Teleost fish: Characteristics, types, reproduction and more…..

 Main Characteristics of  The Teleost Fish

Defining teleost fishes by functional morphology is hard, since they have evolved into many diverse shapes. The structure of the tail and the efficiency of the swimming mechanism are the main traits that distinguish teleosts from other, “lower,” fishes.

The difference between teleosts and other bony fish lies mainly in their jaw bones; teleosts have a movable premaxilla and corresponding modifications in the jaw musculature which make it possible for them to protrude their jaws outwards from the mouth. This is of great advantage, enabling them to grab prey and draw it into the mouth.

In general, it’s worth mentioning that teleost fish have a partially or completely ossified skeleton depending on the species.

Generally, its body is spindle-shaped, that is, it’s wide at the cranial end and laterally depressed at the caudal part. With this particular anatomy the fish manages to have greater mobility in the water without consuming much energy.

Other body shapes that can occur in teleost fish are the oval, serpentiform (as in the case of eels , ) flattened back ventrally like the soles and we also get accentuated shapes such as those of the abyssal fish and the sea horses.

Their external anatomy can be clearly divided into three regions: head, trunk and tail. The head is located between the cranial end of the mouth and the edge of the operculum, which is a hyoid arch that covers the gills.

Body

The trunk of a teleost fish can vary in length depending on the species, but generally extends from the edge of the operculum to the vertical that runs through the anus.  Moreover, teleost fish have a dorsal fin, two pectoral fins and two pelvic fins.

The tail is the last portion of the body that covers from the anus to the caudal fin. It contains the caudal peduncle, which is the narrow part of the body.

The caudal peduncle is an adipose muscle that plays an important role in the movements and ability of animals to swim.

In the final part of the teleost fish there are one or more anal fins that are usually located behind the anal opening.

Each set of fins is attached to the body differently. The pectoral and pelvic fins are joined by bone belts; which in some species have joined with the skull and thorax through the evolutionary process.

On the other hand, the dorsal and anal fins have small bones embedded in the intermuscular septa by which they are held. Finally, the caudal fin is held by several caudal vertebrae that merged.

Each fin in the same way can be spiny or soft. The spiny ones, which are part of the body of the most evolved species, are common bones that give it hardness.  On the other hand the soft rays are made up by two skin components.

Skin

The entire body of the teleosts fish  is covered by a layer of skin that protects them from any disease or injury. It’s divided into several layers that give it thickness and firmness. Each of them is described in detail below:

♠ The first layer is the epidermis, which is covered by a cuticle and is the outermost part of the skin.

♠ Then there  is the dermis that is the layer from which the scales are born.

♠ The dermis rests on the hypodermis, which is a lax fat layer responsible for joining the skin with the other interior structures.

It’s worth mentioning that the skin of a teleost is largely impermeable to water, and the main interface between the fish’s body and its surroundings is the gills.

Dermis Structure

The cuticle of the dermis of the teleost fish is very thin, measuring only one micrometer but it’s more complex than it seems. It’s made up of mucopolysaccharides that are the result of the combination of both cellular material and desquamated cells and mucus that is secreted to the surface through epidermal cells.

Similarly, this cuticle can contain very specific immunoglobulins such as free fatty acids, lysozymes and some different substances that are capable of protecting the specimens against malignant pathogens.

The mucus is present in large quantities in some species to make the skin less permeable and that the osmosis process can be carried out successfully.

The mucus also helps protect teleost fish against abrasion, decreases the friction force while reducing the action of irritants, so its role is essential against fungi and bacteria. In some species it can intervene in communication.

The dermis is made-up of two layers, a superficial one which is the connective tissue responsible for giving color to the skin. The second layer is deeper (a collagen matrix),  and gives structural strength to the skin. It’s here where the scales that are later covered by the epidermis originate.

Epidermis

This layer is composed of a squamous epithelium with basic Malpigium cells which are very common structures in all teleost fish.

They also have goblet cells that are responsible for secreting the mucus. Its thickness can range from 3 to 20 cells depending on the species. The less scales, or in cases where the skin does not have scales as in cartilaginous fish, the thickness of this layer is greater.

