# Effect of Coated Inorganic Micro-Minerals on Growth, Mineral Retention, and Intestinal Health in Juvenile American Eels Under a Commercial RAS

## TL;DR

Coated inorganic micro-minerals improve growth and intestinal health of juvenile American eels in commercial aquaculture systems compared to traditional minerals.

## Contribution

Demonstrates that coated inorganic micro-minerals are more effective than traditional ones in commercial RAS conditions for juvenile American eels.

## Key findings

- Coated inorganic micro-minerals significantly improved growth and mineral retention in juvenile American eels.
- CIMM enhanced intestinal health through better enzyme activity, antioxidant capacity, and microbiota composition.
- A 500 mg/kg CIMM dose was insufficient in commercial conditions, suggesting higher mineral requirements than in lab settings.

## Abstract

Traditional inorganic micro-minerals can damage nutrients in fish feed and are poorly absorbed by fish. If these minerals are coated with a protective layer, their reaction with feed nutrients during the fish’s digestion can be reduced. This helps solve the above-mentioned problems and promotes fish growth and health. This study was conducted in a commercial recirculating aquaculture system (RAS) to test the effects of adding traditional vs. coated inorganic micro-minerals to feed on juvenile American eels. The assessment focused on their growth, body composition, mineral absorption, and intestinal health. The results showed that coated inorganic micro-minerals performed much better than traditional ones in all these aspects (i.e., growth and intestinal health), so using such coated micro-minerals in commercial culture conditions can significantly benefit juvenile American eels.

Micro-minerals are essential for fish, but traditional inorganic micro-minerals (IMM) have low bioavailability. This study evaluated coated inorganic micro-minerals (CIMM) in juvenile American eels under commercial recirculating aquaculture system (RAS) conditions. Three experimental groups (n = 3 tanks per group, stocking density: 138 fish/m3) were fed basal diets supplemented for 56 days with: 1000 mg/kg IMM (IMM group, providing Cu 7, Fe 200, Mn 30, Zn 70, I 1.6, Se 0.4, and Co 1.2 mg/kg diet), 1000 mg/kg CIMM (CIMM group I), or 500 mg/kg CIMM (CIMM group II). Compared to the IMM group, the CIMM group I demonstrated significantly enhanced growth performance, with the specific growth rate increasing by approximately 31.14%, higher whole-body content and retention of minerals (Ca, P, Cu, Fe, Mn, Zn), and superior intestinal health, as reflected by significantly increased activities of digestive enzymes (amylase and lipase), enhanced antioxidant capacity (elevated SOD and CAT, reduced MDA), and improved morphology (villi length and muscular thickness), an altered intestinal microbiota (increased relative abundance of Firmicutes and reduced relative abundance of Proteobacteria), and significant metabolomic alterations in purine metabolism and linoleic acid metabolism. The CIMM group II maintained growth performance, with no significant difference in WGR and SGR compared to the IMM group, while still showing significant improvements in feed intake and mineral retention (P, Cu, Fe, Zn), and antioxidant capacity. Collectively, this study not only confirms the efficacy of CIMM in commercial RAS but also reveals that the supplementation level previously shown to be effective in the laboratory (50% CIMM) is insufficient under commercial farming conditions, implying that the dietary micro-mineral requirements for juvenile American eels in commercial RAS may be higher than those established in laboratory settings.