Corydoras arcuatus is a species of freshwater fish in the armored catfish family Callichthyidae. It is restricted to the western Amazon basin, where only known from small blackwater or clearwater streams in the middle Juruá River basin, the Javari River basin and streams near Leticia in western Brazil, far northeastern Peru and far southeastern Colombia.[1]
The separation of C. arcuatus and C. granti was only fully clarified in 2019; information published for "C. arcuatus" before this was almost invariably for C. granti.[1] Similarly, the common name skunk corydoras has often been used for C. arcuatus, but the vast majority of skunk corydoras in the aquarium trade are actually C. granti (leading several authorities to transfer the common name skunk corydoras to C. granti).[1] [2] [3] The two species are very similar and locally they occur together, with both being restricted to the western Amazon basin, but C. granti is more widespread.[1] [2] [3] In addition to these two, a few other Corydoras species (for example, C. bethanae, C. narcissus and C. urucu) from the western Amazon basin have similar color patterns, as does Brachyrhamdia thayeria; they all have spiny fins with a (to humans) painful but not dangerous venom and their similarity is an example of Müllerian mimicry.[1] [4] [5]