Scales

As stated earlier, these originate in the dermis intricately with each other and then are covered by the epidermis. The scales aren’t  usually in the head but only in the body.

These are calcified flexible plates that can serve as a calcium supplement in case the animal needs it.

They have an outer bone crest but inside they are made of a connective tissue that is usually fibrous, which is known as collagen. This last part is not calcified or in some cases only a portion of it, depending on the species.

Importance of scales

If the fish lose the scales they lose the epidermis, resulting in problems for the regulation of body fluids, or what is the same for osmotic regulation.

Teleost fish can have two types of scales; the ctenoid scales that are usually present in teleost fish with spiny rays.  Such structures have a particular comb shape.

There are also cycloid scales that are present in teleost fish with a soft radius. These ones have a more or less circular shape, which makes them different from the previous ones.

In spite of being different they resemble due to their continuous growth during the life of the fish; for this reason they are marked with rings on the surface.

This pattern can help determine the age of the fish in many types of species. We invite you to read our article the anatomy of fish to learn more about the diiferent types of scales in fishes

Senses

In teleost fish, olfactory receptors are limited to the nostrils located in the front. Smell is used as a sense of distance that allows them to perceive the presence of prey and close predators while being used in some species to orient them during migrations such as the case of salmons

But in the case of the sense of taste, taste receptors aren’t restricted only to the mouth and can often be found in the head and even in the chest.

The beards of many teleost fish are usually specialized taste buds in addition to fulfilling the function of being thermal and mechanical receivers.

On each side of the body of the teleost fish there is usually middle and a dorsal lateral line. These lines are joined in the head, having the function of a “super-ear” making it possible to capture small vibrations in the surroundings being able to locate remote objects or navigate in dark waters.

This sharp sense also allows them to detect prey and predators that are in the distance. As a classical auditory system, they have an inner ear made up of a maze.

The eyes of teleost fish are usually round and have a very simple structure lacking eyelids and tear glands. They are able to see only at short distances and in low light, so they have developed mostly other senses to orient and realize what is happening around them.

To focus the gaze on a point, instead of modifying the curvature of the lens, as human eyes do, the fish does so by bringing the lens closer or apart thanks to the ligament responsible for holding it.

Breathing

Despite what people may think, teleost fish do require oxygen to breathe. However, this element is present in water, although to a much lesser extent than what can be found on the earth’s surface, since water has approximately 5 ml of oxygen per liter.

In order to take full advantage of this vital element, the fish have developed a very ingenious system of breathing that is based on the presence of gills which are located between the mouth and the pharynx.

When the mouth opens, water floods the gills of these fish which, through the blood vessels that make them up, allow oxygen to reach the blood.

Generally teleost fish have an organ called an operculum, which covers the gills on the outside of the body.

This closes when the mouth opens, preventing the water from coming out again. Once the mouth closes the operculum opens allowing the liquid to reach the gills.

But there are some cases of teleost fish with a different breathing system, such as tuna . This fish must keep its mouth open for longer so that the oxygen that the oxygen in water reaches the blood. Such a species has deoxygenated blood in the gills that will fill with oxygen while water passes through the membranes.

The most curious thing about this system is that the exchange of elements and processes is carried out through countercurrents, that is, the water carries one direction while the blood goes in the opposite direction; In this way the process is improved and can be used in the same way to remove waste from the blood to the water.

The fish’s habitat influences its breathing

Water temperature tends to be a relevant factor in oxygen content since when the water is very hot there is less of this important element. For this reason, teleost fish that need more oxygen to survive are present in cold water, while fish that inhabit hot waters merit less oxygen.

For this reason, when it’s decided to have a fish as a pet the water conditions and its temperature should not be taken lightly. In this sense, knowing the habitat and requirements of animals can play a fundamental role in the proper development of pets or can lead to their death.

let’s learn more about gills

Internal anatomy

Generally, most of the specimens that belong to the genus of teleost fish have swim bladder, a derivative of ancestral lungs. This structure is located in the anterior part of the intestine, below the spine.

It’s shaped like a sack and is filled with a mixture between oxygen and nitrogen extracted from the blood, which allow the fish to stay at the depth it  wants without this involving extra effort.

