Fishes chap 14

Swim Bladder and Buoyancy Control

Swim Bladder Functionality

• The swim bladder is a gas-filled organ that plays a crucial role in buoyancy control among fish. It allows fish to maintain their depth in the water column without expending energy. By adjusting the volume of gas in the swim bladder, fish can ascend or descend efficiently.

• The control over the swim bladder involves both hormonal regulation and neural mechanisms, where hormones, such as adrenalin and angiotensin, signal the bladder to inflate or deflate. Nerve innervations are also crucial, especially those affecting the gills and mouth, enabling precise control of buoyancy in various aquatic environments.

Structure of Swim Bladder

• Internally, the swim bladder is lined with guanine crystals, which contribute to its impermeability to gases. This structural adaptation ensures that oxygen is retained within the bladder, facilitating buoyancy.

• Fish can actively control their buoyancy by inflating or deflating the swim bladder depending on their behavioral needs, such as rising to the surface to feed or descending to avoid predators.

Species Variation

• In contrast to many fish, deep-sea fish often lack swim bladders, as buoyancy becomes less significant in their extreme environments. Instead, they may rely on other adaptations like reduced skeletal weight to manage buoyancy.

• Some species, like the anglerfish, exhibit specialized adaptations related to swim bladder functionality, allowing them to thrive in specific ecological niches, such as deep water or areas with strong currents.

Circulatory System of Fish

Heart Structure

• Fish typically possess a two-chambered heart, comprised of an atrium and a ventricle. This is unlike the four-chambered hearts found in mammals, reflecting the different physiological demands of aquatic life.

Blood Circulation

• The circulatory pattern in fish is generally organized in a singular circuit: blood flows in a clockwise direction, with deoxygenated blood returning to the heart after circulating through the body. The heart then pumps this blood to the gills for reoxygenation.

• Following oxygenation, the oxygen-rich blood is disseminated uniformly throughout the body, where oxygen is delivered to major organs and muscle groups, ensuring efficient metabolic processes.

Capillaries and Oxygen Delivery

• Capillaries are essential for the effective delivery of oxygen to tissues, especially in vital areas like the brain and caudal fin, where energy demands are particularly high.

Respiratory System

Gills for Respiration

• Fish gills are specialized structures that extract oxygen from water as it flows over them, facilitating respiration in aquatic environments.

Cartilaginous vs. Bony Fish

• Cartilaginous Fish (e.g., sharks): They require active movement of water through their open mouths and over the gills, a process known as ram ventilation, which is vital for their survival.

• Bony Fish have developed an operculum, a bony cover that creates a vacuum effect, allowing them to draw water over their gills actively for efficient oxygen extraction, enhancing their adaptability in various habitats.

Countercurrent Gas Exchange

• The mechanism of countercurrent gas exchange allows blood to flow through capillaries in the opposite direction to water flow, significantly enhancing oxygen absorption rates due to maintained concentration gradients.

• This highly efficient system allows fish to achieve remarkably high levels of oxygen saturation, vital for energy-intensive activities, such as swimming and hunting.

Osmoregulation in Fish

Definition

• Osmoregulation is the physiological process through which fish maintain their internal salt and water balance, adapting effectively to varying salinities in their aquatic environments.

Different Adaptations

• Cartilaginous Fish primarily take in salt through their diet and retain urea in their bodies, which helps to balance osmotic pressures in seawater.

• Bony Fish have a different approach: they actively drink water to replace lost fluids, excrete excess salt through specialized chloride cells in their gills, the gut, and urine while simultaneously retaining water to prevent dehydration.

Nervous System

Central Nervous System

• Fish possess a central nervous system consisting of a spinal cord and a brain. The structure of the brain generally varies significantly across different species, reflecting their ecological needs and behaviors.

Special Adaptations

• Certain areas of the fish brain may be enlarged due to specific ecological demands, such as enhanced vision in predatory species, which allows them to be more effective hunters.

• The Lateral Line System is a sensory organ that runs along the sides of fish, detecting vibrations and movements in the water, which is crucial for locating prey and avoiding predators.

Ampullae of Lorenzini in Sharks

• Ampullae of Lorenzini are specialized sensory organs found in sharks, enabling them to detect electrical fields generated by other organisms. This ability is essential for navigation and hunting, particularly in murky waters where visibility is low.

Differences between Cartilaginous and Bony Fish

Skeletal Structure

• Cartilaginous fish, such as sharks and rays, have skeletons made predominantly of flexible cartilage, which contributes to lighter body structures and buoyancy.

• In contrast, bony fish have rigid bony skeletons that provide greater structural support and leverage for muscle attachment, enhancing their swimming capabilities.

Reproductive Methods

• Cartilaginous fish often demonstrate viviparity (live births), which allows for greater parental investment and survival rates for offspring.

• Many bony fish, on the other hand, exhibit oviparity (egg-laying), where eggs are released into the environment, often resulting in larger brood sizes to ensure species survival.

Examples

• Most shark species are viviparous, offering unique reproductive advantages. Conversely, species like dogfish sharks and skates adopt oviparous strategies, highlighting the diversity of reproductive methods within the aquatic realm.

Skin and Scale Types

• Cartilaginous fish typically possess placoid scales, which give their skin a rough texture, thereby increasing drag during swimming but also aiding in streamlined movement as they adapt to their environments.