The bony fish or osteichthyans are a large group of animals that, together with chondrichthyans or cartilaginous fish and jawless fish, they form the group we normally call “fish”. These fish evolved from animals called ostracoderms, which are considered the oldest vertebrates.
In this article on our site we talk about the characteristics of bony fish and we will show some examples with images and curiosities. Keep reading!
What are bony fish or osteichthyes?
Bony or osteichthyan fish are gnathostome vertebrates whose skeleton is mainly made up of fully calcified bones and few cartilaginous parts. These fish are known as gnathostome vertebrates because they have the articulated jaws Until then, the few vertebrate animals that existed did not have this characteristic and were agnathic vertebrates, that is, animals with skeleton but without jaw.
The appearance of the articulated jaw was a breakthrough for these animals. By increasing the musculature of the mouth, suction increases, which helps predation. In addition, true teeth or bony teeth and paired fins also appeared, which improve movement.
Differences between bony and cartilaginous fish
Bony fish and cartilaginous fish or chondrichthyans have bony, articulated jaws. The main difference between both groups is that in chondrichthyans the rest of the skeleton is cartilaginous.
Although all these animals breathe through gills (with the exception of lungfish), there are relevant differences between the two groups. The gills have extensions called branchial septa, chondrichthyans do not actively breathe and need to be in constant motion for water to pass through the gills. Bony fish have an active respiration, they can breathe in and out, so there are hardly any gill septa in them.
Another difference between bony and cartilaginous fish is found in the genito-urinary apparatus. In chondrichthyans, all ducts empty into the cloaca to remove waste products. In the case of males, it is also used as a spermiduct (Wolff's duct) and is shared with the excretory duct. In females it never happens, they do not share it, because they have a separate Müllerian duct from the waste one. In osteichthyes, the excretory ducts and spermiduct are not shared in males. In females, there is communication between the Müllerian duct (oviduct) and the ovisac. On the other hand, some species of bony fish have a swim bladder. This is never seen in chondrichthyans.
Both groups have scales but they are different from each other. Chondrichthyan scales are called placoids or dermal denticles and can be modified to form spines at the anterior level of the dorsal fins or stingers connected to poisonous glands. In the scales of the osteichthyes there is an internal bone layer that comes from the shell of the ostracoderms (an extinct class of agnathic fish, considered to be the oldest vertebrates). This layer becomes very thin, forming the scales of teleosts. In addition, there are two types of scales:
- Cycloid scales: with smooth edge.
- Ctenoid scales: with serrated edges.
Classification of bony fishes
The oldest fossil remains found of osteichthyes date back to the Devonian. Osteichthyes are evolutionarily divided into two classes:
Actinopterygia
Actinopterygians are characterized by having skin-covered fins supported by horny rays. Evolutionarily they are divided into chondrosteans, holostems and teleosts.
- Chondrosteos: nowadays they occur in a very reduced form, as is the case of sturgeons and bichires. Chondrosteans are characterized by having a body covered with bony plates and a mainly cartilaginous skeleton.
- Holósteos: within this group of fish, the alligator gar currently survive.
- Teleósteos: they evolved from the holosteos during the Mesozoic, replacing the oldest groups of fishes during the Cretaceous, constituting the vast majority of today's fish.
Sarcopterygians
The sarcopterygians are the most important group in terms of the evolution of terrestrial vertebrates. They are characterized by having lobed and fleshy fins. They are divided into:
- Actinistos: its first fossil records correspond to the Devonian and were replaced towards the end of the Paleozoic by the actinopterygians. These are the closest bony fish to land vertebrates. Their caudal fin is divided into three lobes.
- Dipnoos: These are fish adapted to living in shallow pools and rivers. In addition to gills, they have lungs, so they are lungfish. We found the genera Neoceratodus, Protopterus and Lepidosiren.
Characteristics of bony fishes
So far, we have discussed some of the main characteristics of bony fish or osteichthyes. These animals form a very heterogeneous group, although they share many common characteristics that define them as a group.
As their name indicates, osteichthyes are mainly characterized by having a skeleton made up of calcified parts In addition, their heads fish has two parts. The braincase that protects the brain and the splanchnocranium, which forms the articulated jaw. In this jaw we find two very important bones.
- Quadratus bone: gives rise to the hammer of the middle ear of mammals.
- Articular bone: gives rise to the anvil of the middle ear of mammals.
Another characteristic of bony fish is that their skin is made up of the epidermis, where we find mucous glands, and the dermis. The dermis gives rise to scales. As we saw, these scales come from a thin layer of bone that originated in an ancient group of fish called ostracoderms. In some species, the mucous glands can acquire a toxic protein, becoming poisonous glands.
Some bony fishes, especially those that live at great depths, may possess an organ called a photophore A photophore is an organ that emits light. The organ can be simple or as complex as the human eye, equipped with lenses, shutters, color filters, and reflectors. The light can be produced by the animal's own metabolic reactions or associated with symbiotic bacteria within the photophore. The character of the photophores is important in the identification of benthic fish. Photophores in fish are primarily used to attract prey or confuse predators.
