Chapter 24 - Fishes

Chapter 24 - Fishes

Contributions of Fishes

• Vertebral Column:
      - Encloses the spinal cord and protects the brain.

• Gills:
      - Essential for respiration in aquatic environments.

• Advanced Nervous System:
      - Enhanced sensory capabilities including smell, taste, and hearing.

• Jaws with Teeth:
      - Advanced feeding mechanisms compared to earlier vertebrates.

• Paired Pectoral and Pelvic Limbs:
      - Allow for improved locomotion and stability in water.

Class Myxini (Hagfishes)

• Anatomy:
      - Figure 24.3 illustrates key anatomical features.
      - Characterized by a strong sense of smell, but are blind.

• Defense Mechanisms:
      - Exude slime as a form of defense.

• Reproduction:
      - Details about reproductive strategies are not specified.

Structure and Features of Myxini

• Mouth:
      - Surrounded by barbels which help in sensory detection.

• External Gill Opening: Provides entry for water to flow over gills.

• Caudal Fin:
      - Structure aiding in swimming.

• Pores of Slime Sacs:
      - Openings from which slime is exuded.

Class Cephalaspidomorphi (Lampreys and Eels)

• Predatory and Parasitic Behavior:
      - Some species exhibit predatory behavior while others are parasitic.

• Anatomical Features:
      - Tongue: Possesses lingual cartilage.
      - Pharynx: Important for feeding.
      - Buccal Funnel with Keratinized Teeth:
          - Used for attachment to host fish and for rasping flesh.

Migration Patterns in Types of Fish

• Anadromous:
      - Fish that live in lakes or oceans and spawn upstream (e.g., salmon); adults typically die after spawning.

• Catadromous:
      - Fish like eels that live in freshwater streams but migrate downstream to lakes for reproduction.

Class Sarcopterygii (Lobe-Finned Fishes)

• Characteristics:
      - Represent extremely old lineage of primitive fishes.
      - Includes seven species such as lungfishes and coelacanths.

• Lungfish:
      - Able to survive out of water; can burrow in mud and exude slime to form a protective cocoon during dry periods.
      - Types of Lungfish:
          - Australian lungfish
          - African lungfish
          - South American lungfish

• Coelacanths:
      - Existed approximately 350 million years ago; thought to have gone extinct 70 million years ago, but were later found off the coasts of Africa and Indonesia.

Superclass Chondrichthyes (Cartilaginous Fishes)

• Examples:
      - Includes sharks, rays, and skates, totaling around 850 species.

• Skeletal Composition:
      - Lacks bone altogether; the endoskeleton is made of cartilage.

• External Anatomy:
      - Figure 24.8 details the major external features.
      - Exhibit rolling tooth replacement.

• Form and Function:
      - Possess pectoral and pelvic fins, and structural adaptations such as claspers.
      - Lateral Line System:
          - Used for detecting vibrations and maintaining equilibrium in water.

Scale Types in Fishes

• Placoid Scales:
      - Characteristic of cartilaginous fishes; leathery and hydrodynamic in structure.

• Other Scale Types:
      - Ganoid scales (non-teleost bony fishes)
      - Cycloid scales (teleost fishes)
      - Ctenoid scales (teleost fishes)

Sensory Adaptations

• Ampullae of Lorenzini:
      - Organs for electroreception enabling fishes to sense electrical fields.

• Spiracles (found in rays):
      - Serve as an intake for water to assist gill respiration.

Internal Anatomy of Cartilaginous Fishes

• Digestive System:
      - Contains a spiral valve which slows food passage and increases absorption efficiency.

• Cardiovascular System:
      - Features a two-chambered heart.

• Reproductive Strategies:
      - Internal fertilization is common among these species.

Superclass Osteichthyes (Bony Fishes)

• Teleosts:
      - The modern lineage of bony fishes with over 30,000 species.

• Bone Structure:
      - Endochondral bone: In which bone replaces cartilage in the endoskeleton.

• Operculum:
      - Bony plates covering the gills, increasing respiratory efficiency and protecting the gills.

Class Actinopterygii (Ray-Finned Fishes)

• Characteristics:
      - Comprise 30,000+ species.
      - Figure 24.15 provides a detailed anatomy illustration.

• Swim Bladder:
      - Functions in buoyancy and respiration.

• Pharyngeal Jaws:
      - Enhance predation by improving the ability to capture and consume prey.

Fin Types in Bony Fishes

• Heterocercal Tail Fin:
      - Tail fin with an unequal lobe structure (Figure 24.16).

• Homocercal Tail Fin:
      - Tail fin with equal lobes.

• Diphycercal Tail Fin:
      - Tail fin that tapers at both ends.

Vibrational Mechanics

• Weberian Ossicles:
      - A structure connecting the swim bladder with inner ear and brain, enhancing sound detection.
      - Vibrates in response to sound waves, facilitating communication and environmental awareness.