# Dietary Supplementation With Laminaria japonica Extract Modulates Microbial Metabolic Functions, Improving Growth Performance, Innate Immunity, and Antioxidant Capacity in Juvenile Procambarus clarkii (GIRARD, 1852)

## TL;DR

Adding Laminaria japonica extract to crayfish diets improves growth, immunity, and antioxidant levels by changing gut microbes.

## Contribution

The study identifies an optimal dose of Laminaria japonica extract that enhances crayfish health through microbial modulation.

## Key findings

- Laminaria japonica extract improved growth and hepatic health in crayfish.
- Supplementation increased antioxidant enzymes and immune activity in the hepatopancreas.
- The extract reduced harmful microbes and increased beneficial ones like Tyzzerella.

## Abstract

Concerns regarding food-borne interventions in crayfish have been raised due to excessive farming densities and the overuse of drugs in aquaculture. This research focused on examining the dose–response relationship of Laminaria japonica extract supplementation on growth performance, hepatopancreas antioxidant status, and innate immune function in crayfish, while exploring the microbiota-mediated metabolic pathways involved. A total of 750 juvenile crayfish (4.00 g) were randomly assigned to five treatments and fed diets supplemented with L. japonica extract at concentrations of 0, 500, 1000, 1500, and 2000 mg/kg for 42 days. The results demonstrated that dietary L. japonica extract improved the growth and hepatic health status, as indicated by well-structured hepatic tubules and increased fibroblast cells, as well as lower hemolymph glutamic oxaloacetic transaminase (GOT) level (p < 0.05). Dietary supplementation with 1500 mg/kg L. japonica extracts significantly increased hemolymph lysozyme (LZM) and acid phosphatase (ACP) activities (p < 0.05). Additionally, L. japonica extract supplementation considerably increased hepatopancreas glutathione (GSH) content and activities of catalase (CAT), superoxide dismutase (SOD), and GSH reductase (GR) (p < 0.05). Furthermore, dietary L. japonica extract alleviated microbial dysbiosis, as characterized by the observed decrease in opportunistic pathogens Citrobacter and Vibrio and an increase in beneficial taxa Tyzzerella. Further findings found that 349 differential microbes were identified, with Bacillus, Chryseobacterium, and Prevotella playing key roles. In summary, the optimal dietary inclusion level of L. japonica extract was recommended to be 1507.89–1614.26 mg/kg. Dietary supplementation with 1500 mg/kg of L. japonica extract improved the immunity and antioxidant capacities of crayfish by reshaping microbial co-occurrence networks.