Dichotomous Key Glossary (Fish)

Definitions

Acuminate

Somewhat pointed, but not as extreme as lanceolate

Abdominal

Referring to the belly region.

Accessory Sensory Line

One or more series of sensory pores that diverge from the main lateral line. In soles of the genus Gymnachirus, these occur at right angles to the main lateral line on the right (eyed) side.

Adipose

Referring to fatty tissue. For example, adipose eyelid——a transparent covering over the eye of some fishes——-or adipose fin.

Adnate

Attached

Air bladder

Swim bladder, a gas filled membranous organ responsible for buoyancy in many fishes. Some fish use their air bladder as a lung, and some others use it as a sound producing organ.

Ambicolorate

In the flatfishes, part or all of the blind side having the same or similar pigment as the eyed side.

Anadromous

Living in the sea but entering fresh water to spawn.

Anal Fin

Circled on figure.

Angulate

Having definite corners, forming an angle, with at least one point.

Antitropical

Distributed in both northern and southern temperate zones, but not common in the tropics.

Axil

The rear side of the pectoral fin base; the “armpit”.

Axillary scale (Axillary Process)

An elongate structure at the base of the pectoral or ventral fins in some fish.

Barbel

A threadlike structure on the head; usually sensory

Bathypelagic

Pertaining to or living in the deep waters of the open ocean (depths usually greater than 1000 meters)

Benthic

Referring to the sea bottom.

Bifurcate

Branching into two lobes or sections.

Bony Stay

A prominent bony ridge running from a suborbital bone to the preopercle.

Branchiostegal membrane

A membrane connecting the gill cover or opercle with the throat.

Branchiostegal Ray

Slender bones in the branchiostegal membrane.

Buckler

Large, multi-spined structure in the skin of batfishes.

Canine

A slender, rounded, pointed tooth for holding or tearing.

Catadromous

Living in fresh water but entering the sea to spawn.

Caudal Fin

See Figure

Caudal Peduncle

The region between the last ray of the anal fin and the base of the caudal fin.

Chest

The ventral area just behind the throat.

Ciguatera

A disease of the nervous system caused by eating certain tropical fishes.

Circumtropical

Occurring around the world, in all oceans, in the warm areas extending from the equator to approximately 20 to 30 degrees N and S.

Cirrus

A fleshy appendage, usually on the head or tips of the fins.

Compressed

Laterally flattened.

Corselet

Covering of enlarged, thick scales on the anterior body of some scombrids (mackerel and tuna).

Ctenoid Scale

See photo

Cusp

The base of a tooth, the region where it is attached.

Cutaneous Fold

A low, finlike fold on the tails of rays.

Cycloid Scales

See photo

Deciduous

Tending to shed or break off.

Denticle

Check photo

Disc Lamellae

In remoras, the flattened, overlapping folds in the sucker, actually modified dorsal rays.

Distal

Remote from the point of origin or attachment.

Dorsal

Referring to the back.

Dorsal Fin

see photo

Dorsum

The upper (or dorsal) portion of the fish’s body.

Electrophoresis

One of several molecular techniques used to demonstrate genetic similarities or differences between organisms.

Emarginate

Having the margin indented but not so deeply as to be forked.

Entire

Whole, complete, or smooth.

Epipelagic

Pertaining to or living in the surface waters of the open ocean (depths usually greater than 200 m).

Esca

The fleshy “bait” at the end of the illicium of frog-, goose-, and batfishes.

Estuary

An area where fresh water meets sea water.

Euryhaline

Capable of withstanding large changes in salinity (salty concentration).

Exserted

Extending beyond an otherwise even margin.

Extralimital

Distributed outside the range. The term may be applied to the range of a species or other taxonomic group or to the coverage of a book, paper, or other report.

Falcate

Sickle shaped

Fin

Median or paired structure, usually membranous and supported by soft rays or spines. Fins may be variously modified into other structures such as sucking discs or “fishing poles”.

