Interesting facts about bony fish

A fascinating group of fish found in waters worldwide are called bony fish. Unlike cartilaginous fish, such as sharks and rays, they comprise the majority of fish species and are distinguished by having hard skeletons composed of bone. However, these animals are far more complex than their skeletons.

The remarkable ways in which bony fish have evolved to suit various environments, including their distinct breathing and swimming patterns, never cease to astound scientists and enthusiasts of the natural world. While some species are small and colorful, others have the capacity to grow enormous and strong.

The world of bony fish is full of surprises, whether you’re drawn to the mysteries of the deep sea or simply want to know more about the fish you see at your neighborhood aquarium. Now let’s explore some of these amazing creatures’ most fascinating facts.

Bony fish require a lot of energy to live

To obtain enough energy to meet their daily physical needs, fish must breathe and eat. Swimming, finding food and a mate, and avoiding predators take up a large portion of the energy. Bony fish have evolved a unique swim bladder—a gas-filled chamber—to conserve energy. Gases enter the swim bladder of the majority of contemporary fish directly from the circulatory system. The fish is kept buoyant and weightless in the water column by this bladder. With the help of this system, fish can spend several hours at the same water level without using up too much of their precious energy.

Bony fish have specialized gill chambers

All bony fish, with very few exceptions, need a steady supply of oxygen to breathe. Fresh and salt water both contain freely available dissolved oxygen, which fish remove by passing water through specialized gill chambers that are densely packed with blood vessels. Oxygen enters the bloodstream’s red hemoglobin cells through thin membranes as water travels over the gills’ intricately patterned surface.

Their sizes vary from a few centimeters to several meters

Bony fish come in thousands of species, with lengths of only a few centimeters. The critically endangered pygmy goby (Pandaka pygmaea) is one of the smallest. Adult females are only around 9 mm long, while adult males can grow to be 15 mm long.

Some animals have the ability to grow to enormous sizes—much larger than a human. The oarfish, or Regalecus glesne, is the longest bony fish, reaching a maximum length of 11 meters. The common ocean sunfish (Mola mola), which inhabits warm and temperate waters worldwide, is one of the heaviest bony fish. The large sunfish has a maximum length of 3.3 meters and a weight of 2,300 kg.

The family Acipenseridae includes many large-growing sturgeons. The beluga (Huso Huso), which inhabits the Black, Caspian, and Adriatic Seas, is the biggest of these. It has a maximum length of 5 meters and a weight of 2000 kg. Makaira indica, the black marlin, can reach lengths of 4.7 meters and a weight of 750 kg. The European catfish, or Silurus glanis, has a maximum length of 5 meters and a weight of roughly 300 kg.

Bony fishes are the most numerous of all fish species

With over 28,000 species, the group of bony fishes (Osteichthyes) is the most diverse group of vertebrates in science. Among these species are 50 extinct or anachronistic species that dominated the fish fauna millions of years ago. Roughly 96% of all fish species are included in this. Many more have probably still to be identified, including some deep-sea species.

Fish classified as bony are difficult to classify. How best to divide them is still up for debate. Currently, researchers have identified over 500 distinct bony fish families and recognize Actinopterygii, Crossopterygii, and Dipnoi as the three subclasses.

Ray-finned fishes are the largest class of bony fishes

Several other small groups of fish, including the Polypteridae (bichirs), Acipenseridae (sturgeons), Polyodontidae (copepods), and Lepisosteidae (pikes), belong to the class Actinopterygii. Currently, over 20,000 species of ray-finned fish have been identified, inhabiting a variety of aquatic, marine, and terrestrial habitats. All ray-finned fishes have fins supported by bony structures known as rays, despite the large variations in size, appearance, and structure among these species. It is believed that bony insects originated from early ray-finned fishes that are related to extinct species that still exist today.

With a length of just 12 mm, the Philippine goby (Pandaka pygmaea) is the smallest known ray-finned fish. With a length of five meters, the largest is the arapamia (Arapamia gigas) found in the Amazon rivers.

Coleopterygian fishes evolved 400 million years ago

A few primitive bony fishes still occur in nature and for taxonomic purposes they are grouped together in the subclass Crossopterygii. One of these is the coelacanth (Latimera chalumnae), a large blue-gray fish that can grow up to two meters long. Many of its features are similar to fossil species, the most notable of which is the arrangement of the fins. The rays of the second dorsal fin, anal fin, and paired fins rest on a muscular, scale-covered lobe, and the powerful caudal fin has a symmetrical appearance. Scientists previously thought that this entire subclass of fish was extinct. But in 1938, a living coelacanth (Latimeria chalumnae) was discovered off the coast of Southeast Africa. Several specimens have been collected since then. Early lobe-finned fish are thought to have given rise to amphibians in the Devonian period, about 360-400 million years ago.

