Thursday, June 2, 2011

Raising larval cultures

In this Embryology class we raise embryos and larvae to gain a better understanding of how organisms develop. It is not hard to raise larvae, but it must be done with care. All of the species we work with are local marine invertebrates, collected either by us during the class field trips, or by our instructor ahead of time. The first step is to procure gametes, and the technique varies by species. Once we have fertilized eggs, we culture them in filtered sea water in clear glass custard bowls that hold 100-200 ml. The bowls are set in a sea table with flowing sea water, so the cultures are kept at ambient sea temperature. We label cultures using clothespins and colored tape (top picture).

Every other day the water must be exchanged using reverse filtration. A small plastic beaker with a mesh bottom (mesh size of 50-100 microns) is set in the culture bowl, and water is removed with a turkey baster, while the embryos or larvae remain in the bowl as you can see one of the students do in the middle picture. Bacteria and detritus go through the mesh together with the water. You must choose an appropriate mesh size so that the larvae are not going through it and make sure you leave a small amount of water on the bottom with larvae, so they are not crushed.

The next step is to transfer your larvae into a clean bowl and fill with filtered seawater. Some of our cultures need food to grow and develop. We have been feeding them a mixture of two kinds of unicellular algae, Rhodomonas lens (looks red) and Dunaliella tercioleta (looks green), which our teaching assistant grows in the lab in 0.5 liter glass flasks shown on the bottom picture.

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