Presence of an intrapineal circadian oscillator in the teleostean family poeciliidae

In most fish, rhythmic melatonin production is controlled by circadian osci llators located within the pineal (=pineal clocks) that are reset daily by the ambient light:dark (LD) cycle. However, one question that has yet to be addressed concerns the phylogenetic distribution of the pineal clock withi n fish families. We tested whether a pineal clock identified in the sailfin molly (Poecilia velifera) in an earlier study is also present in some othe r representatives of the teleostean family Poeciliidae; Isolated pineals fr om adults belonging to the genus Poscilia (P. velifera albino, I! reticulat a, and P. sphenops), genus Xiphophorus (X. helleri and X. maculatus), and g enus Limia (L. vittata)were obtained and cultured under LD and/or continuou s darkness (DD) at constant temperature (27 degrees C); With one exception, free-running rhythms in melatonin release with circadian periodicities ran ging from 19.5 to 27.4 h (n = 26) were detected in isolated pineals from al l paeciliid representatives tested under DD exposure. In addition, rhythmic melatonin production was also observed in isolated pineals of some represe ntatives tested from all three genera under LD exposure, suggesting the pro perty of direct photosensitivity. Taken together, these data suggest that a circadian oscillator residing in the pineal of the sailfin molly also appe ars to be: present: in all of the poeciliid representatives tested in our s ystem, supporting the notion that the presence of a pineal clock occurs at the family level of taxonomic organization. (C) 1999 Academic Press.