Frequently Asked Questions
The most-asked questions about fish.
What exactly is a fish?
A fish is any cold-blooded, gill-breathing vertebrate (or close relative) that lives in water and propels itself with fins. They span an enormous range of sizes and shapes, from millimetre-scale killifishes to the 12-metre whale shark, making them the most diverse vertebrate group on the planet.
Who are the 'main characters' a newcomer should know?
The household names include the great white shark, the clownfish, the deep-sea anglerfish, and the Pacific salmon. For the legendary 'living fossil' slot, the coelacanth holds the crown, having been found alive in 1938 after 66 million years presumed extinct.
Where should a newcomer start exploring?
Begin with the three major lineages—bony fish, cartilaginous fish (sharks and rays), and the ancient jawless groups like lampreys and hagfish. Picking a single habitat, such as a coral reef or the hadal zone, then gives you a natural thread to follow through thousands of species.
How many species of fish exist?
Roughly 35,000 species have been formally described, and taxonomists add new ones almost every year. That total dwarfs mammals, birds, and reptiles combined, making fish the largest vertebrate group by a wide margin.
What is the biggest fish in the world?
The whale shark, which can exceed 12 metres in length, is the largest living fish. Despite its imposing size it is a gentle plankton filter-feeder, earning it the nickname 'gentle giant of the sea.'
What is the oldest fish still swimming today?
The coelacanth, a lobe-finned fish whose body plan has changed very little since the Devonian, was rediscovered alive off South Africa's coast in 1938. Its survival is one of the most celebrated 'living fossil' stories in all of biology.
Do fish actually feel pain?
Two decades of research confirm that fish possess nociceptors and can experience prolonged, stress-related pain rather than a simple reflex flinch. This finding has reshaped both laboratory protocols and the welfare standards of the aquarium hobby.
What separates a true fish from other aquatic animals?
True fish breathe through gills, have fins, and lack limbs with distinct digits. That criterion excludes dolphins, sea turtles, and octopuses, which are frequently mislabelled as 'fish' in casual conversation.
What is a standout 'moment' in fish evolutionary history?
Around 375 million years ago, lobe-finned fish such as Tiktaalik developed limb-like structures and began hauling themselves onto land, launching the lineage that would become every tetrapod. It remains the single most dramatic fish-to-land transition in the fossil record.
Why do fans find fish so endlessly fascinating?
Their staggering variety of shapes, colours, and behaviours—from bioluminescent deep-sea hunters to mirror-bright reef dwellers—gives every observer a different 'main character' to root for. Layer in the sheer mystery of unexplored ocean depths, and fish remain an inexhaustible source of wonder.