5 Fascinating Facts About Fish

A fish is an aquatic creature with a backbone, fins, and a two-chambered heart. One well-known fact about fish is that they breathe oxygen through their gills, unlike terrestrial animals that use their mouths or nostrils to inhale air.

But fish offer so much more than just their gills! For instance, cleaner fish live on the ocean's floor, removing parasites from other species' skin. And flying fish, resembling aquatic birds, boast wing-like fins.

Fish vary greatly, from minuscule beings small enough to rest on a fingernail to massive creatures as large as cabin cruisers. They can sleep with their eyes wide open, taste without using their mouths, and float without casting any shadow. Let’s dive into even more exciting fish facts.

The Most Prevalent Fish in the World Is One We Rarely Encounter

If you're imagining a tuna, flounder, or goldfish, think again. The most widespread fish species on Earth is one that humans almost never come across.

Why is that? Primarily because it's small and cleverly disguised. But more importantly, this fish inhabits depths ranging from 100 to 250 fathoms beneath the ocean's surface. Meet the bristlemouth, a species in the genus Cyclothone (which includes another 13 species).

Bristlemouths are unassuming, plain creatures with short bodies and tiny eyes, mostly made up of their mouth and fins. In terms of size, they're quite modest, with most species growing to no more than 3 inches (7.6 cm) long.

However, the bristlemouth possesses a remarkable feature: two rows of photophores, or light-producing organs, on its belly. These help it avoid casting a shadow that could be detected by predators. Among its predators are shrimp, which gives you an idea of just how tiny this fish is.

The Largest Fish Could Be the Most Gentle

Many fish appear far more menacing than they actually are.

The giant of the fish world, the whale shark (Rhincodon typus), resides in semitropical and warm temperate waters worldwide.

Whale sharks can grow over 65 feet (19.8 meters) long and weigh almost 40 tons (36.3 metric tonnes). With their immense size, massive flat head, and distinctive polka-dot pattern, whale sharks might remind you of the creature from Roy Scheider's worst nightmare.

In truth, whale sharks are mostly harmless. They're so gentle that they've been known to let swimmers hitch rides on their backs. As filter feeders, they consume tiny plankton, small fish, crustaceans, and squid instead of biting prey.

Whale sharks can live up to 70 years, unless they fall victim to humans who harpoon them and turn them into fish meal.

The Smallest Fish Is a Male

The title of the world's smallest fish remains a subject of debate. In 2006, the respected UK scientific journal, the Royal Society, published a study on a minuscule fish from the genus Paedocypris, found in Sumatran swamps and measuring just 7.8 millimeters, or about a third of an inch in length.

Not long after, other researchers pointed to an even smaller fish that had already been recorded in scientific literature: an Australian specimen of the stout infantfish (Schlindleria brevipinguis), measuring 7.0 millimeters.

However, the smallest fish is actually a male anglerfish (Photocorynus spiniceps) discovered in the Philippines, which grows to only 6.2 centimeters (around a quarter of an inch) from snout to tail. The male spiniceps is a parasite, living its entire life attached to a much larger female, who does all the work, including swimming and feeding, while he simply holds on.

Fish Possess Taste Buds from Head to Tail

Unlike humans, fish lack 3D vision due to their eyes being positioned on opposite sides of their heads. However, what they miss in binocular vision, they compensate for with highly developed senses of smell and taste, which they depend on to navigate and understand their surroundings.

Certain fish use their sense of smell to locate ideal places to lay their eggs. Migrating salmon, for example, can recognize the scent of their home stream. Sharks, rays, eels, and salmon possess highly sensitive olfactory rosettes (organs that detect scents) that allow them to detect chemical concentrations as low as one part per billion in the surrounding water.

Fish have an equally advanced sense of taste. Many species not only have taste buds on their tongues but also on their fins, faces, and tails. These remarkable creatures can actually taste their food before it even enters their mouths.

Catfish stand out as having the most advanced sense of taste. They are covered from head to tail in taste buds, even their whiskers are equipped with them.

Not All Fish Are Capable of Swimming Backwards

You know the famous saying that Ginger Rogers was more talented than Fred Astaire because she had to do everything he did, but backwards and in high heels? Well, most fish wouldn’t make great dancers, not just because they don’t have feet.

Most of these vertebrate creatures have a body structure that lets them flex their bodies and move their tail fin (caudal fin) to propel themselves through the water. The majority of the force comes from muscles near the tail.

This method works perfectly for swimming forward at high speeds, but even the fastest fish will struggle when it comes to swimming backward.

However, some fish species can pull off the backward movement, using different ways to move. Triggerfish, part of the Balistidae family, for instance, employ a technique known as balistiform swimming. This allows them to move by undulating their dorsal and anal fins, which are positioned to help them move forward and then shift backward through the water.

But these aren’t the only fish capable of moving in both directions! Another example is the electric eel (Electrophorus electricus), which can swiftly move backwards as well. It achieves this agility through a method of locomotion known as gymnotiform swimming, where it undulates its long body and flaps its anal fins to propel itself.