BIOL-2116 - Cartilaginous Fishes Part 2 (13)

Cartilaginous Fishes Overview

• Reference: International Student Edition Animal Diversity, Cleveland P. Hickman, Jr. & co-authors, Ninth Edition.

Sensory Systems

• Vision Adaptations

  • Lens: Spherical, does not change shape, only position.

  • Light Conditions: Adapted to low light; high concentration of rods in retina.

  • Reflective Layer: Tapetum lucidum allows for internal light reflection, enhancing low-light vision.

• Mechanoreception

  • Function: Detects movements in water through a lateral line system.

  • Detection Mechanism: Senses displacements caused by vibrations in water via stereocilia (not actual hair).

  • Importance: Helps detect pressure changes and vibrations, crucial for navigation.

• Lateral Line System

  • Structure: Composed of canals with openings along the body.

  • Function: Water enters pores, contacting neuromast organs with clusters of hair cells, essential for detecting water movement.

• Electroreception

  • Capability: Detecting bioelectric fields from other animals through ampullae of Lorenzini.

  • Modification of the Lateral Line: Enhances prey detection capabilities through jelly-filled canals.

• Inner Ear

  • Sound Detection: Similar density to water, allowing sound waves to pass freely.

  • Frequency Range: Detects frequencies between 10-800 Hz.

  • Vestibular Apparatus: Contains semi-circular canals for motion detection in multiple planes.

Reproductive Characteristics

• Reproductive Strategies

  • Dioecious: Separate male and female reproductive organs.

  • Internal Fertilization: Distinct from the external fertilization common in many fish species.

  • Claspers: Male structures that assist in sperm transfer during mating.

• Oviparity

  • Prevalence: Utilized by 40% of sharks and all skates and chimaeras. Eggs are encased in protective "mermaid's purses."

  • Nourishment: Embryos receive nutrients through a yolk sac, developing over 6-10 months.

• Viviparity

  • Characteristics: Common in larger species; embryos retained within the reproductive tract.

  • Gestation: Duration varies between 1-2 years, with no post-birth parental care.

  • Types: Includes both ovoviviparity and placental viviparity.

Life History Traits

• Resource Allocation: Different strategies in terms of reproductive effort and frequency, ranging from low to high investment in offspring.

• Fast (r) vs. Slow (K) Life History Traits:

  • Fast Traits: Many small offspring, multiple reproductive episodes, quick maturation, shorter life span.

  • Slow Traits: Fewer large offspring, fewer reproductive events, delayed maturity, longer life span.

• Shark Examples: Greenland sharks (K-selected) mature slowly and have smaller litters.

Conservation Issues

• Vulnerability: Slow reproductive rates make sharks and rays susceptible to population declines, with an estimated 63-273 million killed each year for various resources (meat, fins, etc.).

• Finning Practices: Inhumane removal of fins leading to high mortality; many species now endangered.

• Canadian Legislative Measures: Shark finning banned in 1994, but imports were allowed until later efforts aimed to stop these imports.

  • Rob Stewart's Impact: His documentaries raised awareness about the importance of shark conservation.

• Shark Tourism: Economic benefits of keeping sharks alive; valuable shark ecotourism projected to double in growth the next decade.