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Adipose fin. Small, fleshy fin on the back and near the tail of certain fishes.
Adipose fin

Anadromous fish. Fishes living in the ocean (or other large waterway) but which enter fresh water (in the case of lake-dwellers, smaller) streams to spawn.

Anal fin. Single fin on underside of fish between the vent and tail.

Axillary process. Elongated, membranous material occurring at base of pectoral and pelvic fins.

Barbel. Slender, fleshy projection on the head, usually around the mouth; includes tactile (sensitive to touch) organ.

Binocular, monocular vision. Binocular vision means using two eyes. Monocular vision means using only one eye.

Bony plates. Hard, heavy scales.

Brackish. Somewhat salty.

Branchiostegal rays. Small, slender bones that support the gill membranes.

Candidate. Species that may become threatened or endangered.

Catadromous fish. Fishes living in freshwater streams, but which return to the ocean to spawn.

Caudal fin. Tail of a fish.

Ctenoid. Having a toothed (rough) margin (refers to fish scales).

Cycloid. Smooth, with circular or concentric lines of growth (refers to fish scales).

Diatoms. A kind of algae.

Diurnal, nocturnal feeders. Diurnal feeders eat during the day. Nocturnal feeders eat at night.

Dorsal fin. Fin on the back of a fish: may be divided into parts on some species.

Endangered. Might become extinct or extirpated.

Eutrophy. Material in the water, mostly on the bottom, that is rich in nutrients.

Extirpated. Cannot be found in Pennsylvania anymore, but might be found in other places.

Estuary. Mouth of a river where its fresh water mixes with salt water and is affected by tides.

Extinct. No living species. The animal doesn’t exist anywhere anymore.

Fauna. Animals living in a particular area.

Fingerling. A young fish, older than fry but usually not more than one year old.

Fry. Newly hatched fish; usually in various stages of progression: sac fry, swim-up fry, fry, fingerling. Length of stages may vary with species.

Gill arches. Bony structures that give internal support to the gills; also called pharyngeal arches.

Gills. Organs through which oxygen is absorbed from the water; protected by gill cover called opercle or operculum.

Hybrid. Offspring resulting from breeding between parents of two different species.

Invertebrates. Animals without a spinal column (backbone).

Kype. Hooked jaw acquired by trout and salmon, especially at spawning time; it is comprised of cartilage.

Lamellae. Membranes of a fish’s gills that look like teeth on a comb supported by bony arches.

Lateral line. Line of scales running lengthwise on each side of a fish with openings or pores connected to a sensory canal.

Maxillary. Hindmost corner bones of the upper jaw.

Migrate. Move periodically from one area to another to live, spawn or feed.

Nares. Nasal cavities, nostrils.

Olfactory. Of or relating to the sense of smell.

Opercle or Operculum. Gill cover.

Otolith. Ear bone.

Pearl organs. Horny structures protruding from the head or scales; developed during the breeding season.
Pearl organs illustration

Pectoral fin. Uppermost fins on either side of the body and usually just behind the gill.
Pectoral fin illustration

Pelagic. Of or relating to open water or the open sea; not near-shore.

Pelvic fin. Fins on either side of the body, below and often behind the pectoral fins.

Pharyngeal arches. See gill arches.

Pharyngeal teeth. Teeth-like structures found in the throat, attached to the gill arches. See gill arches.

Protractile. To be thrust outward or extended.

Ray. Bony structure supporting the membranes of the fin.

Soft ray. Flexible, jointed ray supporting a fin.
Soft Ray

Scute. An external bony or horny plate, or large scale.

Spine. Sharp, pointed structure.
Fish spine illustration

Spiny ray. Flexible, jointed ray supporting a fin.
Spiny ray illustration

Swim-up fry. Newly hatched fry in early stage of swimming up for feed after absorption of egg or yolk sac is complete.

Threatened. Might become endangered.

Tooth patch. Group of small teeth located on the base of the tongue.

Triploid. Having a chromosome number three times the monoploid number.

Tubercle. A small, knobby nodule on a fish’s head, body or fins (see pearl organs).

Turbid. Opaque; muddied; caused by suspended matter, usually sediment or the result of rain runoff.

Vertebrae. Spinal column; the backbone.

Vertebrate. Animal having a spinal column or backbone.

Vermiculation. Irregular, wavy, worm-like lines.

Zooplankton. Very small animal life in water.
Zooplankton illustration