Bioaccumulation of stentorin, the probable causative agent for discolored (“purple”) eggs and ovaries in blue catfish (Ictalurus furcatus) from Eufaula Lake, Oklahoma, USA

Observations of reddish to “purple” discolored eggs in the ovaries of adult female blue catfish (Ictalurus furcatus) from the northern arm of Eufaula Lake, a eutrophic multiuse impoundment in east-central Oklahoma, were first reported in 2006. Blue catfish eggs are normally cream to light yellow. Reports peaked in 2007–2008 and declined through 2009–2010; purple eggs have not been reported between 2010 and 2014. In the laboratory, all tissues and fluids of affected fish were strongly orange-red fluorescent under UV illumination, with the fluorescence most apparent in the lipid-rich ovaries and eggs. The causative agent was isolated chromatographically and confirmed by mass spectrometry as stentorin (1,3,4,6,8,10,11,13-octahydroxy-2,5-diisopropyl-phenanthro[1,10,9,8,o,p,q,r,a]perylene-7,14-dione), the fluorescent, lipophilic pigment associated with the photoreceptor protein of the ciliated protozoan Stentor coeruleus (Heterotrichea; Stentoridae). Larval medaka (Orizias latipes) readily consumed S. coeruleus in the laboratory and were observed to fluoresce in the same manner as the affected blue catfish. Potential deleterious effects of stentorin bioaccumulation remain to be determined, as do the geographic extent and the identities of other fluorescent compounds isolated from catfish eggs and ovaries.