Abstract:
Generally, synthetic astaxanthin is used to maintain and enhance the skin colour of ornamental fish. However, it is expensive and causes an increase in the cost of production in aquaculture, as feed costs contribute significantly to the overall production expenses. Therefore, an alternative ingredient for skin coloration should be looked for to replace the high price of synthetic astaxanthin with a cheaper and locally available product. Koi fish (Cyprinus carpio koi) is one of the most popular ornamental fish, characterized by its beautiful body shape and vibrant colours, which give it high economic value. To get koi fish production with good colour quality, several supporting factors are needed, one of which is feed. In this study, hibiscus (Hibiscus rosa sinensis L.) powder was used as an additive in koi fish feed. The study was conducted using a completely randomised design with doses of hibiscus powder in the feed formulation as a source of anthocyanins, namely 0% (control), 2.5%, and 5%. Feeding was done two times a day with a feeding rate of 5%. Maintenance was carried out for 90 days, and observations of the colour brightness of koi fish were carried out once a week. The 5% hibiscus powder diet resulted in the highest feed efficiency (114.09%), carotenoid content (9.39 μg/g), and specific growth rate (2.09% per day), significantly outperforming the control diet in enhancing the growth, colouration, and feed utilisation of koi carp. As demonstrated by the higher relative percent survival in the 5% treatment group during the Aeromonas hydrophila challenge test, this finding further emphasizes the immunostimulatory qualities of hibiscus. For water quality parameters, temperature, pH, and dissolved oxygen levels are still within optimal limits for koi fish. This study supports hibiscus-based diets for improving coloration, growth, and disease control in koi carp, promoting eco-friendly and health-conscious practices in ornamental fish farming.