Within the parts of bony fish, the fins stand out. The dorsal, caudal and anal fins are odd because they have a position following the sagittal plane of the animal. The pectoral and ventral fins are paired.
Swim bladder of bony fishes
Bony fish also have a buoyancy organ called a swim bladder. It is a bag with flexible walls, filled with gas, located dorsally below the spinal column and above the digestive tract. It controls buoyancy through a complex system of gaseous exchange with the blood and allows the fish to ascend or descend in the water without the need to use the muscles. The swim bladder is made up of 1 or 2 chambers of gas glands.
If there is a connection (pneumatic duct) with the digestive tract, we speak of physostoma swim bladder The gases will be released into the digestive tract. On the other hand, if you don't have a connection, we talk about physioclist swim bladder, which will release the gases through the circulatory system. In both cases the bladder is highly irrigated.
Circulatory system of bony fishes
They have a simple circulatory system. In this circulation, blood only passes through the heart once in each revolution. The heart is tubular and shows a sinus venosus that collects blood, an atrium and a driving ventricle. The blood comes from the veins of the body loaded with carbon dioxide towards the heart. The ventricle pumps blood to the gills, where it is oxygenated and circulated through arteries to be distributed throughout the body. The return of blood to the heart is done through veins. The branchial artery carries blood to the gills for oxygenation. Therefore, the circulation in these animals is closed, simple and incomplete, that is, there is only one circuit and there will be mixing of blood.
Bony fish have special sensory organs called lateral lines. They consist of channels that run along the sides of the head and body and are connected to the outside by means of small pores. The main function of the lateral line is to detect very low-frequency vibrations, but in some species it can also detect low-power electric fields.
Bony Fish Habitat
Bony fish are aquatic animals. They need water to stay hydrated and to carry out breathing and other vital functions.
These animals have colonized all aquatic environments We can see them in freshwater such as rivers, lakes or lagoons, in the seas and oceans they can live at different levels, in the shallowest and deepest areas. Thus, there are s altwater bony fish and freshwater bony fish.
Bony Fish Feeding
Being such a large group of animals, there is a great variety in the diet. Some fish are herbivorous and feed on algae, others filter the water by taking small food particles. Some fish are true predators like tuna.
Bony fishes have a sense of tasteThis sense can extend to the level of the skin and also inside the mouth. They have chemoreceptors, which are taste buds that are scattered throughout the surface epithelium of the grooves of the papillae of the tongue. Each taste bud is made up of several dozen cells of various types: supporting cells, basal cells, and taste sensory cells. The apical surface of these cells is dotted with microvilli that protrude from the surface epithelium. Associated with these cells are also a series of nerve fibers that carry information to the brain.
Reproduction of bony fishes
In osteichthyes, male and female organs are not differentiated. Fertilization is almost always external and they are oviparous animalsFemales and males release their gametes to the outside and thus fertilize. Normally, the female lays her unfertilized eggs in a protected area, then the male fertilizes them by expelling his gametes on them. In the event that there is internal fertilization, the fish have an organ called gonopodium that serves as an anchor. Internal fertilization is very rare in these fish.
Examples of bony fishes
After reviewing the characteristics of bony fish, here is a list of the most representative examples:
- Sollo or common sturgeon (Acipenser sturio)
- American or Mississippi paddlefish (Polyodon spathula)
- Calabar Bichir (Erpetoichthys calabaricus)
- Catan (Atractosteus spatula)
- Nelma white salmon (Stenodus nelma)
- Danube salmon (Hucho hucho)
- Lusitanian Toadfish (Halobatrachus didactylus)
- Mackerel or mackerel (Scomber scombrus)
- Golden (Sparus aurata)
- European hake (Merluccius merluccius)
- Common Clownfish (Amphiprion ocellaris)
- Blue tang (Paracanthurus hepatus)
- Butterfly fish (Amphichaetodon howensis)
- Sunfish (Mola mola)
- Lemonfish (Seriola dumerili)
- Scorpion fish (Trachinus draco)
- Needlefish (Picudo gacho)
- Angelfish (Pterophyllum scalare)
- Guppy (Poecilia reticulata)
- Neon tetra (Paracheirodon innesi)
Bony fish pictures
And to get a better look at what bony fish look like, we're sharing a series of amazing images that match some of the examples above:
1. Sollo or common sturgeon (Acipenser sturio)
two. American or Mississippi paddlefish (Polyodon spathula)
3. Calabar Bichir (Erpetoichthys calabaricus)
4. Alligator gar (Atractosteus spatula)
5. Danube salmon (Hucho hucho)
6. Lusitanian frogfish (Halobatrachus didactylus)
7. Mackerel or mackerel (Scomber scombrus)
8. Sea bream (Sparus aurata)
9. Common Clownfish (Amphiprion ocellaris)
10. Blue tang (Paracanthurus hepatus)
eleven. Butterfly fish (Amphichaetodon howensis)
12. Sunfish (Mola mola)
13. Lemon fish (Seriola dumerili)
