Fish meal substitution by meat and bone meal in large yellow croaker Larimichthys crocea diet: integrated insights on growth performance, intestinal morphology and microflora, antioxidant capacity, and protein metabolism

The present feeding study was carried out on Larimichthys crocea, with an initial weight of 18.36 ± 1.72 g, to assess the effects of substituting fish meal (FM) with meat and bone meal (MBM) on various factors, such as growth, intestinal morphology and microbiota, protein metabolism, and antioxidant ability. The five diets were created with varying percentages of FM replaced by MBM: 0% (MBM0), 25% (MBM25), 50% (MBM50), 75% (MBM75), and completely without FM (MBM100). The results exhibited that replacing 50% of dietary FM with MBM had no significant impact on fish growth or feed efficiency. An examination of intestinal morphology indicated notable reductions in villus width (VW), villus height (VH), and muscle thickness (MT) in the MBM75 and MBM100 groups. The MBM75 and MBM100 diets significantly reduced the activity levels of amylase (AMS), lipase (LPS), catalase (CAT), total superoxide dismutase (T-SOD), and total antioxidant capacity (T-AOC), while concurrently elevating the malondialdehyde (MDA) content considerably. 16S rRNA sequencing indicated that the MBM75 and MBM100 diets led to an elevation in the proportion of Proteobacteria and a reduction in the proportion of Firmicutes. Furthermore, immunoblotting analysis showed that in the muscle tissue, the MBM75 and MBM100 diets caused a notable reduction in the protein levels of 4E-BP1 (Thr37/46) and mTOR (Ser2448). Broken-line analysis revealed that the optimal substitution levels of meat and bone meal for fish meal were 40.60%, 50.00%, 42.08%, and 50.00% based on weight gain (WG), specific growth rate (SGR), feed conversion rate (FCR), and protein efficiency ratio (PER), respectively.