Osteichthyes: Definition, Classification, Characteristics, Examples, Facts

Osteichthyes Classification: Kingdom to Class

Osteichthyes or bony fishes are a major class of vertebrates within the division Gnathostomata. Gnathostomata includes all vertebrates possessing jaws, making Osteichthyes (bony fishes) distinct from jawless fishes (Agnatha) and cartilaginous fishes (Chondrichthyes). They are classified under vertebrata, having a notochord only in the embryonic stage, and later replaced by a vertebral column in adults.

This class is further divided into two major subclasses:

Actinopterygii

Actinopterygii are the largest subclass of Osteichthyes, containing modern bony fishes. They have fins supported by long, thin, bony rays. Their gills are covered by an operculum. Examples include Carassius auratus (goldfish), Catla, Rohu, and Hilsa

Sarcopterygii

Sarcopterygii are a small subclass with paired fins that are fleshy and lobed. These fins are considered ancestral to the limbs of amphibians. They have a bony skeleton, cosmoid scales, and internal nostrils. Examples include Latimeria (Coelacanth) and lungfishes like Neoceratodus (Australian lungfish).

Characteristic Features of Osteichthyes

Osteichthyes or bony fishes are defined by a skeleton made of bone, unlike cartilaginous fish, which have cartilage-based skeletons. The bony skeleton provides strength, rigidity, and protection. All types of fish, as well as recent tetrapods, are of common ancestry and thus display the typical vertebrate body plan.

Osteichthyes: Morphology and Anatomy

Osteichthyes or bony fishes show diverse morphology and anatomy. Their body forms vary from streamlined shapes in fast swimmers to flattened shapes in bottom dwellers.

• The body shape of Osteichthyes ranges from streamlined forms in fast swimmers to flattened shapes in bottom dwellers. Different types of scales, ctenoid and cycloid, protect and reduce friction against the passage of water.

• Their fins - all dorsal, pectoral, pelvic, ventral, and caudal - are each specialised to help the fish stay balanced, turn, and move forward.

• The endoskeleton of osteichthyes is made mostly of bone, used for the protection and structural support of internal organs. This also features specialised muscles that enable efficient swimming, whether in red muscle used for sustained swimming or white muscle that provides the burst movements.

• It has a mouth, oesophagus, stomach, and intestine in the digestive system for digestion.

• The organism respires through the removal of oxygen from water using gills and gives out carbon dioxide, which is the byproduct formed during cellular respiration.

• The circulatory system is a closed-loop system with a two-chambered heart (one atrium and one ventricle) that ensures the proper functioning of body processes by delivering oxygenated blood throughout the body.

Life Cycle of Osteichthyes

The bony fishes have a simple life cycle. They grow from eggs (oviparous) into young fish and then into adults. Most Osteichthyes lay eggs in water, and the baby fish look like small adults.

• Actinopterygii (ray-finned bony fishes) often practice external fertilisation, where eggs and sperm are released into water.

• Sarcopterygii (lobe-finned bony fishes) generally exhibit internal fertilisation, with the transfer of sperm directly into the female's body.

Osteichthyes eggs are laid in water. Eggs have protective coatings to prevent desiccation. Most species show direct development, and hatchlings look like tiny adults. There is no true metamorphosis that occurs in bony fishes.

Examples of Osteichthyes

Osteichthyes live in marine as well as freshwater habitats. Some of them live in aquariums. Examples of bony fishes in different habitats are:

Marine Species

• Exocoetus (Flying Fish): It is known for its ability to glide above the water's surface.

• Hippocampus (Seahorse): These are unique for their upright posture and unique reproductive behaviour.

Freshwater Species

• Labeo rohita (Rohu): A popular fish in South Asian aquaculture.

• Catla catla: A large freshwater fish native to the Indian subcontinent.

• Clarias batrachus (Magur): A species of catfish found in freshwater habitats.

Aquarium Species

• Betta splendens (Fighting Fish): These are known for their vibrant colours and territorial behaviour.

• Pterophyllum scalare (Angelfish): They are recognised for their graceful swimming and distinctive body shape.

Conservation And Environmental Impact of Osteichthyes

Osteichthyes or bony fishes are under great threat from overfishing, habitat destruction, and pollution. All these factors contribute to the decline in fish populations and loss of biodiversity in aquatic ecosystems. These pressures disrupt the ecological balance that impacts not only fish species but also the larger environments in which they live.

To protect them, various conservation efforts have been made. For example, fishing quotas, marine reserves, and other sustainable ways of catching fish. In the same way, habitat restorations render damaged ecosystems safe again. These actions aim to conserve fish populations and protect their habitats for the future.

Osteichthyes NEET MCQs

Q1. Which is not the feature of Osteicthyes ?

1. Swim bladder present

2. Gill slits show presence of Operculum

3. Placoid scales are present

4. Endoskeleton is made up of Bone

Correct answer: 3) Placoid scales are present

Explanation:

Osteichthyes are a class of fish characterized by having an endoskeleton made of bone rather than cartilage, as seen in cartilaginous fish (Chondrichthyes). Osteichthyes include a wide variety of species, with two major groups: ray-finned fish (Actinopterygii) and lobe-finned fish (Sarcopterygii). Examples of Osteichthyes include species like the hippocampus (seahorse) and the betta (betta fish). These fish possess a bony skeleton, and a swim bladder for buoyancy, and are found in diverse aquatic environments around the world.

Hence the correct answer is option 3) Placoid scales are present.

Q2. Osteichthyes are cold blooded , that is they are

1. Homiotherms

2. Poikilotherms

3. Heat escape from body and then remain cold

4. They live in water

Correct answer: 3) Poikilotherms

Explanation:

Osteichthyes, usually called bony fish, are cold-blooded or poikilothermic animals. Their body temperature, therefore, depends on environmental conditions rather than physiological processes. Metabolic rates and activity levels vary according to water temperatures in such organisms. This makes them perfect for all kinds of aquatic habitats, but they are also sensitive to temperature changes, which affect their survival and distribution in several ecosystems.

Hence the correct answer is Option 2) Poikilotherms.

Q3. Which of the following animals has a two-chambered heart?

1. Labeo rohita

2. Salamander

3. Chelone

4. All of these

Correct answer: 1) Labeo rohita

Explanation:

Salamander and Chelone (commonly called Lizard) belong to the group Amphibia and Reptiles, which shows 3 chambered hearts (two auricles and one ventricle).

Labeo rohita is a true fish and fishes have a two-chambered heart.

Hence, the correct answer is option 1) Labeo rohita.

Also Read:

• MCQs on Class Osteichthyes

• Phylum Platyhelminthes

• Differences between Coelomate and Acoelomate

Recommended Video for Osteichthyes