Osteichthyes: Definition, Classification, Characteristics, Examples, Facts

Classification of Osteichthyes

Osteichthyes is a class of fish within the division Gnathostomata, which includes all vertebrates possessing jaws. 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 subclass:

Actinopterygii

Actinopterygii are the largest subclass of Osteichthyes, containing modern bony fishes. Their fins are supported by long, thin, bony rays. They have gills 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 are characterized by a skeleton made primarily of bone, unlike cartilaginous fish, which have cartilage-based skeletons. All types of fish, as well as recent tetrapods, are of common ancestry and thus display the typical vertebrate body plan.

Morphology and Anatomy of Osteichthyes

• 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.

• It is powered through an endoskeleton, which consists mostly of bone, used for 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 auricle and one ventricle) that ensures 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 lay eggs in water, and the baby fish look like small adults.

• Actinopterygii often practice external fertilization, where eggs and sperm are released into water.

• Sarcopterygii generally exhibit internal fertilization, with the transfer of sperm directly into the female's body.

• Eggs are laid in water, with protective coatings to prevent desiccation.

• Most species exhibit direct development, where the hatchlings resemble tiny adults, with no true metamorphosis.

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 behavior.

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 colors and territorial behavior.

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

Conservation And Environmental Impact Osteichthyes

The Osteichthyes 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. Such pressures disrupt the ecological balance that impacts not only fish species but also the larger environments in which they live, both in the marine and freshwater environments.

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

FAQs on Osteichthyes

What are Osteichthyes?

Osteichthyes, also known as bony fishes, are fishes whose skeleton is made mainly of bone rather than cartilage. They are the largest group of fishes and are found in a wide range of aquatic habitats, including freshwater lakes, rivers, and marine environments. Examples include Labeo (Rohu), Catla, Clarias (Catfish), Hippocampus (Seahorse), and Latimeria.

How are Osteichthyes classified?

Osteichthyes are classified into two main subclasses:

• Actinopterygii (ray-finned fishes) – These have fins supported by long, thin bony rays. They make up the majority of modern fishes, such as Rohu and Catla.

• Sarcopterygii (lobe-finned fishes) – These have fleshy, lobed fins with a bony skeleton inside, considered more primitive and closely related to amphibians. Example: Latimeria

What are the features of Osteichthyes?

They have a bony endoskeleton, a streamlined body, and gills covered by an operculum. The skin is covered with cycloid, ctenoid, or ganoid scales. They possess a swim bladder for buoyancy, are cold-blooded (poikilothermic), and usually exhibit external fertilisation with oviparous reproduction.

Explain the life cycle of Osteichthyes

The life cycle of Osteichthyes begins with external fertilisation, where eggs and sperm are released into the water. Fertilised eggs develop into embryos, which hatch into larvae. The larval stage is free-swimming and undergoes several developmental changes. As the larvae grow, they transform into juveniles, resembling adults. Juveniles continue to grow and reach sexual maturity, becoming fully developed adults capable of reproduction. This cycle then repeats with each breeding season.

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