Freshwater Crab

Potamon fluviatile

The European freshwater crab (Potamon fluviatile) is a robust decapod crustacean reaching about 5 cm carapace width, found in rivers, streams, and lakes around the Mediterranean basin. Its carapace is dark olive-green to brown, broad and slightly flattened, with strong, slightly unequal chelae (claws) used for feeding and defense. Unlike most crabs, this species completes its entire life cycle in freshwater, with no marine larval stage. Females carry relatively large eggs and brood them under the abdomen, releasing fully formed miniature crabs rather than planktonic larvae. This species is primarily nocturnal, sheltering under rocks, in burrows along riverbanks, or among root systems during the day. It is omnivorous, feeding on detritus, aquatic plants, invertebrates, and small vertebrates. Freshwater divers in Mediterranean regions may find them in clean, well-oxygenated streams with rocky substrates, particularly at night when they are most active. The species is considered an indicator of good water quality and has declined in many areas due to pollution and habitat modification.