Novel application of orange marigold flower petal (Tagetes erecta L.) as a dietary supplement to improve skin redness of Koi carps (Cyprinus carpio L.)

In this study, orange marigold (Tagetes erecta L.) petal was used as a direct lutein-containing resource for the Koi carps (Cyprinus carpio L.) with aim to enhance redness of specific area on their skin. The petals were collected from fresh orange marigold flowers, subsequenly dried at 50 oC and intensively ground into fine powder. Ultraviolet-visible (UV-vis) spectroscopy was performed for an ethyl acetate-mediated extract of the dried petal sample, showing the signature absorption peaks of lutein presented in the literature. Furthermore, a total carotenoid content of 6.57 mg/g was determined using a calibration curve of commerial lutein. Redness pigmentation of the selected Koi carps was performed via mixing the orange marigold petal powder with their daily food at two weight ratios of 5 and 20 gmarigold petal/kgtotal food, respectively, for a feeding period of six weeks. The photographs of the tested fish was recorded before and after this period and subsequently analyzed using a red-green-blue (RGB) system-based software to detect and compare possible variations in redness at the selected fish skin area. It was observed that the redness improvements of about 40% were obtained for all of the five fish fed with the food supplemented with the 20 g/kg ratio while using the 5 mg/kg ration was found to be inefficient. Importanly, the tested fish were in healthy conditions during the feeding period. These experimental results proved the great efficiency of orange marigold petal as an inexpensive and abundant agricultural alternative to costly imported carotenoid-containing feed for redness pigmentation of Koi carp in Vietnam.