Lungfish survive droughts

The lungfish found in Africa, Australia, and South America are among the other peculiar species that belong to the same group. These fish are the only surviving members of a large group that was present on Earth approximately 350 million years ago. A continuous median fin is formed in some of them by the fusion of the dorsal, anal, and caudal fins. A fused upper jaw with the braincase, fused teeth, and an air-breathing organ that opens into the esophagus are other characteristics shared by members of the subclass Dipnoi. Their pectoral and pelvic fins are tubular and long.

While some species have evolved gills to breathe in water, others come to the surface to take in oxygen. African and South American species bury themselves deeply in the mud at the bottom of lakes and swamps and coat themselves in a thick layer of mucus during dry spells. The fish can withstand the winter’s drought because the mucus gives them a protective layer when it dries. The mucus thins and the fish swims out once more when the rains come back.

Fish fossils have been found dating back 550 million years

The earliest fish date back to the Cambrian period, about 550 million years ago. These jawless fish lived relatively unchanged for the next 100 million years. The Devonian period, about 360-400 million years ago, is known as the "Age of Fishes" because of the abundance and diversity of fish that appeared during this period. In the Devonian, they began to develop jaws and paired fins. They had tough skin, often reinforced with massive scales to help them withstand periods of adverse weather or avoid over-predation. All four living classes of fish and three subclasses of Osteichthyes had appeared by the middle of the Devonian. Many species of fish that lived during the Devonian are now extinct. However, bony fish continued to evolve after the Devonian. Most modern bony fish orders probably arose in the Triassic period, about 200 million years ago.

Bony fish are the dominant vertebrates in the oceans and freshwater systems

Unlike cartilaginous fish, which are restricted to saltwater, bone fish can be found worldwide in both fresh and saltwater environments. From shallow to deep water, marine bony fish can be found in all tropical, temperate, and polar seas and oceans. While some species inhabit lakes that are as high as 5 km above sea level, others live at depths of up to 11 km.

They have adapted to live in a range of environments, including lakes, ponds, rivers, streams, kelp forests, and stony beaches. Approximately 13,000 species, or 58% of all bony fish species, are found in marine environments. About 42% of bony fish species (more than 9,000 species) are freshwater fish, despite freshwater making up only 0.01% of all water on Earth.

David Clode took this picture.

Bony fish can withstand both high and low temperatures. The Antarctic icefish, which lives in water so cold that antifreeze proteins (glycoprotein molecules) are constantly circulating throughout her body to keep her from freezing, is a striking example of their adaptation to extreme conditions. In California, there are some desert minnows (Cyprinodon macularius) that inhabit 45°C hot springs.

Most bony fish have small home ranges

Certain species may migrate in response to environmental factors such as temperature fluctuations, reproduction, ecological cycles, and food availability. The majority of tuna species migrate. Over 8,500 kilometers separate the albacore (Thunnus alalunga) migration from California to the coast of Japan across the Pacific Ocean. Albacore’s tagging studies show that they cover 26 km on average each day.

Certain bony fish migrate between freshwater and marine environments because they are diadromous. Others are freshwater animals that migrate downstream to the ocean to spawn; this is known as catadromy. The Anguillidae family of freshwater eels migrates from marine environments to freshwater rivers to live. Adromous fish migrate to freshwater habitats to spawn, but they spend the majority of their lives in the ocean. In order to spawn, ockeye salmon (Oncorhynchus nerka) must travel more than 3,600 kilometers upriver.

Bony fish have a fusiform shape

Although bonny fish have a wide range of body forms, fish with a "typical" body shape are generally cylindrical and tapered at both ends. When moving, the fusiform shape produces less drag than other body shapes.

Because of their surroundings, certain species have altered the typical fusiform body shape. Bony fish that reside in areas with lots of cover or on coral reefs frequently have bodies that are laterally compressed, or flattened from side to side. For instance, butterfly fish (family Chaetodontidae) typically have this shape. Fish that live at the bottom typically have a depressed shape, which is flattened from top to bottom. Sea bats (family Ogcocephalidae) and angler geese (family Lophidae) are two examples. Bony fish, like the muraenidae family’s moray eel, also have an elongated eel-like body shape.

