Effects of dietary ratio of n-3 to n-6 polyunsaturated fatty acids on growth performance, muscle quality, hepatic lipid metabolism, and intestinal health of rice field eel (Monopterus albus)

This study investigated the impacts of different dietary n-3:n-6 PUFA ratios on growth performance, muscle quality, hepatic lipid metabolism, and intestinal health in rice field eel (Monopterus albus ). Six diets with varying n-3 to n-6 PUFA ratios (LAP1: 0.51, LPA2: 0.9, LPA3: 1.43, LPA4: 3.36, LPA5: 4.25, and LPA6: 6.87) were prepared by adjusting the amounts of linoleic acid oil (n-6) and DHA+EPA oil (n-3). Juvenile M. albus (initial weight: 20.00 ± 0.01 g) were fed these diets for eight weeks. The results indicated that increasing n-3:n-6 PUFA ratio significantly enhanced weight gain rate, and specific growth rate, with a ratio of 3.36 (LPA4) group showing the best results. The muscle n-3 PUFA content was highest in the LPA4 group, while n-6 PUFA content decreased as the n-3:n-6 PUFA ratio increased. Furthermore, our results indicate that the dietary n-3:n-6 PUFA ratio influences the muscle fiber characteristics and muscle quality of M. albus . The myofiber diameter increased with the rise in the n-3:n-6 PUFA ratio, reaching the highest value in the LPA4 group. Muscle hardness and chewiness were improved in the LPA3-LPA6 groups. Increasing dietary n-3:n-6 PUFA ratio reduced hepatic lipid accumulation, inhibited the expression of lipid synthesis-related genes ( fas, g6pd, dgat2, lxra, srebp1 ), and promoted the expression of lipolysis-related ( cpt1, ppara, hsl, hl ) and lipid transport-related genes ( ldlr, mttp ). Liver antioxidant capacity initially increased but later declined as the n-3:n-6 PUFA ratio increased. Intestinal health improved in the LPA3-LPA6 groups, with increased goblet cell count, intestinal fold height, and muscle thickness, and higher tight junction-related gene expression ( claudin-15, claudin-12, zo-2, occludin-2 ). The expression of pro-inflammatory gene ( NF-kB1, tlr-8, il8, il1b, il15 ) significantly declined in these groups, while the anti-inflammatory genes ( il-10 ) were significantly upregulated. Intestinal trypsin activity increased significantly in the LPA2–LPA4 groups, peaking in the LPA3 group. Our study highlights that a dietary n-3:n-6 PUFA ratio of 1.43–3.36 enhances growth, improve muscle quality and intestinal health, and regulate liver lipid metabolism in M. albus . • Optimal dietary n-3:n-6 PUFA ratio significantly enhanced growth performance in rice field eel. • Dietary n-3:n-6 PUFA ratio influenced muscle fiber characteristics, muscle texture properties and fatty acid composition. • Optimal dietary n-3:n-6 PUFA ratio reduced hepatic lipid, enhanced antioxidant capacity, and improved liver lipid metabolism. • Appropriate dietary n-3:n-6 PUFA ratio improved rice field eel intestinal health, barrier function and modulated inflammation.