Bony fish: characteristics, classification, examples, habitat, differences and curiosities

In the immensity of seas, rivers and oceans, the bony fish (osteichthyes) constitute the largest and most diverse group of aquatic vertebrates. These fascinating creatures come in an astonishing variety of shapes, sizes, and colors, and are present in every aquatic habitat on the planet, from the coldest polar waters to the deepest seabeds. But what truly defines them and separates them from other groups? de peces, such as cartilaginous or jawless? Through this article, we explore in depth the Characteristics, classification, examples, and key differences between bony and cartilaginous fish, as well as little-known curiosities about their biology and adaptation.

What is a bony fish?

The bony fish, scientifically known as Osteichthyes, constitute a group of gnathostome vertebrates (i.e., equipped with articulated jaws) whose main characteristic is the presence of a internal skeleton formed predominantly by calcified bone, unlike cartilaginous fish, whose skeleton is flexible and made of cartilage. Furthermore, they possess considerable adaptation to aquatic life, with anatomical and physiological details unique within the animal kingdom.

This group comprises the majority of the fish present both in sweet waters , the salads. It is common for fish for human consumption (such as salmon, carp, tuna, or sea bream) to be bony fish, as are most ornamental aquarium species.

When classifying fish, three large groups are distinguished:

• Bony fishes (Osteichthyes): Bone skeleton and great diversity of species.
• Cartilaginous fishes (Chondrichthyes): Cartilage skeleton, example sharks, rays and manta rays.
• Jawless fish (Agnatha): A small group, such as lampreys and hagfish, characterized by the absence of jaws and an elongated appearance.

Classification of bony fish

The scientific classification of bony fish reveals a complex and fascinating evolutionary structure:

• Class Actinopterygii (ray-finned fish):
  • Subclass Chondrostei: Includes sturgeons and primitive fish.
  • Subclass Neopterygii:
    • Infraclass Holostei
    • Infraclass Teleostei: Represents the vast majority de peces modern.
• Class Sarcopterygii (lobe-finned fish):
  • Subclass Coelacanthimorpha: the coelacanths.
  • Subclass Dipnoi: Lungfish.
  • Subclass Tetrapodomorpha: It includes the ancestors of terrestrial tetrapods.

Actinopterygians They comprise the majority of extant species, characterized by fins supported by bony rays. Sarcopterygian They include more primitive species with lobed fins, directly related to terrestrial vertebrates.

Main characteristics of bony fish

1. Skeleton and bone structure
   The body is divided into axial skeleton (spine), cephalic (skull), zonal (fin anchorage) and appendicular (fins). bone skeleton provides strength, protection and efficient swimming ability.

   Unlike cartilaginous fish, osteichthyes have ossified vertebrae and differentiated ribs, allowing greater muscular rigidity and flexibility.

2. Gills and breathing
   They have gills within a branchial chamber lined by a operculum mobile, which facilitates protection and the flow of water necessary to extract oxygen.
   In some cases, the gills transform into primitive lungs or the swim bladder takes over part of the breathing.
3. Mouth, teeth and jaws
   Terminal mouth, articulated and very precise. teeth They emerge from dermal bones and are generally not replaced once lost, unlike sharks.
4. Scales
   They cover the body and there are different types depending on the evolution:
   • Cycloids: Smooth edges, typical of primitive species.
   • Ctenoids: Combed edges, in modern species.

   These scales act as a defense, reduce friction and help in species identification (especially by the lateral line).

5. fins
   They have several pairs (pectoral, pelvic) and unpaired fins (dorsal, anal, caudal). Depending on the position of the pelvic and thoracic fins, we distinguish between abdominal, thoracic, jugular, and apodal fins.
6. Swim bladder
   A gas-filled internal organ that regulates buoyancy and allows the fish to remain suspended without expending energy. In some species, it develops into a lung.
7. Nervous system and sensory organs
   highlights the lateral line, specialized in detecting vibrations and movements in the water. In addition, chromatophores in the skin allow for variety and camouflage depending on the habitat.
8. Skin and coloration
   The epidermis contains mucous glands and chromatophores, generating characteristic colors, mimicry and signals during reproduction.

Among other adaptations, some species exhibit unique morphologies, from hydrodynamic bodies in powerful swimmers to mimetic forms in fish that live in deep waters or in complex environments.

Feeding of bony fish

There are a great variety of Feeding Habits:

• Carnivores: They are predominantly those with large stomachs, pyloric caeca, and a short intestine. Examples include salmon, trout, and hake.
• Herbivores: Simple stomach and long intestine. Example: parrotfish, some carp.
• Filters: They capture plankton, using modified gill arches.
• Omnivores: They combine animal and vegetable diet.

