So far, spawning grounds of most Antarctic fish species are not known. Nevertheless, there is a great deal of interest to locate these places and to protect them by international law. Rüdiger Riehl from the Institute of Zoomorpholgy, Cell Biology and Parasitology of the University of Duesseldorf might have found a way to do exactly that.

During his research on fish eggs, which spans over 30 years, he has found that most of these eggs possess microstructures that allow the identification of specimens to the family level, genus level and even species level. The tool of choice is a scanning electron microscope (SEM), which is used to capture minute differences on photographs. He is using differences in the microstructure of the egg surface, for example the presence or absence of ornamental patterns, distance and diameter of certain pores, and the appearance of the micropyle, the place on the surface of a fish egg where the spermatozoa penetrates the egg. The figures depict corresponding egg surfaces of the Patagonian Toothfish (Dissostichus eleginoides, above) and of an Antarctic Icefish (Chionodraco myersi, below).



But how is it supposed to work and give ecologically sound advice on resource management? In Antarctic waters, scientist frequently found unidentified fish eggs in plankton nets. These can now be identified with the help of scanning electron microscopy. Fish eggs are usually buoyant and therefore subjected to currents. By taking samples along this current and tracing back towards its place of origin the eggs should become less developed. Therefore the actual spawning ground worth protecting should be where the eggs are least developed.

Text and photographs: Rüdiger Riehl