The jewelled splitfin fish do not use UV wavelengths for intraspecific signalling

Abstract The jewelled splitfin fish Xenotoca variata have speckles, made up of iridescent scales with UV reflectance as an important component. The males of this freshwater viviparous species develop a greater number of speckles than females. Previous work has found that the speckles play a role in both mate choice and agonistic interactions. Females presented with two males often prefer the male with more speckles. Speckled males tend to deter rival males with fewer speckles while displaying courtship behaviour to females. Given that the UV components of colour patterns are known to play key signalling roles in behavioural interactions across taxa, we wanted to determine if these fish could see UV light and if they used UV reflectance of the speckles in their interactions with conspecifics. Besides the rods, we identified two types of single cones (λmax at 412 and λmax at 490 nm) and one type of double cone (λmax at 620 nm). By comparing the males and females’s behaviour when allowed to assess conspecifics with and without UV light, we found that the experimental fish exhibited similar behaviours toward the stimuli fish. However, females showed increased visit frequency and spent more time near males with a higher number of speckles. The absence of behavioural response to UV treatment aligns with the lack of UV sensitive cones, suggesting that iridescence-associated UV wavelengths may not play a direct role in intraspecific social interactions.