Ampullae of Lorenzini: Electroreceptive organ covering the head and snout area of Chondrichthyes (sharks, skates, rays, and chimaeras), as well as several species of primitive bony fish. Used for detecting electrical fields of other aquatic organisms.

Anal Fin: Fin on median line behind the anus/vent.

Anterior: Directionally toward the head.

Anus: Terminal opening of the alimentary (digestive) canal. Also called a ‘vent’.

Benthos: The seafloor.

Buccal Pumping: A mechanism in slow moving or sedentary fish used to move water over their gills in one direction, anterior to posterior, to facilitate gas exchange. Water moves into the expanding buccal chamber through the mouth while the gills are closed, and is then pushed over the gills and through the gill slit or operculum while the mouth is closed and the buccal chamber contracts.

Catadromous: A from of Diadromy, in which larvae are born in the marine environment, migrate to freshwater for their adult life, and migrate back to the marine environment to spawn.

Caudal Fin: Tail fin.

Caudal Peduncle: Region connecting the dorsal and anal fin insertion points to the base of the caudal fin.

Cephalic lobes: Used for feeding and communication, and contain electrosensory pores. Derived from anterior pelvic fins. Present in several pelagic species of Batoid rays. Read more.

Cheek: Region of the head ventral and posterior to the fish’s eye.

Claspers: External intromittent copulatory organs of male Chondrichthyes (sharks, skates, rays, and chimaeras), derived from the pelvic girdle. Also called ‘mixopterygia’.

Coronet: ‘Crown-like’ spine seen dorsally on head of Seahorses. Thought to be used to amplify clicking noises used in communication and to attract mates. Coronets are unique to each individual, as a fingerprint is to a human.

Countershading: Camouflage technique seen in many fish species. The dorsal part of the fish is dark in color so that when seen from above, the fish blends in with the bottom environment. The ventral part of the fish is light in color so that when seen from below, the fish blends in with the light entering the water column from above.

Diadromy: Fish species who migrate between freshwater and marine environments for a portion of their lifecycle. Includes Anadromy (e.g. Salmon), Catadromy (e.g. American Eel), and Amphidromy (e.g. Gobie spp.).

Dispersal: Movement or spread of larvae away from where they were hatched.

Diurnal Vertical Migration: Vertical movement within the water column concurrent with a 24 hour cycle. Directional movement is dependent on the time of day, with most organisms living beneath the photic zone during the day to avoid predation, and living nearer to the surface of the water column from dust to dawn to follow their food source.

Dorsal: The top/upper part of the body.

Dorsal Fin: Fin(s) on the top of the body.

Ecological Niche: An organisms role in a broader complex community. This includes the environment they live in and how they utilize it’s resources, as well as their relationship with other organisms in their environment.

Elver: The life cycle in eels when they are transitioning from the marine environment to freshwater and starting to run up rivers. This is also the stage when pigmentation appears.

Environmental Cues: An outside stimulus that triggers a behavior or physiological response in fish, e.g. salinity, water temperature, light, the lunar cycle, etc.

Euryhaline: A fish that is able to maintain its osmoregularity when moving between freshwater and saltwater environments.

Gill Arch: Bony arches where the gills attach.

Gill Filament: Threadlike projections along the posterior edge of the gill arch, facilitating gas exchange.

Gill Raker: Bony or cartilaginous element on the anterior of the gill arch, opposing the gill filaments.

Gill slits: Openings to gills in species which lack an operculum.

Gills: Respiratory organs for extraction of oxygen from water, and for excretion of carbon dioxide, ammonia, and urea.

Juvenile: A fish that has not yet reached sexual maturity.

Labial Fold: A small fold on the lips at each corner of the mouth.

Larva(e): A hatched fish before reaching metamorphoses into a juvenile that does not resemble an adult of the same species. Larval fish species undergo indirect development, as opposed to direct development, where hatched young are born in a juvenile form resembling an adult of the same species.

Lateral Line: Sensory system composed of neuromasts, pores and canals that run throughout the length of a fish’s head and body; used to detect vibrations and water displacement.

Laterally Compressed: A fish that is compressed laterally, often resulting in a deep-bodied shape. The dorsal and anal fin remain medially.

Leptocephalus: A transparent willow shaped larva of several primitive fish spp, e.g. American Eel and Atlantic Tarpon.

Morphology: Form and function of an organism (how an organism looks, and how are it’s features to navigate it’s environment and perform biological and physiological processes).

Nape: Upper region posterior to head.

Nares: Nostrils

Nictitating Membrane: A moveable a ‘third eyelid’. Used to protect the eye when attacking prey or other circumstances where protection is warranted.

Oligotrophic: An aquatic environment with low nutrient availability.

Ontogenetic Vertical Migration: Vertical movement within the water column that is determined by the stage of growth of the organism (as opposed to a diurnal cycle).

Operculum: Plate-like structure covering the gills.

Oviparous: Laying eggs in an external environment (outside of the female fish’s body, however, eggs can be fertilized internally or externally).

Ovipositor: An egg laying organ in female fish; A tube-like egg duct allowing a female to deposit her eggs outside of her body.

Pectoral Fins: Anterior or or most dorsally located of the paired fins.

Pelvic Fins: Paired fins posterior or ventral to the the pectoral fins.

Planktonic: An organism, “at the whim of the current”, typically drifting with the currents in their environment without the ability to swim against them.

Posterior: Directionally toward the tail.

Precaudal Pit: A small pit on the posterior portion of the caudal peduncle, just anterior of the caudal fin.

Recruitment: When a fish reaches the next stage of development, for example, when a larvae metamorphoses into a juvenile. In Fisheries, recruitment is often used to describe a fish who has grown to legal size to harvest.

Selemparous: Spawning only once. Seen in many Diadromous fish species with long migrations.

Soft Ray: Bony element that supports the fin; bilaterally paired, segmented, and flexible; used in undulatory movements.

Spine: Bony element that supports the fin; unpaired and unsegmented.

Spiracle: Openings posterior to the eyes in Elasmobranchii (sharks, skates, and rays). Used for respiration in some species. In others, gill lamellae in the spiracle oxygenate blood that is utilized by the eyes and brain.

Sub-terminal Mouth Shape: Mouth slightly pointed down, with it’s origin below the end of the snout.

Terminal Mouth Shape: Mouth facing straight forward, with both upper and lower jaws of the same length.

Zooplankton: Microscopic organisms living in the photic zone of the water column.