Pisces: Overview | Zoology Optional Notes for UPSC PDF Download

Introduction to Pisces

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Characteristics of Pisces

1. Habitat Diversity: Pisces are adaptable to various aquatic environments, including freshwater, marine, and brackish water.
2. Body Shape: They commonly have a streamlined body, although some species exhibit spindle-shaped or elongated forms.
3. Body Division: The body is divided into distinct regions: head, trunk, and tail.
4. Locomotion: Swimming is primarily facilitated by the tail, a crucial locomotor structure.
5. Fins: Paired and unpaired fins serve as appendages that aid in balance and maneuverability.
6. Lateral Line System: Pisces possess a lateral line system, functioning as a sensory organ to detect disturbances in the surrounding environment.
7. Scale Protection: The body is covered in thick-seated scales, which offer protection to internal organs.
8. Respiration: Gills serve as respiratory organs, allowing Pisces to extract oxygen from water.
9. Circulation: They exhibit closed-type blood circulation.
10. Skeletal Diversity: Pisces may have bony or cartilaginous internal skeletons.
11. Ectothermic Nature: Pisces are cold-blooded organisms, meaning their body temperature is regulated by the environment.
12. Feeding Habits: They can be herbivores or carnivores, and reproduction can be oviparous or ovoviviparous.
13. Sexual Dimorphism: Pisces have separate sexes.
14. Fertilization: Fertilization can be external or internal.
15. Embryonic Features: They lack extra-embryonic membranes.
16. Digestive System: Pisces have a well-developed digestive system.

Torpedo

Classification of Pisces

• All members of this class are now extinct.
• They had an exoskeleton in the form of shields and a bony endoskeleton.
• Autodiastylic jaw suspension was a characteristic feature.
• Placoderms survived until the end of the Devonian period.
• Heterocercal caudal fin was present.
• Examples include Climatius and Bothriolepis.

• These fish are exclusively found in marine environments.
• They possess an exoskeleton composed of placoid scales.
• The endoskeleton is cartilaginous.
• Jaw suspension follows the amphistylic pattern.
• Gills serve as their respiratory organs.
• They exhibit a heterocercal caudal fin.
• Males have claspers as reproductive organs.
• Air bladders are absent.
• Chondrichthyes are divided into two sub-classes: Selachi and Bradyodonti.

• Osteichthyes are found in marine, freshwater, and brackish water environments.
• They possess a bony endoskeleton.
• Autostylic jaw suspension is a defining feature.
• Claspers are absent in males.
• Gills are covered by an operculum.
• Many species have air bladders.
• They are further categorized into two sub-classes: Crossopterygii and Actinopterygii.
• Examples include Proptopterus and Lepidosiren.

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Key Differences Between Pisces Classes

These differences highlight the distinctive features of each class within the Pisces group, aiding in their taxonomic classification.