More, Sagar Ravindra creator Krishna R. Salin Chairperson Yakupitiyage, Amararatne Examination Committee Bhujel, Ram C. Examination Committee Asian Institute of Technology Fellowship Scholarship Donor text th Pathum Thani, Thailand Asian Institute of Technology 2020 continuing eng 75 leaves : ill. One of the main factors on which the market value of the ornamental fishes depends are its colours. Enhancement of the colour of the fishes increases its market price. However, fishes cannot synthesize carotenoids by themselves and need to obtain them through their dietary intake. In this study, a popular aquarium fish, the Siamese fish (Betta splendens) was fed diets incorporated with varying levels of spirulina. Six diets were made as treatments; T0 with no supplementation of carotenoids, T1 with 20ppm astaxanthin, T2, T3, T4 and T5 with 30, 60, 90 and 120ppm spirulina respectively. The pigmentation of the fish skin was compared by doing the carotenoid analysis in the fish skin and the colour intensity by using the rapid image colour summarizer software. The skin of the fish fed with 120 ppm spirulina (T 5) had the highest carotenoid content (5.02æg/g±0.32) followed by the fish fed with 90 ppm spirulina,T4 (3.36 æg/g ±0.34). Other doses did not differ with control. Inclusion of spirulina significantly enhanced the color of the Siamese fighting fish at highest dose (120 ppm) but had no significant difference (P>0.05) in the growth rate during the experimental trial. Further, more extensive work with higher doses needs to be done to find out the optimum spirulina levels required to enhance the colour of the Siamese fighting fish. A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Aquaculture and Aquatic Resources Management Thesis (M. Sc.) - Asian Institute of Technology, 2020 Ornamental fish trade Siamese fighting fish Life cycles Aquaculture Nepal Asian Institute of Technology. http://203.159.5.9/ait-thesis/detail.php?q=B15908 http://203.159.5.9/ait-thesis/detail.php?q=B15908 220301 20260817173146.0