This is a typical characteristic of teleost fish, since in benthic and deep sea fish it may be reduced or even not present..

There are many names of teleost fish and in some species of them the swim bladder is connected to the digestive tract allowing them to take gas from the surface to fill and use it. In other species this pneumatic duct is absent.

In addition to the general function of allowing the fish to immerse themselves in water, in species of teleost fish such as catfish, carp and piranha .this organ fulfills an important task in the perception of sound waves, by connecting with the ear through a series of modified bones in the vertebrae that is called Weber’s apparatus. In fish such as sea bass, the swim bladder is also used to produce sounds.

How Teleost fish Reproduce?

Teleost fish can have different types of mating and reproduction patterns depending on the species. In addition, this process is influenced by : water temperature, food and some other external factors. The fish can be:

• Oviparous.
• Viviparous.
• Ovoviviparous.

Oviparous fish usually drop eggs and sperm packets directly so that when they cross they fertilize on their own. In some cases the density of the eggs is higher and they reach the bottom of the water, but at other times they are light or with oil to float.

This type of fish can protect its eggs in bubbles that stick to the plants until they hatch, or they can collect the eggs in their mouths to protect them until they are to be born.

This is the case of surgeon fish, carp fish and needlefish.

Viviparous fish are capable of calving offspring that are fully formed, since the incubation process of the eggs is carried out within the pregnant female.

It’s important to point out that during the offspring’s maturation process the mother provides the necessary nutrients for the development; which is a very similar process to that of mammals.

Finally, in ovoviviparous fish, fertilization is done internally, by introducing the male’s gonopodium into the female, putting the eggs in it, as in the case of viviparous. The main difference is that while the offspring are in the womb they will feed on a yolk sac until they leave.

For a second time the female won’t need the male since she will keep sperm inside her.

Generally, these species of teleost fish have many young in each birth, although once the fry are born they run the risk of being eaten by their parents. These species within the teleost fish genus are very easy to maintain and are the favorites of aquarium fans, the most popular being guppy and molly.

Teleost Fish: Feeding Patterns

Due to the number of species that are grouped in the teleost fish genus, it’s impossible to determine a single feeding trend for the entire group. Consequently, their diet is varied, as well as the prey they prefer to catch.

Carnivores

There may be predatory carnivorous teleost fish such as catfish that feeds on other smaller fish and even land animals such as frogs and small insects that perch in the water.

There are also carnivorous teleost fish that live more located towards the bottom of shallow water and therefore feed on small worms, insect larvae, crustaceans, polychaetes or even snails.

These fish usually have sharp saw-shaped teeth that help them catch and swallow whole prey, although in many cases they chop it for better digestion.

They generally have two types hunting techniques according to the species.

There are those teleost fish that hunt and chase  their prey for which they must be able to swim quickly. however many species attack schools of smaller fish to ensure food.

Another widely used method is stalking, lure and camouflage to wait for the victim and devour it.

Omnivores

These fish are characterized by eating meat and plants, their diet being much more extensive and varied. They can ingest insects, larvae, worms as well as plankton and small bacteria and microscopic animals.

These fish are usually great opportunists, able to adapt to the environment and the circumstances in which they live. But they differ from carnivorous fish by limiting their feeding to small invertebrates but not eating other fish.

Herbivores

They are those that base their diet on plankton, vegetables, algae, microalgae and phytoplankton.  Their food intake will vary depending on the depth to which they live.  This group makes-up the basis of the food pyramid in fish, since they can serve as food for larger species.

The biggest peculiarity of these fish is that they can spend the whole day eating, due to the small amount of nutrients they get from their food.

It worth mentioning that due to this constant intake their digestive system stays in operation all day.

But despite the fact that its diet consists mainly of plants, it’s difficult to speak of strict herbivorous fish since many interspersed the intake of herbs with animal feed.

Detritivorous

These animals are often also called water cleaners, since their diet is based on decomposing organic matter as well as dead fish that are at the bottom of the water.

These teleost fish are very popular in the world of aquarium hobby because they represent a significant help in cleaning and improving the water in the tank.  

Moreover, they tend to be very calm and peaceful, getting along with almost any other species of fish.

