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Educational Reference

Fish Anatomy Library

Every anatomical structure that makes a fish a fish - explained plainly, cross-referenced to species that showcase each feature. From the swim bladder to the lateral line, gills to otoliths, we cover the parts that matter.

🐟 30 structures 🧬 10 systems

Circulatory Anatomy 1 structure

Heart (Two-Chambered)

The fish heart has only two chambers - one atrium and one ventricle - and pumps deoxygenated blood i...

Digestive Anatomy 3 structures

The largest internal organ in most fish - handling metabolism, detoxification, and (uniquely in shar...

Highly variable feeding structures - from the dagger teeth of piranhas to the fused parrot-beak of p...

Finger-like pouches extending from the intestine just after the stomach - unique to bony fish, they...

Excretory Anatomy 1 structure

The paired osmoregulatory organs of fish - filtering blood, producing urine, and (in some) also serv...

External Anatomy 9 structures

A small fleshy fin between the dorsal fin and tail found in salmonids, catfish, and some tetras - it...

The unpaired fin on the underside just before the tail - a stabiliser that prevents rolling and, in...

The tail fin - the primary propulsive structure that generates thrust and steers the fish.

The fin on top of a fish - stabilizes against rolling, may be used for defense (spines) or communica...

A bony flap covering and protecting the gills, which also pumps water across them by rhythmic muscul...

The paired fins just behind the head - equivalent to front limbs, used for braking, turning, hoverin...

The paired ventral fins - equivalent to hind limbs, used for stability, precise braking, and in some...

Small protective plates covering the skin of most fish - reducing drag, deflecting parasites, and re...

Skin and Mucus Layer

The outer covering of a fish - a living, mucus-secreting barrier that protects against pathogens, re...

Internal Anatomy 1 structure

A gas-filled internal organ that controls buoyancy, allowing fish to hover at a chosen depth without...

Nervous Anatomy 2 structures

Specialised muscle-derived tissue that generates electric fields - used for hunting, defence, naviga...

The central nervous system of a fish - smaller than a mammals relative to body size but capable of l...

Reproductive Anatomy 1 structure

A single posterior opening in cartilaginous fish (and some primitive bony fish) that serves both exc...

Respiratory Anatomy 2 structures

Bony or cartilaginous projections on the inner edge of gill arches - filter food from water and prot...

The primary respiratory organs of fish, extracting dissolved oxygen from water flowing across filame...

Sensory Anatomy 8 structures

Ampullae of Lorenzini

Pore-based electroreceptors around the head of sharks, rays, and chimaeras - detecting the electric...

Whisker-like sensory appendages around the mouth of bottom-feeding fish, packed with taste and touch...

The visual organ of fish - built around a spherical lens optimised for underwater refraction, with r...

A sensory canal running along each side of a fish that detects water pressure changes, vibrations, a...

Nostrils (Nares)

Small openings on the snout that lead to olfactory sacs - the fishs sense of smell, often astonishin...

Calcium carbonate stones inside a fishs inner ear that provide balance, orientation, hearing - and r...

Specialised light-producing organs found in bioluminescent fish - used for prey attraction, camoufla...

Weberian Ossicles

Tiny bones connecting the swim bladder to the inner ear in ostariophysan fish - giving them exceptio...

Skeletal Anatomy 2 structures

Fin Rays and Spines

The bony or cartilaginous supports of fish fins - soft rays are flexible and branched, spines are st...

Vertebral Column

The chain of vertebrae that runs from head to tail - the central skeletal element of every vertebrat...