Fish Glossary

Adipose Fin: Rayless fin on the midline of the fish's back, between the dorsal and caudal fins.


Air Bladder: See "swim bladder."


Anadromous: Ascending rivers from the sea for breeding.


Anal Fin: The fin on the underside of a fish, nearest to the tail.


Annulus: Ringlike markings on the scales (or spines and vertebrae) of a fish that are used to determine age.


Anterior: Placed on or near the head or front of an animal, the opposite of posterior.


Barbel: A slender, flexible projection near the mouth of certain fish. It is used for smell and taste.


Body Depth: The measurement of a fish from top to bottom (backbone to belly).


Branchiostegal Rays: The bones that support the gill membranes.


Carnivorous: Feeding on animal tissue.


Caudal Fin: The tail fin.


Caudal Peduncle: The part of a fish's body located between the anal fin and the beginning of the caudal fin.


Cleithrum: The large bone that extends from the base of the pectoral fin and forms the posterior edge of the gill chamber. This bone is used to determine the age of some fish (for example, muskies and northern pike) because each year the fish's body adds a new layer of bone. Also see otolith.


Crustaceans: A group of mostly aquatic animals that have an exterior skeleton and antennae; some
examples of crustaceans include shrimps, lobsters, crabs, and water fleas.


Dorsal: Placed on or near the back of an animal, especially on the backbone. It is the opposite
of ventral.


Dorsal Fin: The fin or fins on the top (dorsal) side of a fish. Some fish (like trout) have only one
dorsal fin. Others (like sculpin) have two dorsal fins.

Food Chain: An arrangement of organisms in an ecosystem whereby the “bottom” level of
organisms are eaten by the next higher level, which themselves are eaten by the next
higher level, and so on.

Fry: Newly-hatched young fish.

Gill Cover: The bones of the fish's head that cover the gills.

Gill Filaments: The threadlike structures connected to the gill arches, used for respiration.

Gill Rakers: Comblike projections that extend from the gill arches.

Hypural Notch: The place on a fish's body between where its backbone ends and its tail begins.

Lateral Line: A row of pores on the side of a fish's body that open into tubes containing organs that
are sensitive to low vibrations.


Lateral Line Canal System: A pressure- and sound-sensitive tubular system found in most fish. It consists of the pored openings on the head and lateral line.

Length, Standard: The total length of a fish from head to tail, not including the tail.

Length, Total: The total length of a fish from head to tail, including the tail. Measurements are usually
given in total length, unless stated otherwise.


Mandible: The lower jaw.


Mandibular Pores: Small sensory openings on the underside of the lower jaw (mandible).

Maxillary: The upper jaw (especially the lateral bones).

Opercle (or Operculum): The large bone that serves as the covering of the gills of a fish.


Opercular Membrane: The thin membrane along the posterior edge of the gill cover.

Origin: The point at which the part of the fin nearest the head meets the fish's body.

Otolith: An ear stone (or calcareous concretion) in the inner ear of a bony fish. Each year, a new concretion (layer of bone) is added, which can be used to measure age. Also see cleithrum.

Pectoral Fins: Fins located directly behind the head of the fish. They come in pairs.

Pelvic Fin: A set of fins on the underside (belly) of a fish that are usually placed between the
pectoral fins and anal fin.

Posterior: Placed near or on the tail or end of an animal, opposite of anterior.

Rays: Flexible supports for a fin.

Scales: Small, flat plates that fit together to form the external body covering of a fish.


Sensory Pores: The tubular openings found in the lateral line canal system.

Spawn: To produce or deposit eggs; as a noun, spawn refers to the eggs of aquatic animals like
fish or amphibians.

Stocking: Adding fish to a body of water, such as a lake, pond, or stream.


Sucking Disk: The extended mough region (usually armed with rasping teeth) of an adult lamprey.


Swim Bladder: A sac containing gas and air, present in the upper part of the body cavity, that aids in creating buoyancy and in the respiration of some fishes. (Also called an "air bladder.")

Tributary: A stream or river that flows into a larger stream or river or into a lake.

Upwelling: The process by which colder, deeper water is brought to the surface.


Ventral: Placed near or on the belly or lower surface of an animal, opposite of dorsal.

Vermiculations: Wormlike irregular or wavy lines.

This page is Bobby Approved.

Fish Glossary

Opercle (or Operculum)