Compound nucleotides as feed attractants improve the survival, growth, digestion, antioxidant capacity, and immunity of large yellow croaker (Larimichthys crocea) larvae

Abstract

The impact of dietary nucleotides (NTs) on the survival, growth, digestive enzymes, appetite-related genes, immunological response, and antioxidant capacity of large yellow croaker (Larimichthys crocea) larvae was assessed by a 30-day feeding study. Micro-diets with 0 % (control), 0.5 %, 1.0 %, or 2.0 % NTs were given to the larvae. The results showed that larvae fed 0.5 %, 1.0 % and 2.0 % NTs had remarkably higher specific growth and survival rates in contrast to the control group (P < 0.05). Trypsin and leucine-aminopeptidase activities in the intestinal segments were significantly elevated in NTs-fed groups (P < 0.05), while α-amylase activity in pancreatic and intestinal segments was reduced at 1.0 % NTs (P < 0.05). Antioxidant indicators, including total antioxidant capacity and catalase, were significantly enhanced with NTs supplementation, particularly at 2.0 % and 0.5 %, respectively (P < 0.05). Immune responses, such as lysozyme activity and nitric oxide content, also increased significantly in NTs-fed larvae (P < 0.05). Meanwhile, the pro-inflammatory genes (IL-6, IL-1β, COX-2) expression was significantly downregulated by NTs (P < 0.05), while appetite-stimulating genes like Neuropeptide Y and Ghrelin were upregulated, especially at 2.0 % NTs (P < 0.05). According to these results, the supplementation of 0.5 %-2.0 % NTs in the diet can enhance the antioxidant capacity, innate immunity, growth, survival, appetite, and digestive enzyme activity of large yellow croaker larvae, suggesting that NTs could be an effective feed attractant to enhance their health and growth performance.

Keywords: Appetite; Digestive enzymes; Immunological response; Inflammation; Larvae.