Guest Author - Deborah Watson-Novacek
Ichthyology uses many terms that are unique to the science. This is a glossary of terms used in ichthyology, fisheries, fisheries management and fisheries science.
A
Abundance - a measurement of how many fish are in a given population or a fishing ground.
Actinosts - a series of bones at the base of the pectoral rays.
Acoustic survey - a gathering of information on fish availability and abundance using underwater sound
Adipose fin - a small fleshy fin which lacks fin rays.
Aerial survey - a method of gathering information on surface fish movement and density by visual observation and photography from low-flying aircraft
Aggregation - is a term which can be applied to any grouping of fish
Algal bloom - a rapid excessive growth of algae, generally caused by high nutrient levels, particularly phosphorus. When the algae die, algal blooms can deplete oxygen to the point where fish cannot survive.
Anal fin - the fin on the median line behind the vent
Anadromous - fish that live their adult lives in the ocean but migrate up fresh water rivers to spawn.
Aquaculture - the farming of freshwater and saltwater organisms including molluscs, crustaceans and aquatic plants.
Axillary - pertaining to the axilla or upper angle of the pectoral fin
Axillary process - an enlarged, pointed scale projecting from the insertion of the pectoral or pelvic fin.
B
Bait fish - small fish caught for use as bait to attract large predatory fish.
Barbel - an elongated fleshy projection, usually about the head
Bathypelagic - living at a depth between 1000 m and 4000 m, but well off the bottom. The open ocean or pelagic zone that extends from a depth of 1000 to 4000 meters below the ocean surface.
Benthopelagic - pertaining to fishes that swim just above the seabed at depths below about 200 m (the edge of the continental shelf)
Benthos - aquatic organisms which live on or in the seabed, also known as the benthic zone. Examples are crabs, abalone, corals and sponges.
Billfish - large, predatory fish characterised by their long sword-like bill, such as sailfish, marlin and swordfish.
Biodiversity - the number and variety of organisms found within a fishery.
Biomass - the total weight of a fish species in a given area.
Bony fish - fish that have a bony skeleton and belong to the class osteichthyes. Basically, this is all fish except for sharks, rays, skates, hagfish and lampreys.
Bottom trawling - a fishing method that involves towing trawl nets along the sea floor.
Brackish water - water that has more salinity than fresh water, but not as much as seawater.
Branchial - pertaining to the gills
Branchial aperture - the gill opening
Branchiostegal rays - bony rays supporting the gill membranes behind the lower jaw
Breach - a whale's leap out of the water.
Brood - the collective offspring of a species produced in a particular time span.
Bycatch - bycatch is the harvest of marine life and seabirds during fishing operations when other fish were the target.
C
Carapace - a horny or bony covering encasing the body. The carapace is particularly well developed in lobsters and crabs.
Catadromous - fish that live their adult lives in fresh water lakes or rivers but migrate down rivers to spawn in the sea.
Caudal - pertaining to the tail
Caudal fin - the tail fin
Caudal peduncle - the region of the body between the end of the anal fin and the base of the caudal fin
Cephalopods - animals such as squid and octopus where tentacles converge at the head.
Cetacean - member of the group of marine mammals that includes whales, dolphins and porpoises.
Claspers - the external reproductive organs of male sharks, rays and chimaeras
Cohort - those individuals of a stock born in the same spawning season.
Commercial fishery - An umbrella term covering fisheries resources and the whole process of catching and marketing fish, molluscs and crustaceans. It includes the fishermen and their boats, and all activities and resources involved in harvesting, processing, and selling.
Corselet - a scaly covering behind the pectorals of some fishes
Countershading - body coloration which is dark above and lighter below
Crustaceans - A group of freshwater and saltwater animals having no backbone, with jointed legs and a hard shell made of chitin. Includes crabs, lobsters, crayfish, shrimp and krill.
Cutaneous - pertaining to the skin
Ctenoid - rough-edged scales
Cycloid - smooth-edged scales
D
Dead zone - an area in an ocean or large lake where oxygen levels are extremely low, often due to eutrophication.
Demersal zone - the zone at or near the bottom of a sea or lake.
Demersal fish - fish that live in the demersal zone. Examples are cod, flounder and snapper.
Depletion - reducing the abundance of a fish stock through fishing.
Denticle, denticulate - the placoid scales of cartilaginous fishes
Diatoms - minute planktonic unicellular or colonial algae.
Disc - the flattened head and body of various fishes such as stingrays
Dorsal - pertaining to the back
Dorsum - the upper (dorsal) surface of the head or body
Dorsal fin - the fin on a fish's back
E
Echinoderms - a group of marine animals that includes seastars, sea urchins and sea cucumbers.
Elasmobranch - cartilaginous fish that includes sharks, skates and rays.
Epibenthos - invertebrates that live on top of the seabed, or on the bottom surface of the ocean.
Epipelagic - organisms living in the region between the surface and 200 m depth. Nearly all primary production in the ocean occurs here.
Estuarine - living in estuaries
Estuary - a semi-enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea.
Euryhaline - fish that are tolerant to a wide-range of salinities
Consider this glossary as a "living document." More ichthyological and fisheries terms will be added over time.
