Evaluating the mixture of earthworm meal and wormcast as a protein source for common carp (Cyprinus carpio L.) based on growth performance, antioxidant, immune capacity, lipid metabolism and intestinal health

Abstract

This study was conducted to evaluate the effects of a dietary earthworm meal mixture (earthworm meal: EM and wormcast: WC) for replacing fish meal (FM) on growth performance, antioxidant capacity, lipid metabolism, and intestinal health of common carp (Cyprinus carpio L.). FM was used as the protein source in the control diet (D1), while 30% FM protein was replaced with an EM and WC mixture in the experimental diets, and the specific mixing ratio was as follows: D2 (15.4% EM), D3 (15.1% EM and 1.8% WC), D4 (14.8% EM and 3.7% WC), and D5 (14.5% EM and 5.8% WC). The growth performance was significantly decreased in the D4 and D5 groups compared with the D1 group, while the condition factor was highest in the D2 group (P < 0.05). In the antioxidant and immune respects, the expression levels of the sod and cat genes in hepatopancreas were remarkably upregulated in the D2, D3, and D4 groups (P < 0.05). Furthermore, serum lysozyme activities and lysozyme gene mRNA levels in head kidney reached the maximum in the D2 group. Additionally, the expression levels of interleukin 10 (il-10) and transforming growth factor β (tgf-β) in head kidney were enhanced in the D2 group (P < 0.05). For lipid metabolism, the expression levels in hepatopancreas of carnitine palmitoyl transferase 1 (cpt-1) were upregulated, while fatty acid synthase (fas) was significantly downregulated in the D4 and D5 groups (P < 0.05). In terms of intestinal health, dietary EM and WC increased the diversity and abundance of intestinal microbiota. The results showed no negative effect of the dietary earthworm meal mixture on growth performance after 30% FM protein was replaced by 15.4% EM or the 15.1% EM and 1.8% WC mixtures, which was beneficial for the health status of treated common carp.