Preparations are fast taking shape for the construction of the controversial Nord Stream natural gas pipeline between Russia and Germany this spring. But it still faces a legal challenge in Germany from environmentalists, and critics say the project could disrupt the spring spawning of the herring found in the western Baltic Sea.

Preserved in formaldehyde and lying there in the stereo microscope's white light, the three fish larvae look like soybean sprouts. They're just one very small part of the spring-spawning herring found in the western Baltic Sea. In Germany, they are probably best known in the form they take much later: the tasty German snack known as Rollmops, a marinated herring fillet usually served rolled up around a pickle.

But these larvae are still far from meeting their maker. Measuring the larvae, which were caught about a year ago in very fine-meshed net, they are barely 10 millimeters long.

"Here you can already see the head, the eyes and fins," says Christian von Dorrien. The biologist works for the Von Thünen Institute for Baltic Sea Fishery in the old harbor in Rostock, a Baltic Sea port city in the German state of Mecklenberg-Western Pomerania. And while the water of the Warnow River estuary flows by the laboratory window, von Dorrien's colleague Dagmar Stephan is pre-occupied with lists of numbers, recording the size of fish larvae.