We invite you to read our article freshwater Barracudas to learn about these detritivorous species

Filter Fish

Another large group of teleost fish are able to eat thanks to water filtration, ingesting zooplankton, of animal origin, or phytoplankton, of plant origin. Since it’s impossible for these fish to differentiate between one and the other, they can be considered omnivorous fish.

To carry out this process they must ingest large amounts of water that will then be filtered to trap all the microscopic organisms that inhabit it.

A very common case of these fish are sardines and anchovies. These species have gills called gill hooks responsible for forming a filter in which food is trapped to take it to the esophagus and digest it.

Let’s learn about this topic

Digestive system

It’s made-up by a series of organs that fulfill specific functions and depend on each other to carry out their processes.

Mouth

Some species of teleost fish lack teeth, or if they have them such structures are small. They can be Vomerian, that is, they are located in the upper palate or they can be maxillary, which are in the tongue or pharynx fulfilling a crushing function.

The teeth generally serve more to capture the food than to chew it and are more developed in carnivorous teleost fish that are such as the goldfish and the tararira. In these cases the mouth is large and terminal.  They do not have salivary glands but mucous membranes.

Pharynx, esophagus, stomach, intestine and liver

There are examples in teleost fish where the pharynx is generally a filter, which prevents water particles from reaching the delicate gill filaments.

The esophagus is the organ that communicates the pharynx directly with the stomach. It’s thick-walled, which allows it to be enlarged in case a thick dam or large amount of food must pass.

On the other hand, the stomach usually has a different shape and size depending on the species of teleost fish.

In the case of predatory and carnivorous fish, this organ is wide with distensible walls and capable of expanding to facilitate the entry of large prey. The exit to the stomach is limited by the pylorus.

In examples of teleost fish such as salmonid, the food that enters the stomach is crushed by the action of acids, digestive enzymes and the crushing action of the stomach walls.

Around it are located a series of structures that are called pyloric blinds, which are surrounded by white adipose tissue. Its function is to absorb and neutralize acidity to create a greater space for digestion.

In this type of teleost, enzymes must absorb the fats, proteins and sugars that, after crossing the intestinal wall, are taken to the liver. The rest of the foods such as fibers, snails and other unnecessary materials are evacuated with feces.

other traits

The length of the intestine varies according to the food consumed by each type of teleost fish, being shorter in predatory fish while in the phytophagous or herbivores it’s longer.

In addition to this, the time the food spends in the intestines can vary, ranging from a few hours to full days depending on the water temperature. The hotter the water, the faster the fish’s metabolism.

On the other hand, the liver can intervene in different metabolic processes. It’s white, with a reddish brown color, in some cases it can be presented in cream pink, and is very bulky. The gallbladder is well developed, with the bile duct responsible for pouring bile into the first part of the small intestine so that it emulsifies fat and can be attacked by pancreatic lipases more easily.

Economic Importance of Teleost Fish

Teleosts are economically important in different ways. They are captured for food throughout the world. A small number of species such as herring, cod ,haddock, anchovy, tuna and mackerel provide people with millions of tons of food per year, while many other species are fished in smaller quantities.

Teleots  also provide a large proportion of fish caught for sport. Commercial and recreational fishing together provide millions of people with employment.

A small number of productive species, including carp, salmon, tilapia  and catfish are grown commercially, producing millions of tons of protein-rich foods per year.

From the United Nations for Agriculture and Food, production is expected to increase sharply, so by 2030, perhaps sixty-two percent of food fish is grown.

Fish are consumed fresh, or can be preserved by traditional methods, which include combinations of drying, smoking, and salting, or fermentation. Modern preservation methods include freezing, lyophilization and heat treatment (as in canning). Frozen fish products are breaded or battered fillets, fish sticks and croquettes.

Fishmeal is used as a food supplement for farmed fish and livestock. Fish oils are made either from fish liver, especially rich in vitamins A and D, or fatty fish bodies such as sardines and herring, and are used as food supplements and for the treatment of deficiencies of vitamins

Some of the smallest and most colorful species serve as aquarium samples and pets while sea lions are used in the leather industry.

Always remember to enjoy nature responsibly since there are many species endangered nowadays… If you do so we can still enjoy something like this