Adipose Fin

A fleshy median dorsal fin without spines or rays.

Anal Fin

A median fin on the ventral surface between the anus and the base of the tail.

Caudal Fin

The tail fin; the median fin at the base of the tail.

Dorsal Fin

A median fin on the dorsal surface; it may be single or divided into two or more fins.

Finlets

Detached median fins following the dorsal or anal.

Pectoral Fin

Paired fins on either side of the body, usually near or just behind the gill opening; these correspond to the arm or foreleg of terrestrial vertebrates.

Pelvic or Ventral

Paired fins below or behind the pectorals, near the anus (abdominally inserted), under the pectorals (thoracically inserted), or in advance of the pectorals (jugular).

Finlet

Typically found in fast swimming fishes, they are thought to improve the hydrodynamics of these species.

Forked

Divided into two parts or branches.

Fusiform

Streamlined “cigar shape” typical of most fishes.

Ganoid Scale

See Photo

Gill Arch

Unit of respiratory structures on either side of the pharynx.

Gill Filament

Slender respiratory structures that compose the posterior part of the gill arch where gas exchange occurs.

Gill Membrane

See Branchiostegal Membrane

Gill Rakers

Usually, stiff projections on the inner or anterior surfaces of the gill arch, used for straining food.

Gular Plate

A bony median plate between the lower jaws of some fishes.

Head (Head Length)

The region from the tip of the snout to the posterior edge of the gill cover.

Heterocercal Tail

Look at figure.

Homocercal Tail

See photo

Humeral

Pertaining to the shoulder region, just behind and above the pectoral fin in most marine fishes.

Hyoid

Of or pertaining to the tongue.

Hypural Plate

Posterior end of the vertebral column, noticeable as a vertical crease when the tail of the fish is bent forward.

Illicium

Modified dorsal spine that serves as the “fishing rod” in angling fishes; see also ESCA

Incisor

A long but sharp-edged tooth for scraping or cutting.

Interhaemal

Bones connecting the ventral vertebral arches.

Interorbital

Region (or bone) on top of the head between the eyes.

Intromittent Organ

A modified structure (fin) in the male of fishes with internal fertilization that is used for transfer of sperm to the female.

Isocercal tail

Look at photo

Isthmus

Fleshy region extending forward on the throat between the gills.

Jugular

Of or pertaining to the throat.

Keel

A raised ridge, often on a scale or on the caudal peduncle.

Lachrymal Plate

In searobins a bone under the eye and above the maxilla.

Lanceolate

Tapering to a long, lancelike point.

Lateral line

A line of modified scales with pores in them connected by tubes usually running the length of the fish from behind the gill opening to the base of the caudal fin. The pressure-sensitive pores, but not the scales of the lateral line, usually extend onto the head of the fish and sometimes onto the caudal fin as well. The position, shape, and number of scales in the lateral line is of taxonomic importance in many fishes.

Lateral Scale Rows (Vertical scale rows)

The number of scales in a vertical row between the gill opening and the base of the caudal fin, used instead of the lateral line scale count in fishes that lack a lateral line.

Length

Measured in various ways.

Fork Length

From the tip of the snout to the fork of the caudal fin. Standard length (sl). From the tip of the snout to the tip of the hypural plate. Total length (TL). From the tip of the snout to the tip of the caudal fin.

Leptocephalus

A laterally flattened, transparent larval stage of eels, bonefish, tarpon, and ladyfish. It has a small head and decreases considerably in size and body depth during metamorphosis.

Lunate

Deeply forked, with curved branches.

Mandible

Lower Jaw

Maxilla

One of the bones comprising the upper jaw.

Medial

Near the centerline of the body.

Melanophore

A dark colored pigment cell.

Meristic

Pertaining to the number of serial parts, for example, fin rays or lateral line scales.

Mesopelagic

Pertaining to or living in the midwaters of the open ocean (depths usually 200-1000 m).

Molar

A short blunt tooth for crushing.

Nape

The posterior most part of the head just before the dorsal fin.