Name: ______Date: ______Per:______

WS 5.5 - Perch Dissection Day 2

Procedure:

  1. Obtain a perch and place the perch in your dissecting pan.
  2. Find the bony covering of the gills on each side of the fish's body called the operculum.
  3. Use scissors to cut away one operculum to view the gills. Find the gill slits (spaces between the gills)
  4. Use scissors to carefully cut out one gill.
  5. Cut apart a gill separating the gill filaments from the gill arch and put each on the correct circle

Below is a picture of perch gills. Label the Gill Arch, and Gill Filaments, and Gill Rakers

Questions:

  1. What type of fish has an active repertory system (meaning the fish can pass water over its gills without moving)
  1. What type of fish has a passive repertory system (meaning the fish cannot pass water over its gills without] moving)
  1. What are the function of gill Rakers?
  1. Why don’t we need lung rakers? (Hint: what can we do to clean out lungs)
  1. Why would fish that suspension feed have larger gill rakers?
  1. What are 2 external features that separate a boney fish’s repertory system from a cartilaginous fish’s repertory system?

  1. Read the following

Oxygen dissolved in the water diffuses into the capillaries of the gill filaments to oxygenate the blood. Diffusion will take place only if oxygen is more concentrated in the water than in the blood. This is usually true because the blood coming to the gills has already traveled through the rest of the body and is depleted of oxygen. As oxygen diffuses from the water into the blood, the concentration of oxygenin the water decreases as the concentration of oxygen in the blood increases. This can reduce the efficiency of gas exchange, which depends on the water having more oxygen than the blood. For this reason, fishes, have evolved a countercurrent system of flow to increase breathing (gas exchange) efficiency. A countercurrent system of flow means the blood in the gills flows in the opposite direction to the water passing over them. When the water has passed over the gill and given up much of its oxygen it meets blood that has just come from the body and is most hungry for what oxygenremains in the water. By the time the blood has flowed most of the way through the gill, it encounters water that has just entered the gill chamber and is rich in oxygen. This countercurrent system of flow means that the oxygenconcentration in water is always higher than the oxygen concentration in the blood, and thus this system means oxygen will always diffuse into a fishes gills.

  1. Circle the picture that demonstrates countercurrent system of flow:

  1. Why don’t humans or any air breathing animal need a countercurrent system of flow in our circulatory system?
  1. Compare and contrast the perch’s mouth and teeth with the dogfish’s mouth and teeth. Match the food to the mouth(s) that is most adapted to eat it:
  2. Algae and PlanktonPerchDogfishBoth
  3. Aquatic InsectsPerchDogfishBoth
  4. Small FishPerchDogfishBoth
  5. Medium FishPerchDogfishBoth
  6. Large Fish PerchDogfishBoth
  7. Lobster and Large CrabsPerchDogfishBoth