Most species have pigmentation

The majority of pigment is found in cells known as chromatophores. The majority of fish have chromatophores that can expand and contract to change color. Iridocytes are light-reflecting cells with a fast rate of color change. Fish often appear different underwater than they do above because different light wavelengths are absorbed at different depths. Certain fish are pigmentless, like the glass catfish (Kryptopterus bicirrhis).

The coloration provides good camouflage for the fish. In most species, the dorsal surface is darker than the ventral surface. When light comes from above, the animal appears invisible. The shadowed dorsal side of the fish blends in with the dark ocean depths or the seabed when viewed from above. The ventral side blends in with the lighter sea surface when viewed from below. These fish are harder for predators and prey to detect. Some fish are colored to blend in with their surroundings. Many bottom-dwelling fishes are colored to match their substrate, and even change color when moving to a new location. The northern pike (Esox lucius) colors harmoniously with the weed beds where it lies in wait for prey.

Fish with destructive coloring are common. Their pattern and color defy the fish’s outline and contrast with its body’s shape. Additionally, some fish have an eye patch that can deceive a predator into attacking in the incorrect direction, allowing the fish to get away. During the breeding season, some species change their color to attract potential mates.

As they mature, bony fishes can occasionally change color. For instance, juvenile garibaldi (Hypsypops rubicundus) are bright orange as adults, but juveniles are dark orange with bright blue spots. Certain species have the ability to change their sex, which results in a color change. The majority of wrasse species (family Labridae) and angelfish (family Pomacanthidae) are two examples. Temporary color changes are possible. Fish, for instance, frequently change color when startled. Certain fish that live at the bottom instantly change color to blend in with their surroundings.

Certain species possess luciferins that, when oxidized, release light. Other fish use bacteria that reside inside them or on their scales to produce light. Depending on the species, bioluminescence can serve as a fish’s "headlights" to help it see in the dark, attract mates, fend off or confuse predators, or draw in prey.

The digestive system of bony fish is suitable for processing different types of food

Bony fish have an esophagus that is both short and expandable, allowing them to swallow large objects. Muscles line the inside of the esophageal walls. The majority of animals have a stomach, which is a muscular tube with a U or V shape. Food is broken down by substances secreted by the stomach glands, making it ready for digestion. Many bony fish have blind sacs called pyloric canals at the end of their stomachs. These modifications aim to expand the intestine’s surface area.

In the intestine, food is absorbed primarily. Bony fish have a wide range of intestinal lengths. Species that consume plants usually have long, twisted intestines. The intestine of a predatory bony fish is shorter.

Bony fish have a wide range of dietary preferences

They may be detritivores, which eats decaying plants and animals, herbivores, carnivores, or omnivores. Generally speaking, bony fish can consume any size of plant or animal, ranging from tiny plankton to massive marine creatures. They frequently eat fish, amphibians, crustaceans, mussels, mollusks, squid, annelids, insects, and other sea snails.

The relationship between a bony fish’s size, metabolic rate, and environmental temperature and how much food it consumes is clear. Generally speaking, smaller members of the same species have higher metabolic rates than larger members. Generally speaking, fish in warm water need more food than fish in cold water of the same size. Certain bony fish can survive for a very long time without food. It is possible for freshwater eels to go over a year without eating!

As the largest group of vertebrates on Earth, bony fish are known for their unusual bone skeletons, capacity to breathe through gills, and ability to thrive in a variety of habitats, including freshwater rivers and deep oceans. These fish play a vital role in the world’s ecosystems because of their extreme diversity, with species exhibiting incredible sizes, colors, and behaviors.

Most bony fish detect prey by sound

Their ears are closed off from the outside. The ears receive sound waves after passing through soft tissue. The upper frequency limit, bandwidth, and hearing sensitivity of bony fish species vary greatly. Most bony fish species most likely have a sensitivity of about 20 Hz.

The swim bladder is an adaptation of certain species to higher frequencies of sound. Sometimes the swim bladder is affixed to the ear, functioning as an amplification device to enhance auditory perception. Some animals, like goldfish (Carassius auratus), have a network of tiny bones that join the ear and swim bladder. With a peak sensitivity of roughly 400 Hz, goldfish can hear frequencies between 5 and 2,000 Hz.

Image courtesy of Aquascaper Artist

The American shad (Alosa sapidissima) and some related species have been found to be able to hear sounds between 200 and 180,000 Hz, according to recent research. Scientists hypothesize that dolphins’ echolocation, which usually produces clicks at roughly 100,000 Hz, is avoided by their ultrasonic hearing.

