Fish and Amphibian Anatomy and Biology

Fish Anatomy and Physiological Systems

• Olfactory lobe: Senses chemicals in the water.
• Nostrils: In mammals, they connect with the throat; in fishes, they do not, so they take water through their mouth.
• Spiracles: Rays and bottom-dwelling fishes take water through these openings.
• Internal Organs: Fishes possess a 2-chambered heart and kidneys that regulate blood chemistry and remove waste.
• Liver: Stores surplus nutrients and detoxifies substances; in sharks, it aids in buoyancy.
• Swim bladder: Filled by gulping air from the surface or secretion through the bloodstream.
• Spiral valve: Found in sharks to increase surface area for digestion.

Scales and Integument

• Placoid (denticles): Tooth-like structures with a sandpaper texture.
• Ctenoid scales: Thin, translucent scales with alternate depressions.

Amphibian Classification and Status

Orders of Amphibia

• Caudata: Salamanders and newts.
• Anura: Frogs and toads.
• Apoda: Caecilians.

Amphibians are ectotherms that undergo metamorphosis; water is essential for their reproduction.

Conservation Status

Approximately 32% of species are threatened. Data indicates 43% in decline, 1% increasing, 27% stable, and 29% unknown. Of the 68% not threatened (3,887 species), 8 are critically endangered, 13 are endangered, 12 are vulnerable, and 67 are not considered threatened.

Fish Classification and Morphology

Taxonomy

• Agnatha: Jawless fish (lampreys, hagfish).
• Chondrichthyes: Cartilaginous fish (sharks, rays).
• Osteichthyes: Bony fish.

Fins and Locomotion

• Caudal fin: Provides the main thrust for swimming.
• Dorsal and anal fins: Provide stabilization.
• Pectoral fins: Used for stabilizing, turning, and stopping.
• Caudal peduncle: The pivoting point of the caudal fin.
• Myomeres: Body musculature organized into distinct units.

Respiration and Sensory Organs

• Operculum: A large bony flap that covers the gills.
• Gills: Gill rakers provide support; gill arches prevent matter from clogging the blood; gill filaments allow oxygen to diffuse into the blood.
• Nostrils: Used for the olfactory sense; gill position is affected by feeding habits.

Reproduction and Development

• Fertilization: Most fish use external fertilization in aquatic plants or gravel stream bottoms.
• Strategies: Cod may lay 9 million eggs, while some sharks and rays exhibit internal fertilization, keeping young inside until they reach 40 cm.
• Live bearers: Guppies, mollies, and swordtails use internal fertilization to produce fully developed young.
• Parental care: Cichlids protect their young after hatching, often carrying them in their mouths.

Evolutionary History

Tetrapods (amphibians and reptiles) are related to sarcopterygians. Early groups include jawless fishes (hagfish, lampreys, ostracoderms) and jawed fishes (acanthodians).

Key Evolutionary Advancements

• Vertebral column: Replaced the notochord.
• Cranium: Protects the brain and spinal cord.
• Paired fins: Pectoral and pelvic fins supported by girdles of bone improved maneuverability.
• Buoyancy: Swim bladders and lungs resulted in refined buoyancy control.