# In Situ Recirculating Aquaculture System Improves the Growth Performance of Shrimp (Penaeus vannamei) via Shaping Diverse Bacterial Communities

## TL;DR

An in situ recirculating aquaculture system improves shrimp growth by enhancing water quality and promoting diverse beneficial bacteria in the gut and water.

## Contribution

This study reveals how IS-RAS shapes bacterial communities to enhance shrimp growth and water quality in aquaculture.

## Key findings

- IS-RAS improved water quality with reduced turbidity and nitrite levels.
- Shrimp in IS-RAS showed higher digestive enzyme activity and antioxidant capacity.
- Bacterial diversity and nitrogen metabolism genes were enriched in IS-RAS systems.

## Abstract

The in situ recirculating aquaculture system (IS-RAS) is regarded as an effective measure to reduce shrimp disease risks by minimizing exogenous water input and improving water quality. However, little is known about the effects of this system on bacterial communities in shrimp gut and rearing water. Here, the growth performance of shrimp and bacterial community characteristics in this culture system were assayed. The results show that the IS-RAS significantly improved rearing water quality, with a 2.2-fold reduction in turbidity, a 68.2% decrease in nitrite concentration, and enhanced hepatopancreatic digestive enzyme activities (e.g., amylase and lipase) and antioxidant capacities (e.g., superoxide dismutase and total antioxidant capacity). These improved physiological and biochemical indexes in the IS-RAS significantly increased the yield and survival rate, with increments of 23.5% and 25.9%, respectively, compared to that in CK. The IS-RAS significantly increased the bacterial diversity and enriched certain keystone taxa belonging to Roseobacteraceae, Paracoccaceae, Flavobacteriaceae, Nitrosomonadaceae, and Nitrospiraceae in both water and shrimp gut. These taxa play critical roles in maintaining bacterial network stability, and some of them were identified as potential taxa for promoting shrimp growth. Furthermore, the IS-RAS significantly upregulated functional genes associated with nitrogen metabolism (e.g., nirS, nirA, norB, napA, napB, and pmoA-amoA), thereby enhancing the nitrogen cycling potential of the bacterial community. These findings elucidate the biological mechanisms underlying IS-RAS-mediated improvements in shrimp farming productivity.