The lateral line of bony fish senses vibrations

The lateral line system consists of a network of canals filled with fluid that run along the sides of the body and just below the head. Through microscopic pores that resemble hairs, the canals that house the sensory cells are exposed to the surrounding water. These hair-like projections are moved by water movement, which can be attributed to vibrations, currents, or turbulence, and this movement activates the sensory cells. These are mainly intended for distance perception, low-frequency vibration detection, and directed water flow.

The eyes of bony fish have different structural adaptations

Bony fish have rods and cones in their eyes. Most likely, they can see color. Certain light intensities and wavelengths are specific to visual cells. Large eyes enable deep-sea fish to take in as much light as possible in the dark. Fish from shallow waters typically have smaller eyes. Certain species, like eels, have pupils that dilate and constrict in response to changes in lighting. But in the majority of species, the pupils are unable to dilate or contract. Large lenses on bony fish enable them to maximize the amount of light that they can see.

Certain bony fish species have the capacity for highly developed vision. Excellent visual acuity is possessed by the goldfish (Carassius auratus) up to a distance of 4.8 meters. Some animals have no eyes at all. The Amblyopsidae family of blind cave fish lacks visual perception.

Sexual maturity is affected by age, sex, and size

Smaller species typically start reproducing earlier in life than larger ones. Certain bony fish exhibit sexual maturity from birth. Micrometrus minimus, the male dwarf bass, can spawn right away after birth. The majority of bony fish reach sexual maturity at five years of age. A few reach sexual maturity between the ages of 10 and 15.

Sperm and eggs develop in distinct male and female individuals in the majority of species. In certain species, an individual produces both sperm and eggs, making them hermaphrodites. Hermaphrodites change sexes during their lifetime, having been born as one sex. Certain species have the ability to fertilize themselves.

Numerous elements, such as variations in the amount of sunlight received, the presence of the opposite sex, currents, tides, moon phases, and the accessibility of spawning grounds, can have an impact on bony fish reproduction. Usually, reproduction follows a cycle. Cycles might extend from four weeks to several years. Certain species continually procreate in the spring and summer. Others are limited to one reproduction per lifetime.

Fertilization and embryonic development vary by species

There are bony fish that lay eggs and "spread" them. A few eggs float in the water column. Drops of oil make them float. On the ocean floor, others grow older. Certain bony fish eggs have tendrils or are sticky, allowing them to get tangled in plants and other organic and inorganic materials in their surroundings. Sometimes parents will shield their eggs from harm until the embryos grow and the offspring are able to swim.

The developing embryo of an oviparous bony fish feeds on the yolk sac that forms prior to fertilization. Oviparous fish lay their eggs in their mouths, skin, fins, or gills. Typically, the eggs are spherical. The egg is shielded by a thin membrane. The majority of them range in diameter from 0.4 to 3.0 mm.

In fish that are viviparous, the female stores the fertilized eggs in the uterus or ovary, and the developing embryo receives nourishment from the mother. From hatched embryos, fish larvae grow. In many species, the larvae exhibit distinct behavior and appearance from the adults during this transitional stage. They consume plankton, bacteria, or organic waste as they are developing.

Different species have different gestation periods, ranging from a few days to several months. The rate of embryo development varies depending on the water temperature within a given species. The odds of one egg maturing and reproducing are inversely correlated with the number of offspring. An average ocean sunfish can lay over 28 million eggs in a single season by "scattering" unfertilized eggs!

Fact	Description
Bony Skeleton	Bony fish have a skeleton made of bone, unlike cartilaginous fish like sharks.
Gills for Breathing	They breathe by passing water over their gills, which extract oxygen from it.
Swim Bladder	Most bony fish have a swim bladder, which helps them control buoyancy in the water.
Scales	Their bodies are covered in scales that help protect them and reduce friction while swimming.
Wide Range of Species	Bony fish make up the largest class of vertebrates, with over 28,000 species.

Bony fish are incredibly fascinating animals that provide insight into the amazing variety of life found in our rivers, lakes, and oceans. They are distinguished from other fish by their distinct skeleton structure, which gives them flexibility and strength in the water.

Bony fish are a marvel of the inventiveness of nature, from their brilliant colors and amazing adaptations to their amazing ability to control buoyancy with a swim bladder. Numerous species are also essential to the balance and biodiversity of their ecosystems.

The next time you see a bony fish, in the wild or in an aquarium, you’ll recognize the special characteristics that set them apart. Both scientists and fish enthusiasts are still fascinated by their evolution and characteristics.

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