Fish Glossary
Taken From: [A.J. McClane, McClane's Field Guide to Freshwater Fish of North America, Henry Holt and Company, New York, 1978]
Adipose Fin A small fleshy fin without rays located dorsally on the caudal peduncle. It is typical of the salmonids but occurs on other species.
Ammocete The larval stage of a lamprey.
Anadromous Any fish that migrates from the sea into freshwater rivers for the purpose of spawning. Some anadromous species are the salmon, striped bass, alewife, and shad. Fishes that migrate in the reverse direction from freshwater into the sea for their spawning are catadromous.
Anal Fin The unpaired or single fin on the ventral surface of the body.
Andate Attached to, or grown together.
Anterior Toward the front; the opposite of posterior.
Axil The region behind the pelvic or pectoral fin base.
Axillary Process An elongate structure at the base of the pelvic or pectoral fins.
Band A diagonal or curved marking on a fish's body.
Bar A vertical marking on a fish's body, with more or less straight sides.
Barbel A threadlike structure or "whisker" on the head near the mouth.
Basibranchial Teeth Very small teeth on the basilbranchial plate near the base of the tongue.
Branchiostegal Rays Slender bones in the gill membrane, located below the gill cover at the edge of the gill opening.
Canine Teeth Long pointed teeth; they may be straight or curved, and are often fanglike.
Cardiform Teeth Short pointed teeth in multiple rows.
Catadromous Any fish taht migrates from freshwater to the sea for purposes of spawning, as does the American eel. Catadromous is the opposite of anadromous.
Caudal Toward the tail, or pertaining to the tail.
Caudal Fin The tail or tail fin.
Caudal Peduncle That portion of a fish's body immediately preceding the tail, from the base of the anal fin to the base of the caudal fin.
Circulus (pl. circuli) One of a series of concentric ridges that form rings or arcs on the scales of fishes.
Conical Teeth Short pointed teeth.
Ctenoid Scales Scales with pointed projections (teeth or ctenii) on their posterior margin. In some species the ctenii are microscopic; in others they are pronounced and make the fish feel rough to the touch.
Cycloid Scales Smooth scales with an evenly curved posterior margin.
Dorsal Fin The prominent fin on the back. Some species have 2 or more dorsal fins; most cods, for example, have 3 dorsal fins.
Emarginate A tail fin that is concavely curved but not definitely forked (such as the tails of trouts).
Falcate A tail fin shaped like a sickle (such as the tails of jacks); it is deeply concave, with the middle rays much shorter than the anterior or posterior rays.
Frenum The connecting membrane that holds the upper jaw to the snout.
Ganoid Scales Hard, diamond-shaped scales that occur on the more primitive bony fishes such as the gars and on the upturned lobe of the tail in sturgeons and paddlefish.
Gas Bladder A membranous structure occurring under the kidney in most but not all fishes, also known as the swim or air bladder. The gas bladder acts as a flotation organ to adjust the weight of the fish to equalize water displacement so that the fish neither rises nor sinks. It can also serve as a noise-producing organ and acts as a resonator in hearing. Species that do not possess or have only a rudimentary gas bladder, such as the darters or Atlantic mackerel, sink to the bottom if they stop swimming.
Gonads The reproductive organs of either sex.
Heterocercal A tail having a long upper lobe and a shorter lower lobe. The vertebral column extends into the upper lobe. It is typical of sharks.
Homocercal A symmetrical tail with lobes of equal length. The vertebral column ends at the base of the tail and does not extend into the upper lobe. It is typical of sunfishes.
Incisiform Teeth Flattened chisellike teeth.
Isthmus The throat or fleshy area that separates the gill chanbers.
Keel Scales or tissue that form a sharp edge.
Lateral Line Pored scales extending from the head along the side of the body usually to the base of the caudal fin. Some species do not have a lateral line while in others it may be incomplete or branched or may extend into the caudal fin.
