Reproductive behavior of endangered spined loach Cobitis magnostriata in the field

Spined loaches, Cobitis spp., have been studied in broad fields of research. Particularly, this taxon has attracted attention because of sexual interactions, such as reproductive interference and hybrid speciation, among species. Nevertheless, knowledge of the reproductive behaviors of this genus has been limited to findings from visual observations of aquarium-resident individuals. For this study, we shot videos and analyzed reproductive behaviors of Cobitis magnostriata in the field. We also investigated cues used by males to track females. Based on our observations conducted at a ditch near the shore of Lake Biwa during May-June, 2020, the sequence of courtship and spawning behaviors was divided into four phases: phase 1, a male tracks a female; phase 2, the male swims parallel to a female; phase 3, the male wraps the posterior part of the female's body from her dorsal fin and remains motionless; phase 4, after the male wraps the female tighter, the female vibrates to spawn. Additionally, we demonstrated that water vibrations initiate the male tracking behavior (phase 1). The adoption of such a non-species-specific cue might be one reason for which the sexual interspecific interactions have been widely reported in this genus.