Effect of Nano- and Microparticulate Fermented Fish Protein Hydrolysate Diets on Growth, Digestive Function, Intestinal Development, and Gene Expression in Common Carp (Cyprinus carpio) Larvae

The early larval stage is a major bottleneck in freshwater aquaculture because conventional live feeds are not always available for optimum nutrient availability and digestibility to satisfy the nutritional requirements of developing larvae. This study evaluated the effects of micro- and nano-particulate fermented and fish protein hydrolysate-based diets on growth, digestive enzyme activity, intestinal morphology, and immune-related gene expression in common carp (Cyprinus carpio) larvae. Four experimental diets, namely fish hydrolysate-based micro-feed (FHMF), fermented micro-feed (FMF), fish hydrolysate-based nano-feed (FHNF), and fermented nano-feed (FNF), were compared with a basal diet. Feed characterization confirmed the successful production of micro- (5–15 µm) and nano-sized (90–105 nm) particles with distinct physicochemical properties. Three-day-old hatchlings were reared for 45 days, and growth performance, survival, digestive enzyme activities, intestinal histomorphology, and gene expression were analyzed. Diet type significantly influenced all measured parameters (p < 0.001). Among the treatments, FNF consistently produced the highest growth, survival, digestive enzyme activities, villus development, and muscular layer thickness. Growth-related genes (GH, IGF-1, and ghrelin) and immune-related genes (lysozyme, TNF, IL-1β, IL-10, and TGF-β) also followed an upregulated trend. These findings demonstrate that nanoparticulate fermented feed is a promising nutritional strategy for enhancing larval growth, digestion, immune competence, and production efficiency in common carp aquaculture.