1. Introduction to Sharks

Sharks are cartilaginous fish belonging to the class Chondrichthyes. They have existed for over 400 million years, making them one of the oldest surviving vertebrate groups. Sharks are found in all oceans and play a crucial role in marine ecosystems as apex predators.

2. Shark Anatomy

Skeleton

  • Made of cartilage, not bone.
  • Cartilage is lighter and more flexible than bone.
  • No ribs; their bodies are supported by muscles and skin.

Skin

  • Covered in dermal denticles (tiny, tooth-like scales).
  • Reduces drag and protects against parasites.
  • Gives sharks their rough, sandpaper-like texture.

Fins

  • Dorsal fin: stability.
  • Pectoral fins: steering and lift.
  • Caudal (tail) fin: propulsion.

Senses

  • Sight: Excellent vision, especially in dim light.
  • Smell: Can detect tiny amounts of blood in water.
  • Electroreception: Sense electrical fields via ampullae of Lorenzini.
  • Lateral line: Detects vibrations and movement.

Internal Organs

  • Liver: Large, filled with oil for buoyancy.
  • Stomach: Can expand greatly to accommodate large meals.
  • Spiral valve intestine: Increases nutrient absorption.

3. Shark Reproduction

  • Oviparous: Lay eggs (e.g., horn shark).
  • Viviparous: Give birth to live young (e.g., bull shark).
  • Ovoviviparous: Eggs hatch inside the mother (e.g., great white shark).
  • Some species show intrauterine cannibalism (siblings eat each other before birth).

4. Shark Diversity

  • Over 500 species.
  • Range from tiny dwarf lanternshark (about 8 inches) to whale shark (up to 40 feet).
  • Habitats: deep sea, coral reefs, open ocean, even rivers.

5. Shark Feeding and Behavior

  • Diet varies: fish, squid, crustaceans, marine mammals, plankton.
  • Hunting strategies: ambush, pursuit, filter feeding.
  • Social behavior: Some species are solitary; others form schools.

6. Mind Map

Shark Biology Mind Map

7. Surprising Facts

  1. Sharks can heal rapidly: Their skin contains compounds that speed up wound healing and resist infection.
  2. Some sharks glow in the dark: Species like the chain catshark use bioluminescence for camouflage and communication.
  3. Sharks have no swim bladder: Unlike most fish, sharks rely on their oily liver and constant movement to stay afloat.

8. CRISPR and Shark Genetics

CRISPR technology enables scientists to edit shark genes with high precision. This helps researchers:

  • Study genes responsible for cancer resistance (sharks rarely get cancer).
  • Investigate immune system adaptations.
  • Understand evolutionary history and develop conservation strategies.

9. Recent Research

A 2020 study published in Nature Ecology & Evolution mapped the genome of the white shark (Carcharodon carcharias) and found unique genes linked to DNA repair and immune function, which may explain their longevity and resistance to diseases (Marra et al., 2020).

10. Future Directions

  • Conservation Genetics: Using CRISPR and genome mapping to enhance shark conservation.
  • Biomedical Research: Studying shark immune systems for new medicines.
  • Environmental Monitoring: Tagging sharks with genetic markers to track populations.

11. Ethical Issues

  • Gene Editing: Should we alter shark genes for human benefit? Risks include unintended ecological consequences.
  • Conservation vs. Experimentation: Balancing research with respect for wild populations.
  • Animal Welfare: Ensuring humane treatment in genetic studies.

12. Shark Biology Diagram

Shark Anatomy Diagram

13. Summary Table

Feature Details
Skeleton Cartilage, flexible, lightweight
Skin Dermal denticles, tough, reduces drag
Senses Sight, smell, electroreception, lateral line
Reproduction Oviparous, viviparous, ovoviviparous
Feeding Diverse diets, unique hunting strategies
Genetics CRISPR enables precise gene editing
Conservation Genetic tools for population management
Ethical Issues Gene editing, animal welfare, ecological balance

14. Key Terms

  • Ampullae of Lorenzini: Sensory organs detecting electric fields.
  • Dermal Denticles: Tooth-like scales covering shark skin.
  • CRISPR: Gene-editing technology.
  • Cartilaginous Fish: Fish with skeletons made of cartilage.

15. References

  • Marra, N.J., et al. (2020). β€œWhite shark genome reveals ancient elasmobranch adaptations associated with wound healing and cancer suppression.” Nature Ecology & Evolution. Link
  • National Geographic Kids: Sharks. (2021).
  • NOAA Fisheries: Shark Biology. (2022).

End of Study Notes