# Effects of Dietary Calcium and Magnesium Levels on the Growth Performance, Tissue Mineral Deposition, Exoskeleton Development, and Molting Performance of Chinese Mitten Crab (Eriocheir sinensis)

## TL;DR

This study examines how varying levels of dietary calcium and magnesium affect the growth and molting of Chinese mitten crabs.

## Contribution

The study reveals novel insights into the interactive effects of dietary calcium and magnesium on growth and exoskeleton development in crabs.

## Key findings

- Higher dietary calcium levels reduced weight gain and carapace hardness in crabs.
- Increased magnesium levels enhanced growth and exoskeleton development but suppressed chitin synthase gene expression.
- Interactive effects between calcium and magnesium levels were observed on molting performance and tissue mineral deposition.

## Abstract

Calcium and magnesium are essential mineral elements for animal growth and development, playing crucial roles in skeletal formation, particularly in the molting process of crustaceans. However, their interaction is still poorly elucidated. This study investigated the effects of dietary calcium and magnesium levels on the growth performance, tissue deposition of calcium and magnesium, exoskeleton development, and molting performance of Chinese mitten crab (Eriocheir sinensis). A 2 × 4 factorial design was adopted to formulate eight experimental diets, comprising two targeted calcium levels (1% and 2%) and four targeted magnesium levels (0.15%, 0.3%, 0.45%, and 0.6%). These diets were fed to crabs with an initial body weight of 40.46 ± 0.47 g for a 10‐week period. The results showed that increased dietary calcium levels significantly reduced the weight gain rate (WGR), hepatosomatic index (HSI), carapace hardness, tissue (hepatopancreas, intestine, and muscle) calcium content, the expressions of genes related to calcium and magnesium absorption in the hepatopancreas, and the expressions of genes associated with molting and exoskeleton development. In contrast, it decreased the levels of molting hormone in hemolymph, chitinase (CHI) activity in the epidermis, and the expressions of genes encoding the molting hormone receptor and CHI in the hepatopancreas. The highest WGR was observed at a magnesium level of 0.6%, which also significantly enhanced carapace hardness and methyl farnesoate (MF) content in hemolymph, but significantly suppressed the expressions of chitin synthase genes in the hepatopancreas. Moreover, at 1% calcium level groups, increased dietary magnesium levels significantly upregulated the expressions of magnesium absorption‐related genes. At 2% calcium level groups, with increasing dietary magnesium levels, the expressions of intestinal calcium absorption‐related genes initially decreased then increased, while those of hepatopancreas calcium absorption‐related genes significantly increased. Furthermore, significant interactive effects between dietary calcium and magnesium levels were observed on WGR, carapace hardness, collagen fiber content, CHI activity, and molting hormone levels in hemolymph. In conclusion, the interaction between dietary calcium and magnesium levels significantly influenced the growth performance, exoskeleton development, and molting of E. sinensis. An increase in dietary calcium levels should be accompanied by an appropriate elevation in magnesium levels in formulated feeds for this species.