IntroductionMosquitofish from The Bahamas, Gambusia hubbsi, and south Florida, Gambusia rhyzophorae, were observed to exhibit yellow‐orange coloration in their dorsal fins. Extracts from dorsal fins were analyzed by HPLC and a number of the pigments have been identified as carotenoids or carotenoid derived species.MethodsDorsal fins were extracted with hexane/acetone and the resulting solution concentrated under nitrogen. Extracts were analyzed by resolution in methanol/acetonitrile and chromatography using reversed phase C‐18 HPLC coupled with UV/visible detection at 450 nm was used to separate the components.ResultsAnalysis of extracts obtained from dorsal fins of 3–5 animals provided sufficient amounts of pigment for HPLC detection. Typical extracts are dominated by polar components and include lutein, epoxy carotenoids, and apo‐carotenals. In several samples a component was detected that exhibits a spectrum consistent with 3‐hydroxy‐10’‐apo‐carotenal.ConclusionPresence of 3‐hydroxy‐10’‐apo‐carotenal in the dorsal fins of mosquitofish appears to be consistent with CMO2 (carotenoid monooxygenase II) expression and carotenoid cleavage in the tissue. The function 3‐hydroxy‐10’‐apo‐carotenal may have in the fin is not immediately apparent but its unique presence suggests that it has an important role.