Question

1. a. Salt water is denser than fresh water. Which fish would need to have has a larger bladder? A saltwater or Freshwater bass?

b. What is fizzing a fish?

c. A shark is a cartilaginous fish that lacks an air bladder. If it can’t move, it will sink. Why?

d. How does the effect of water passing through a fishes gills affect his buoyancy?

e. Is the water moving past a gill and air passing over an airplane wing, the same or are they different? Why? Like all bony fish, a bass has a gas-filled sac or air bladder that allows it to float motionless below the surface of the water.

Answer 1

(a) Fresh water fish would need a larger bladder.

Since saltwater is denser than fresh water, we know that a given volume of salt water must have a greater mass than the same amount of fresh water. This means that a given volume of salt water weigh more than the same amount of freshwater. Since the buoyant force on the fish is equal to the weight of water that it displaces, we can conclude that the buoyant force exerted on the fish by the salt water is greater than the force exerted on the same-sized fish in freshwater. Since the buoyant force is larger in salt water and since the buoyant force is equal in magnitude to the weight of water that is displaced, the fish needs to displace a smaller volume of salt water to create the same buoyant force in fresh water. This means that the air bladder in a salt water fish is smaller than the air bladder in a fresh water fish.

(b) Fizzing a fish means to deflate the swim bladder of a fish caught in deep water.

(c) The purpose of an air bladder is to help a fish float by displacing relatively large amount of water, while at the same time weighing very little. Since sharks lack an air bladder, any buoyant force exerted on them depends only on the size of the shark. So for the shark to float, it needs to be less dense than water. As it turns out, sharks are denser than water, which means that the shark will not float. The shark must therefore rely on its swimming ability to keep it from sinking.

(d) The buoyancy of the water keeps the gill filaments apart.

(e) They are different because water moves through a gill and air passes over an airplane wing.