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

•Shrimp shell meal (SSM) is good source of protein and natural astaxanthin for fish diet.•Dietary combination improves growth performance, health status and skin colouration.•Effective dose of synthetic and SSM mediated natural astaxanthin is 71.5 and 28.5 mg/kg in feed.•Study will be helpful in formulation of cost effective quality feed for ornamental fish.