Fish External Morphology, Musculature, and Skeleton Vocabulary

Vocabulary flashcards covering external morphology, body measurements, fins, scale types, cranial and trunk musculature, and skeletal structures of fishes.

Fusiform

A streamlined body shape with an elliptical to round cross-section and a narrow caudal peduncle, capable of constant swimming at relatively high speeds.

Compressiform

A laterally flattened and deep-bodied body shape characteristic of highly maneuverable fishes.

Sagittiform

A slender body shape with posteriorly located fins, characteristic of ambush predators capable of fast acceleration.

Anguilliform

An elongate and slender body shape characteristic of most eels.

Filiform

A body shape that is very elongate and very slender, thread-shaped.

Globiform

A short, round, robust, globe-like body shape typical of slow swimmers or obligate substrate dwellers.

Depressiform

A dorso-ventrally flattened and wide-bodied shape usually found in fishes closely associated with the substrate.

Total length (TL)

The distance from the tip of the snout to the tip of the caudal fin.

Standard length (SL)

The distance from the tip of the snout to the base of the caudal fin, taken only on teleost fishes possessing homocercal caudal fins.

Fork length (FL)

The distance from the tip of the snout to the posteriormost point of the mid-section of the caudal-fin membrane, measured on teleost fishes possessing forked or lunate homocercal caudal fins.

Body depth (BD)

The maximum depth of the body of a fish.

Caudal peduncle length (CPL)

The distance from the posteriormost point of the anal-fin base to the base of the caudal fin.

Caudal peduncle depth (CPD)

The minimum depth of the caudal peduncle.

Head length (HL)

The distance from the tip of the snout to the posteriormost point of the operculum.

Snout length (SnL)

The distance from the tip of the snout to the anterior margin of the eye.

Eye diameter (ED)

The horizontal distance between the anterior and posterior margins of the eye.

Inferior mouth

A mouth position located on the underside of the head, typical of benthic feeders that consume prey on or close to the substrate.

Superior mouth

A mouth position directed upwards, typically found in benthic lie-and-wait predators or surface feeders.

Supraterminal mouth

A mouth position intermediate between terminal and superior.

Terminal mouth

A mouth position located at the anterior tip of the head, most commonly found in active predators.

Barbels

Long delicate filament-like structures situated around the mouth and snout used as tactile and/or taste (chemoreception) organs.

Cirri

Short fleshy appendages located in the skin of the head and body, usually involved in camouflage.

Operculum

A shield-like structure that covers the gill slits in bony fishes, composed of up to four separate bones: opercle, preopercle, subopercle, and interopercle.

Superficial neuromasts

Mechanoreceptor organs located on the surface of the skin of the head and body used to detect water movement.

Cephalic lateral line

A series of canals borne on dermal bones of the cranium containing canal neuromasts that open via pores to detect pressure waves.

Spiracle

A small opening found posterodorsal to the eye in cartilaginous fishes and certain basal bony fishes, interpreted as a vestigial gill slit.

Ampullae of Lorenzini

Electroreception organs filled with a gelatinous substance, visible as tiny dark pores on the head and snout of cartilaginous fishes and paddlefishes.

Ceratotrichia

Thick collagenous rods that internally support the fins of cartilaginous fishes.

Actinotrichia

Thin, hair-like threads of collagen supporting the fins of bony fishes in juvenile stages.

Lepidotrichia

Bony fin rays that replace actinotrichia in ray-finned fishes as they grow.

Soft rays

Segmented lepidotrichia found in all fins that may be branched or unbranched.

Spinous rays

Unsegmented, unbranched, and often hard and pointed lepidotrichia that are solid, singular structures.

Heterocercal caudal fin

An externally asymmetrical caudal fin in which the upper lobe is much larger than the lower lobe.

Diphycercal caudal fin

An externally symmetrical caudal fin supported by a symmetrical skeleton in which the vertebral column continues into the center of the single lobe.

Homocercal caudal fin

An externally symmetrical caudal fin in which the vertebral column is foreshortened and supported internally by an asymmetrical skeleton.

Finlets

Small, triangular-shaped median fins located along the dorsal or ventral midline posterior to the dorsal and anal fins and anterior to the caudal fin.

Adipose fin

A small, ray-less fleshy fin supported solely by actinotrichia, located between the dorsal and caudal fin in groups like Salmonidae and Siluriformes.

Placoid scales

Scale type present only in cartilaginous fishes, composed of a basal plate, an outer layer of dentine, and an inner pulp cavity.

Ganoid scales

Rhombic-shaped scales composed of a hard inorganic enamel-like substance called ganoine, forming interlocking ridges along the body.

Elasmoid scales

Thin, flexible scales composed of a thin bony layer and a thin collagenous layer, lying in scale pockets in the dermis.

Cycloid scales

Ovoid to circular elasmoid scales that lack projections along their posterior edge.

Crenate scales

Spined elasmoid scales characterized by crenae, which are projections originating from the main body of the scale formed by uneven growth along the posterior edge.

Spinoid scales

Spined elasmoid scales characterized by spines projecting posteriorly and sometimes laterally as continuations of the main body of the scale.

Ctenoid scales

Spined elasmoid scales classified by small, discrete spines (cteni) formed from separate ossifications located along the posterior margin.

Scutes

Enlarged, highly modified scales with sharp edges, most commonly encountered along the ventral midline of Clupeiformes.

Adductor mandibulae

One of the largest cranial muscles in fishes, generally involved with closing the mouth.

Myomeres

Segmentally arranged blocks of trunk musculature separated by connective tissue sheets called myosepta.

Epaxial muscles

The dorsal muscle mass located above the horizontal septum.

Hypaxial muscles

The ventral muscle mass located below the horizontal septum.

Red lateral muscle mass

A shallow muscle mass in bony fishes straddling the horizontal septum, utilized during steady, prolonged swimming activity.

Interradialis muscles

Caudal-fin muscles running diagonally across the bases of the caudal-fin rays that serve to pull the rays together.

Hypochordal longitudinalis muscle

A caudal-fin muscle located anterior to the interradialis muscle that runs to the bases of the rays in the upper caudal-fin lobe.

Erectores muscles

Fin-ray muscles located anterior to the ray they move that function to erect the fin rays.

Depressores muscles

Fin-ray muscles located ventrally to the rays that function to depress the fin rays.

Inclinatores muscles

Fin-ray muscles located typically between depressores muscles that function to incline the fin rays side to side.

Chondrocranium

The endoskeletal component of the skull that encloses the brain and inner ears, composed entirely of cartilage or endoskeletal bone.

Dermatocranium

The portion of the skull composed entirely of exoskeletal or dermal bones that develop in the dermis without a cartilaginous precursor.

Neurocranium

The part of the skull that protects the brain and sense organs, composed of the chondrocranium and select dermatocranial elements.

Opercular series

The set of four dermal bones supporting the operculum in bony fishes: the opercle, preopercle, subopercle, and interopercle.

Basipterygium

One of a pair of wedge-shaped endoskeletal bones forming the pelvic girdle in bony fishes.