# Sand Substrate Thickness Regulates Growth Performance, Intestinal Antioxidant Defense, and Gut Microbiota in an Experimental Culture of Marsupenaeus japonicus

## TL;DR

This study shows that a 10 cm sand layer in shrimp ponds improves growth, intestinal health, and survival in kuruma shrimp.

## Contribution

The study identifies 10 cm as the optimal sand thickness for kuruma shrimp farming, linking it to better intestinal health and microbial balance.

## Key findings

- Shrimp raised without sand had slower growth and higher intestinal damage.
- A 10 cm sand layer reduced oxidative stress and improved gut microbiota diversity.
- Very thick sand layers did not improve outcomes and may increase health risks.

## Abstract

Shrimp farming often uses artificial ponds, but it is unclear how much sand should be placed at the bottom to best support shrimp health and growth. This study tested four different sand thicknesses in a 120-day farming experiment with kuruma shrimp to determine which condition was most suitable. We found that shrimp raised without sand grew more slowly and had much lower survival rates. In contrast, shrimp raised on a sand layer 10 cm thick grew faster, survived better, and showed healthier intestines. These shrimps also experienced less damage caused by internal stress and had fewer damaged intestinal cells. In addition, the community of helpful microorganisms living in the shrimp intestine was richer and more balanced when a 10 cm sand layer was used, while the absence of sand reduced this diversity. Very thick sand layers did not provide additional benefits and may increase health risks. Overall, this study shows that using an appropriate sand thickness, especially 10 cm, can improve shrimp growth, intestinal health, and long-term survival. These findings provide practical guidance for shrimp farmers and can help make shrimp production healthier, more efficient, and more sustainable.

Kuruma shrimp (Marsupenaeus japonicus) exhibit natural sand-burrowing behavior, but the optimal sand substrate thickness for industrial farming remains unclear. This study evaluated the effects of different sand layer thicknesses on growth performance, intestinal health, oxidative status, and gut microbiota in Marsupenaeus japonicus. A 120-day controlled farming experiment was conducted using four sand substrate treatments: 0 cm (no sand), 5 cm, 10 cm, and 20 cm, with three replicate ponds per treatment. Growth indices, survival rate, intestinal histology, antioxidant enzyme activity, gene expression, and gut microbial composition were analyzed. Shrimp reared without sand showed markedly reduced growth and survival, increased intestinal damage, and higher oxidative stress. In contrast, shrimp cultured with a 10 cm sand layer exhibited improved growth and survival, lower intestinal oxidative damage and cell apoptosis, and healthier intestinal structure. This condition also supported a more diverse and stable intestinal microbial community and a lower abundance of opportunistic pathogenic bacteria compared with thinner or thicker sand layers. Overall, these results indicate that a sand substrate thickness of 10 cm provides the most favorable balance between growth, intestinal health, and microbial stability, offering practical guidance for optimizing kuruma shrimp aquaculture.