Laboratory of Benthos Ecology

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Sandra Casellato
Associate Professor - Aquatic Ecologist

Killer Shrimp. A Danger for Fish too!

When we think of predators, we tend to imagine them as rather large. It is difficult to think of a small shrimp, only 1-2 centimeters long, that lives in both fresh and brackish waters in over half of Europe, as an aggressive and voracious killer. The voracity of the "killer shrimp" is impressive. Fishermen, beware! In Lake Garda in Italy, this greedy killer has found even more succulent fare: fish eggs. Winter is a good season, because it is during this period that most lake fish spawn along the edges of the lake, and hordes of "killer shrimps" arrive for the banquet. The moment is also right for reproduction: many females of Dikerogammarus are carrying eggs at this time, and the future is bright for shrimp babies born in winter. It is less so for fish. In our laboratory, we set up “mesocosms”, in which we put a few individuals of Dikerogammarus with specimens of prey - isopods, other amphipods and plenty of whitefish eggs. We filmed our aggressive killer in action; within a few days, they had devoured the lot. Our report on killer shrimp in Lake Garda and the river Mincio came as a revelation, but we believe that this species is widespread in other large Italian Prealpine lakes likethe lakes Maggiore, Iseo and Como. It has already been found in Lakes Geneva and Constance and in the main European river basins. At the present time, in water used as ballast by cargo ships from Eastern Europe, other invasive species, like the mollusc Dreissena polymorpha and the amphipod Echinogammarus ischnus, have crossed the Atlantic and are worrying our North American colleagues. But the "killer shrimp" may well turn out to be the deadliest.

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