (opposite – stenohaline)

·         Eurythermic = Gk word that indicates tolerance to a wide range of temperatures (opposite – stenothermic)

·         Eutrophic = Gk word that describes environments rich in nutrients and aquatic vegetation (opposite – oligotrophic)

·         F

·         Fauna = the animals of an environment

·         Fecundity = number of eggs that a ♀ animal lays

·         Filament = the fine and elongated slender appendage

·         Fins = skin formations consisting from membranes and rays (see relevant entry), Anal fin = the fin located at the anus (see relevant entry). Caudal fin = the fin of the tail (concave, forked, rounded in shape), Dorsal fin = the fin on the back, Pectoral fin = the fins on the chest or thorax (see relevant entry), Pelvic fin = the fins on the pelvic (see relevant entry) region

·         Filament = the fine and elongated slender appendage

·         Fin = see entries: Anal fin, Caudal fin, Dorsal fin, Pectoral fin, Pelvic fin

·         Flora = the plants of an environment

·         Frontal = of the forehead, bone on the scull

·         G

·         Gametes = the cells that are involved in reproduction (eggs and sperm)

·         Gene = The part of the chromosome which encodes a single characteristic. See also “allele”.

·         Genetics = branch of the biology, involved with breeds and their characteristics (a greek word)

·         Genotype = the sum of all information encoded in the chromosomes of an organism. See also “phenotype”

·         Genus (plural genera) = latin word for the breed or the parentage (ge – nus, ge – ne – ra, as in game)

·         Gills = the breathing organs of most of the fishes

·         Gill arch = a bow like structure with rakers (comp like structure) and filaments (see relevant entry)

·         Gonads = Gk word that is used to indicate the animals’ internal and plants’ external reproductive organs

·         Gonopodium = Gk word that is used for the external organ of ♂♂ livebearer fishes that is used to transfer sperm into the body of the ♀♀. In fact it is the modified anal fin

·         Gregarious = organisms living in groups

·         H

·         Hepatic = Gk for liver related.

·         Herbivorus (pl. herbivores) = organisms feeding on plant matter Hermaphrodite = Gk word for the ones having both sexual organs

·         Hermaphroditic = Gk word used to describe the case when both sexes are present on the same organism at the same time (synchronous hermaphrodite), or at different time (successive hermaphrodite). When the ♀ sex is the first then we are talking for a protogynous hermaphrodite; and vice versa for a protandric hermaphrodite (in both cases there are Gk words)

·         Hetero – = Gk prefix that indicates something depending on external factors

·         Heterocercal = asymmetry of the caudal fin (same as melanocercus = black or dark coloured tail)

·         Heterothermic = greek word that indicates organisms that their body temperature depends on the ambient temperature

·         Heterozygote (-ous) = The two alleles (for the same characteristic) encode different information. See also “allele”

·         Holotype = the original single selected organism, which was used as the standard specimen which will bear the new name of the species

·         Homozygote (-ous) = Both alleles (for the same characteristic) contain the same information. See also “allele”

·         Hybrid = Offspring derived from two different species. Recently there have been "hybrids" produced by mixing more than two species. Hybrids may be fertile and cross breed with their own kind or any other suitable species in the tank. Species which show similar markings (melanin pattern) are particularly prone to hybridization.

·         Hybridization = (introgressive , speciation)

·         Hydro – = (Gk) meaning "water related"

·         Hydrozoans = Gk word that describes a group of invertebrate animals (i.e. medusas)

·         Hyper – = Gk, over or excessive (e.g. hyperdominant)

·         Hyperdominant = In a tank usually refers to the individual who rules all other tankmates irrespective of the species / sex they belong to.

·         Hypo – = Gk, under or recessive.

·         Hypothesis = Gk (hypo+thesis). Assumption. A hypothesis has to be proven to become a thesis.

·        I

·         Immune system = A system which responds to any foreign structure entering the body. The immune system works in two ways resulting in humoral and cellular immune responses. Cellular immune responses are characterized by specificity and the ability to distinguish self from not-self. The education of those cells is thought to take place at an early stage of life. In case of malfunction of the immune system, self structures may be wrongly recognized as “non-self” and subsequently attacked. This results in autoimmune disorders (e.g rheumatoid arthritis and multiple sclerosis)

·         Immunity = The ability of an organism to withstand an invasion of a pathogen without getting sick. This is because of the presence of memory cells able to recognize knock down the invader in a very short time or the presence of antibodies which enable the killer cells to eliminate the pathogen. This may be the result of a previous encounter with the same pathogen (natural active immunity), acquisition of the antibodies in a natural way like breast feeding (passive natural immunity), the inoculation with inactivated pathogens or their antigens (artificial active immunity – vaccination) or the supply of antibodies developed in another host (artificial passive immunity). Only active immunity results in memory cells. The water conditions, the variety and good quality of suitable food as well as the absence of stressing factors are key elements for a strong immune system of any fish.

·         Infection = the onset of a disease following the entrance of a pathogen.

·         Intestinal, Intestine = Referring to the last part of the digestive system. Intestine includes small and large intestine and connects the stomach to the anus. The largest part of food absorption takes place in the intestine. Intestinal bacterial infections are common and, if not treated quickly, fatal.

·        J

·         Jaw locking = Act of aggression usually between males of the same species although not necessarily limited to that. Two fishes will lock their jaws and test their strength. In some cases this may result in jaw dislocation.

·        K

·