Combined Effects of Dietary Soybean Lecithin With Vitamin C or Inositol on Growth, Gonadal Development, and Intestinal Microbiota in Longsnout Catfish

To investigate the combined effects of soybean lecithin (SL) with vitamin C (VC) or inositol (INO) on growth, gonadal development, and intestinal microbiota, 2-year-old longsnout catfish (Leiocassis longirostris) were fed four isonitrogenous and isolipidic diets for 12 weeks, including a control diet, a 4% SL diet, a 4% SL + 0.5% VC (SC) diet, and a 4% SL + 0.5% INO (SI) diet. A two-way analysis of variance (ANOVA) revealed a significant diet × sex interaction for weight gain rate (WGR) and specific growth rate (SGR) (p < 0.05). In females, the SI group exhibited the highest WGR and SGR, while both the SC and SI groups showed significantly higher WGR and SGR than both the SL and control groups in males (p < 0.05). All three supplemented groups promoted gonadal development, as reflected by higher gonadosomatic index (GSI) and elevated serum 17β-estradiol (E2) and progesterone (P4) levels. Both SC and SI groups showed significantly increased total antioxidant capacity (T-AOC), superoxide dismutase (SOD), catalase (CAT), and alkaline phosphatase (AKP) activities and significantly decreased malondialdehyde (MDA) and cortisol levels compared with the control group (p < 0.05). Dietary SC enriched potentially beneficial Bacteroides in both sexes. SI enriched potentially beneficial Cetobacterium in males. Furthermore, all three supplemented diets reduced the potentially pathogenic Plesiomonas in females. Gonadal transcriptome analysis suggested that SL combined with VC or INO may modulate pathways such as the peroxisome proliferator-activated receptor (PPAR) signaling pathway, biosynthesis of unsaturated fatty acids, estrogen signaling, and histidine metabolism, implying potential roles in gonadal lipid metabolism, chaperone-mediated protection, and immune homeostasis. Overall, SI was most effective in promoting growth in females, whereas both SC and SI were more effective in promoting gonadal maturation, enhancing antioxidant capacity, and improving intestinal microbiota composition. This study provides theoretical guidance for the development of specialized compound feeds during the gonadal development period in longsnout catfish aquaculture.