Line A very narrow marking on a fish's body; it may be oriented in any direction.
Lunate A tail that is sickle in shape but not as deeply concave as falcate. It is typical of the tunas.
Mandible The lower jaw.
Maxillary Pertaining to or denoting the upper jaw.
Molariform Teeth Broad, low, flattened teeth used for grining and crushing.
Nape The back of the "neck" from the occiput to the first ray of the dorsal fin.
Nares The nostrils.
Nuchal Pertaining to the nape.
Nuchal Band A band of color transversing the nape.
Occiput The back of the head.
Ocellus A usually round marking on a fish's body surrounded by a halo of a lighter color.
Omnivorous Eating both plant and animal foods.
Opercle The large posterior bone of the head covering the gills; also called gill cover or operculum.
Orbit The bony eye socket.
Palatines Paired bones on each side of the roof of the mouth.
Palatine Teeth Teeth occurring on the palatine bones.
Parr Specifically, a juvenile trout or salmon distinguished by dark vertical blotches or aprr marks on its side.
Pectoral Fins The anterior paired fins behind the gill openings.
Pelagic A fish that spends most of its life close to the surface of the sea, such as the tunas. Fish of pelagic habits are opposed to demersal species, which live close to the bottom, such as the cods.
Pelvic Fins The posterior paired fins on the ventral surface of the body.
pH A measure of acidity or alkalinity based on a 1 - 14 scale. Neutral is 7; below 7 acidity increases, and above 7 alkalinity increases.
Pharynx The alimentary canal between the mouth and the esophagus.
Placoid Scales These are dermal denticles, resembling a tooth in structure, which form the rough skin covering of most sharks, skates, and rays.
Plankton Animals that float and drift passively in the water of the seas, lakes, and rivers as distinct from animals that are attached to, or crawling on the bottom. Plankton are mostly of microscopic size and have a large surface area in relation to their weight. Many crustaceans, some mollusks, a few worms, a variety of small larvae, and minute plants (phytoplankton) compose a plankton population.
Preopercle The anterior bone of the gill cover in front of the opercle, behind and below the eye.
Pyloric Caeca Dead-end pouchlike projections attached to the intestinal tract just ahead of the stomach.
Spine The stiff but sometimes flexible rod that acts as a supporting structure in the fins; it is without cross striations and is unbranched.
Spiracle An opening on the posterior portion of the head, above and behind the eye.
Spot A round or nearly round marking on a fish's body.
Striated Marked with narrow lines or grooves that are usually parallel.
Stripe A horizontal marking on a fish's body.
Subterminal Mouth A mouth that opens ventrally with the lower jaw closing within the upper jaw.
Terete A cylindrical and tapering body with a circular cross section.
Thoracic Pertaining to the chest or thorax.
Tooth Count In identifying minnows, the number and arrangement of the pharyngeal teeth is a diagnostic character. A formula of 5 - 4, for example, means that there is a single row of 5 teeth on the left arch and 4 on the right arch. A formula of 2, 4 - 4, 2 means there are 2 teeth in the left outer row, 4 teeth in the left inner row, 4 teeth in the right inner row, and 2 teeth in the right outer row. This identification requires careful dissection and is difficult for anyone except an ichthyologist.
Truncate A tail having a vertical and straight posterior margin, such as the tails of groupers.
Tubercles Hornlike projections on the skin which develop on some species during the breeding season, notably many minnows; sometimes called pearl organs.
Vermiculations Wormlike color patterns on the skin, which occur on species such as the brook trout and Spanish mackerel.
Ventral Relating to the abdomen or underside of the fish; opposed to dorsal.
Villiform Teeth Small conical teeth in several rows.
Vomer A median bone at the front of the roof of the mouth.
Year Class The fishes spawned in any one calendar year.
Zooplankton Protozoa and other animal microorganisms living unattached in water. These include small crustacea such as daphnia and cyclops.