Lungfish Anatomy and Respiratory System

14 Questions

What is the primary function of the air-filled sacs in lungfishes and tetrapods?

Respiratory function

In which part of the esophagus does the trachea arise in the African lungfish?

Floor of the esophagus

What is the purpose of the faveoli in the lungs of the African lungfish?

To facilitate gas exchange with capillary blood

Why do most fishes tend to sink?

Because they are more dense than water

What is the significance of the high density of bone in bony fishes?

It makes them more dense

Why do almost all osteichthyans possess some form of gas bladder or lung?

To provide buoyancy and resist sinking

In which part of the body cavity is the single lung located in the Australian lungfish?

Dorsal position

What is the primary reason why actinopterygian fishes developed gas bladders?

To adapt to new environments and counteract sinking

What is the primary function of the swim bladder in fish?

To maintain buoyancy and compensate for the density of the fish body

What happens to the swim bladder when a fish descends to greater depths?

It compresses due to increased water pressure

How do fish with physostomous swim bladders adjust their buoyancy?

By gulping extra air or releasing spent air via the pneumatic duct

What is unique about the gas gland in some swim bladders?

It forms a countercurrent capillary arrangement with blood vessels

Why do fish need to add or remove gas from their swim bladder?

To maintain a constant volume and buoyancy

What type of swim bladder is characteristic of advanced teleost fishes?

Physoclistous

Study Notes

Evolution of Air-Filled Sacs in Fish

Air-filled sacs, such as lungs and swim bladders, arose early in bony-fish evolution and serve respiratory and hydrostatic functions.
In lungfishes and tetrapods, the respiratory function predominates.
In the Australian lungfish, the esophagus gives rise to a single lung in a dorsal position within the body cavity, which is also favorable to buoyancy control.

Lungs in Protopterus

In the African lungfish, Protopterus, the trachea arises from the floor of the esophagus and serves equally sized, paired lungs.
The lungs are subdivided into faveoli, where air forced into these lungs exchanges with capillary blood circulating in the walls of the faveoli.

Hydrostatic Function in Fish

In actinopterygian fishes, the hydrostatic function of air-filled sacs became more pronounced as they entered new adaptive zones of the marine environment.
Most fishes are denser than the water they live in, so they tend to sink, and the high density of bone in bony fishes makes this sinking tendency more pronounced.
Air-filled gas bladders give buoyancy to the fish body and help resist its tendency to sink.

Swim Bladders in Fish

Swim bladders are usually absent among bottom-dwelling bony fishes and fishes of open water that swim continuously.
In primitive teleosts, the swim bladder is physostomous, retaining its connection to the digestive tract via the pneumatic duct.
In most advanced teleost fishes, the swim bladder is a closed bag of gases called a physoclistous swim bladder.
Both types of swim bladders adjust the buoyancy of the fish to varying water depth.
The volume occupied by the swim bladder determines its buoyancy and its ability to compensate for the greater density of the fish body.

Buoyancy Control in Fish

Because water pressure increases with depth, the thin-walled swim bladder tends to be compressed when a fish descends and expanded when it rises.
Fish with physostomous swim bladders can add or remove gas by gulping extra air or releasing spent air via the pneumatic duct.
In some fish, gas secretion occurs directly across the walls of the bladder, while others have special gas glands from which gas from the blood is released into the bladder.