First record of intraspecific cleaning behavior by the threatened Leuciscidae Squalius alburnoides (Steindachner, 1866) at the Guadiana River basin (Portugal).

Squalius alburnoides (Steindachner, 1866) is an endemic threatened species from the Iberian Peninsula. Here, we report the first observations of intraspecific cleaning behavior in isolated summer pools in the Guadiana River Basin (Portugal). We found that focal S. alburnoides solicited cleaning by adopting an immobile tail-stand position known as "posing," which immediately signaled a response to a few conspecifics that approached and inspect them. Our study expands the list of cleanerfish species in freshwaters, giving emphasis to the importance of mutual positive behavior within an endangered species, particularly when facing seasonal disturbance.