One of the most important parts of my research is doing microscopic analysis of the gonads. This allows me to assess what stage of maturation each fish was in at the time of its capture. A very common way of doing microscopic analysis is to use histology. Individual gonads are dehydrated (all the water in the cells are drawn out) by running them through a series of alcohol in increasing concentration. Once the water is pulled out of the cells, the gonads are infiltrated with hot paraffin wax which is poured into a mold. Once the wax is cooled, the wax block with the gonad embedded inside is sliced into very thin sections using a microtome. The microtome uses a very sharp knife to make slices of 5-7 μm, which is less than the diameter of a single human hair. The thin sections of gonad are then mounted on microscope slides, and stained with the dyes hematoxylin and eosin. These dyes have the effect of bringing out certain important components of the cells and making them visible under a light microscope. For example, I am interested in seeing whether the eggs have yolk globules in them, which would indicate that the fish was ripe.
The picture above is a cross section of oocytes (cell from which an egg or ovum develops) magnified at 10X.
Using a microtome to cut thin sections of tissue embedded in a paraffin wax block. The sections of wax stick together as they come off of the knife, and form “ribbons.”
Dyes used to stain sections of tissue after they have been sliced with a microtome and mounted on a microscope slide. The stains bring out certain important aspects of the cells so that they can be viewed easily under a microscope.