Dietary microalgal oligopeptides enhance growth performance, hepatic metabolism, immunity, and gut health in spotted seabass (Lateolabrax maculatus)

Aquaculture increasingly seeks functional feed additives to enhance productivity and sustainability. Microalgal oligopeptides (MOPs), recognized for their exceptional nutritional profile and bioactive properties, represent a promising candidate for this role. This study evaluated the effects of dietary MOPs supplementation on growth performance, hepatic metabolism, immune function, and gut health in spotted seabass ( Lateolabrax maculatus ). Fish were fed either a control diet (Con) or the control diet supplemented with MOPs at 250 (MOP250), 500 (MOP500), or 1000 (MOP1000) mg/kg. Compared to the Con group, the MOP500 group showed the highest weight gain and feeding rates with reduced hepatosomatic index ( P < 0.05). All MOPs-supplemented groups showed reduced hepatic lipid droplets, with the MOP500 group exhibiting lower levels of liver cholesterol than the Con group ( P < 0.05). Besides, the immunoglobulin M levels in MOPs groups, and lysozyme activity in MOP500 were significantly elevated ( P < 0.05). Further, decreased content of D-Lactate was found in the MOP500 group, as well as increases in intestinal villi length and lamina propria thickness, and upregulated of claudin-3 (P < 0.05). Of note, dietary MOPs downregulated gut il-1β and tnf-α expression ( P < 0.05), with the upregulated of pept1 . 16S rRNA sequencing further revealed that increased the abundance of probiotics and reduce the abundance of pathogenic bacteria. Collectively, 500 mg/kg MOPs enhanced the growth, immunity, lipid metabolism, and intestinal health of spotted seabass, demonstrating its potential as a beneficial functional additive in aquaculture. • MOPs increased weight gain rate and feeding rate. • MOPs improved liver health, lipid metabolism, and circulating cholesterol profiles. • MOPs strengthened intestinal health, barrier integrity, and inhibited inflammation. • MOPs enriched probiotics in the intestines and inhibit pathogenic bacteria.