Evaluating the effects of different levels of astaxanthin pigment on skin color and tissue texture of Parrotfish (Cichlasoma synspilum ♀ × Cichlasoma citrinellum ♂) using RGB and Lab techniques

Color is the most important characteristic of the ornamental fish. The use of pigments for changing the color of skin and carcasses has become more prominent in recent years. In the present study, the effects of astaxanthin pigment on skin color and tissue of parrotfish were studied using RGB and Lab techniques. Sixty parrotfish (with the average weight of 26.5±1.87 g) were distributed in different 50-liter volumetric aquariums (30×40×60 cm) and five dietary treatments with 3 replications for each treatment were considered. Treatments including the control (non-pigmented diet) and diets containing 0.2, 0.5, 1 and 1.5% of astaxanthin were prepared. After eight weeks of feeding fish with various treatments, four fish were taken from each treatment and their back muscles were used for the preparation of identical fillets. RGB and Lab techniques were used for the evaluation of the color of skin and muscle of fish. The results showed that change of color in the carcass texture in terms of the L component in all fish fed with the diets containing pigments were significantly decreased as compared to that of the control group (P<0.05). Change of color in the carcass texture in terms of the a component in all fish fed with the diets containing pigments except for the treatment containing 0.2% of astaxanthin were significantly increased as compared to that of the control group (P<0.05). Change of color in the carcass texture in terms of the b component in all fish fed with the diets containing pigments were significantly increased as compared to that of the control group (P<0.05). Change of color in the carcass texture in terms of the C_ab factor in all fish fed with the diets containing pigments except for the treatment containing 0.2% of astaxanthin were significantly different as compared to that of the control group (P<0.05). Change of color in the carcass texture in terms of the H_ab factor in all fish fed with the diets containing pigments were significantly decreased as compared to that of the control group (P<0.05). Data obtained from the skin color assessment using the RGB method indicated that the color of fish skin was dark at first and gradually with increasing the levels of astaxanthin it became brighter and finally it turned to orange-red color. Overall, the level of 0.5% of astaxanthin in parrotfish diet can be used to create red-orange color. Moreover, the results of the present study indicated the efficacy of RGB and Lab techniques in evaluating the color of fish skin and carcasses.