The type of dentition and the digestive system depends on diet. Some fish have lost or modified their teeth depending on their food (as occurs in filter feeders), while predators have conical teeth or specialized shapes for cutting, crushing, or sucking prey.

Habitat of bony fishes

Bony fish have colonized all the aquatic environments known:

• Fresh waters: Lakes, rivers, ponds, and streams. Examples: carp, pike, tench.
• Salt waters: Oceans, seas, and estuaries. Examples: sardines, tuna, grouper.
• Brackish waters: Transition zones between fresh and salt water, such as estuaries and mangroves.
• Extreme environments: Some species live in deep waters, polar zones, warm tropical waters or in conditions of high salinity and pressure.

Their ability to adapt has allowed the evolution of species with unique characteristics, such as being able to withstand low temperatures, endure great pressures in the deep ocean, and live in low-light environments.

Reproduction of bony fish

• Predominant sexual reproduction: Males and females are differentiated, although dimorphism is often difficult to distinguish in many species.
• Frequent external fertilization: Eggs and sperm are released into the water, although there are exceptions to internal fertilization (males with adapted fins).
• Varied reproductive strategies: Mainly oviparous (they lay eggs), but there are also ovoviviparous and viviparous species.
• Sequential hermaphroditism: There are species that change sex during their life, favoring the survival of the group.
• Parental care: Rare, but present in some species that guard eggs or young until they are born.

Differences between bony fish and cartilaginous fish

• Skeleton: Bony in osteichthyans; cartilaginous and flexible in chondrichthyans.
• Scales: Cycloid, ctenoid, or ganoid scales in bony fish; placoid or dermal denticles in cartilaginous fish.
• Breathing: Bony fish have gills protected by an operculum; cartilaginous fish have unprotected gill slits and additional spiracles for water intake.
• Swim bladder: Present in most de peces bony, absent in cartilaginous (these regulate buoyancy using their high-fat liver or by swimming constantly).
• Caudal fin: Homocercal (equal lobes) in bone, heterocercal (unequal lobes) in cartilaginous.
• Reproductive strategies: Oviparous, ovoviviparous, or viviparous, with predominantly external fertilization in bony animals; internal fertilization and a smaller number of more developed offspring in cartilaginous animals.
• Sensory organs: Lateral line in both, but in cartilaginous animals the Ampullae of Lorenzini stand out for detecting electric fields.

Examples de peces bone

The variety of bony fish It is vast, encompassing well-known and consumed fish, as well as ornamental and exotic species. Some notable examples are:

• Salmon: Popular for its nutritional value and spectacular migrations.
• Trout: It inhabits cold waters, both fresh and brackish.
• Tent: Common in aquariums and food.
• Tuna: Ocean sprinter, key to the human diet.
• Golden: Highly appreciated in Mediterranean cuisine.
• Sea bass, sardine, mackerel, horse mackerel, bonito, hake, clownfish: Additional examples of great ecological, economic and ornamental importance.

Curiosities, adaptations and diversity in bony fish

• Mimicry and coloration: Many species have chromatophores that trigger color changes for camouflage or reproductive signals. Example: sole and reef fish.
• Unique body shapes: Some exhibit extreme adaptations, such as the porcupine fish, which inflates itself to defend itself, or the flying fish, which escape predators by gliding over the water.
• Electric organs: In families such as Gymnotidae (electric eels) there are organs capable of generating electrical impulses to detect prey or communicate.
• Multifunctional swim bladder: In addition to regulating buoyancy, in some species it acts as an acoustic organ to emit or perceive sounds.
• Reproduction variability: Strategies such as nest building, mating with dances, sex change (sequential hermaphroditism), and development of young in the parent's mouth or bladder.

Ecological and economic importance of bony fish

• Key in food chains: They occupy all nutritional levels, from top predators to herbivores and filter feeders, determining the structure and health of aquatic ecosystems.
• World fishing base: They constitute the majority of commercial and subsistence catches, as well as ornamental species in the aquarium hobby.
• Environmental indicators: Their abundance, diversity and health reflect habitat conditions and water quality.

Taxonomy and evolution of bony fishes

• Appearance in evolutionary history: The first bony fishes arose long before terrestrial amphibians, evolving from lobe-finned ancestors.
• Pelvication: Many bony fishes can migrate between fresh and salt water, such as salmon, eel, and sea trout, showing a unique adaptation to changes in salinity.

Bony fish represent the ultimate expression of adaptation and diversity in the aquatic world. Their ecological, biological, and economic role remains fundamental to the balance of ecosystems, human nutrition, and our understanding of vertebrate evolution. Observing their richness of forms, functions, and behaviors is like delving into one of the most fascinating chapters in natural history.