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LAB 16 - Scanning Electron Microscopy of Gills
(Steelhead and Mussel)


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Scanning Electron Microscopy Of Steelhead and Muscle Gills
Fish have to swim but they have to breathe, too. Unlike land vertebrates or marine mammals, they don't have lungs, but they do have paired respiratory structures called gills. Gills are outgrowths of the body wall, and there purpose it to remove dissolved oxygen from water and expel carbon dioxide waste from the bloodstream. This is how fish can breathe underwater without ever having to come to the surface for air. When there are insufficient quantities of dissolved oxygen in the water, they will suffocate.

A big thing about respiratory organs is they pack a lot of surface area into a small volume. The purpose of this lab was for us to use the electron-scanning microscope (SEM) to take micrographs of steelhead gills and compare the structure of these fish gills with SEM micrographs of gills from the mussel (Mytilus californianus).

You can see here that the fish’s gills are feathery, which gives them a large surface area. The gills also come in several layers.

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This photomicrograph illustrates a section through a fish gill.    Click here for a larger version of this picture .

Surface Area =  (50.0Ám x 50.0Ám) x (1/16) x 2 x 20 = 6,250Ám

Here is a photomicrograph of a fish gill that I took myself, using the SEM during lab.

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Here are some photos of the gills of the mussel that were taken by a former student, Shaylin Hendrixson.

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Both the fish and the mussel use their gills for respiration. However, the way they pump water over their gills differs. In addition, fish use the gills for osmoregulation, and mussels use them for feeding, so one would expect these structures to be a bit different.

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Here is a picture of an electron-scanning microscope,
and a picture of the control panel on the SEM.

The scanning electron microscope is a microscope that uses electrons rather than light to form an image. The SEM has a large depth of field, which allows a large amount of the sample to be in focus at one time. The SEM also produces image of high resolution, which means that closely spaced features can be examined at a high magnification. For information on how the SEM works, click here.