Impact of varying feeding levels on growth performance, body composition, digestive and metabolic enzyme activity, antioxidant defence, and health in olive barb (Systomus sarana)

This study assessed the effects of varying feeding levels per body weight on the growth performance, body composition, digestive and metabolic enzymes, antioxidant capacity, and innate immunity of fingerling Olive barb (Systomus sarana) under pond culture conditions. A total of 600 fish (6.7 ± 0.136 g) were distributed across 15 hapas (2 m × 1.5 m × 1.5 m) containing 40 fish per hapa and fed a diet (28% crude protein, 4% crude lipid) at five feeding levels: 0%, 1%, 3%, 5%, and 7% body weight per day (BW/day) for 90 days. Results showed that weight gain (WG: 9.5 g/fish), specific growth rate (SGR: 0.98%), and protein gain (PG: 1.5 g/fish) increased up to 3% BW/day and plateaued. Broken-line regression indicated breakpoints in WG and SGR at 3.67% and 3.23% BW/day, respectively. Maximum carcass protein and minimum moisture content were observed at 3% and 5% BW/day. Digestive enzyme activities, increased with feeding level. Polynomial regression indicated a breakpoint for protease at 3.82% BW/day. Antioxidant activity was highest at 5% BW/day, with a breakpoint in total antioxidant capacity (TAOC) at 4.46% BW/day. Superoxide dismutase (SOD) was highest at 1% BW/day, while catalase activity was similar at 1% and 3% BW/day. Metabolic enzyme activities varied, with maximum malate dehydrogenase (MDH) and glutamate dehydrogenase (GDH) at 3% BW/day, and glucose-6-phosphate dehydrogenase (G6PDH) peaking at 7% BW/day. GDH showed a breakpoint at 3.77% BW/day. Innate immunity analysis revealed higher respiratory burst and lysozyme activity at 3% BW/day, and haemoglobin content was highest at 1% BW/day. For optimal growth, a feeding level of 3.67% BW/day is recommended.