Spawning marks in spined loaches (Cobitis taenia, Cobitidae, Teleostei)

In Cobitis taenia and, with lower intensity, also in C. elongatoides and C. melanoleuca, females bear visible spawning marks on the body sides after spawning events. These marks intensify during the spawning season but disappear a few weeks after the last spawning event. The precise origin of the spawning marks is not clear, but they seem to be produced by the male during embracement of the female. Spawning marks were not observed after spawning events of C. bilineata, C. fahirae, C. rara, C. paludica, C. strumicae and C. turcica. An example dataset from Haaren creek in northwestern Germany is given to demonstrate that these marks can be used as a tool to precisely estimate the start of reproductive season for Cobitis populations, separately even for different size classes.