Among all the animals described by Hildegard of Bingen (a German benedictine abbess of the 12th century) in her scientific work Physica, fishes seem to be what she knew and observed best. According to many scholars, her "Book of fishes" might even be the most original contribution, in this field, to the whole medieval zoology. As a matter of fact, Hildegard's knowledge of aquatic fauna may be due to biographical, geographical and historical reasons : on one hand, she inhabited and founded cloisters situated on the river Rhine bank ; on the other hand, we know that fish played a great part in the diet of monasteries living under St. Benedict's Rule, which Hildegard herself commented in detail. We owe to her one of the oldest reports on Rhein...