Synergistic utilization of shrimp shell waste-derived natural astaxanthin with its commercial variant boosts physio metabolic responses and enhances colouration in discus (Symphysodon aequifasciatus)

This study investigated the effect of dietary supplemented synthetic, and shrimp shell meal (SSM) derived natural astaxanthin combination on growth, digestive and metabolic enzyme activities, antioxidative status, physio-metabolic responses, and skin colouration of high valued discus (Symphysodon aequifasciatus) advanced juveniles reared in captive condition. Four isonitrogenous (50 % crude protein), isolipidic (9% ether extract), and isocaloric (around 400 kcal digestible energy/100 g) experimental diets viz. Control (only synthetic astaxanthin, without SSM), T1 (15 % SSM + synthetic astaxanthin), T2 (20 % SSM + synthetic astaxanthin), T3 (25 % SSM + synthetic astaxanthin) were prepared and fed to satiation level twice daily for 90 days. Results indicated significantly (P < 0.05) higher weight gain percentage, FER, SGR, and PER and lower FCR in T2 and T3 groups compared to control. Combination effect of synthetic and natural astaxanthin significantly (P < 0.05) enhanced the protease activity, hematological parameters, and levels of serum immune parameters and decreased activities of amylase, hepatic and muscle MDH, LDH, ALT, AST with hepatic and gill SOD, CAT and serum glucose level with the most pronounced effects in T3 group. Significantly (P < 0.05) highest values of L*, a*, b*, chroma, and hue angle in the T3 group indicated their brightest skin colouration. Therefore, the study concluded that synthetic and SSM derived natural astaxanthin combinations at levels of 71.5 and 28.5 mg/kg, respectively, can be effectively supplemented in ornamental fish diets for improving their growth, health status, and skin colouration.