Adding moderate amounts of biochar made from discarded mulberry branches to fish feed may offer a practical way to support intestinal health and reduce harmful nitrogen compounds in aquaculture water, according to a new study in largemouth bass.
Researchers found that dietary mulberry branch biochar improved digestive enzyme activity, strengthened indicators of intestinal barrier and antioxidant function, increased gut microbial richness, and reduced potentially harmful bacteria. At appropriate doses, it also substantially lowered ammonia nitrogen and nitrite nitrogen in the surrounding water, without negatively affecting fish growth.
"Our findings show that mulberry branch biochar can play two beneficial roles at the same time: supporting the intestinal environment of fish and helping maintain cleaner aquaculture water," said corresponding author Hailong Wang. "This approach could transform an agricultural residue into a functional feed ingredient for more sustainable fish production."
Largemouth bass is an economically important freshwater species, particularly in China. However, intensive aquaculture can produce large quantities of uneaten feed, feces, and other organic waste. As these materials decompose, ammonia and nitrite can accumulate in the water, affecting fish appetite, health, and survival.
To investigate whether biochar could help address these challenges, the researchers produced biochar from mulberry branches by heating the biomass at 550 °C under oxygen-limited conditions. Mulberry trees are commonly planted near fish ponds in southern China, making their discarded branches a locally available feedstock.
A total of 480 juvenile largemouth bass were assigned to diets containing 0, 10, 20, or 40 grams of biochar per kilogram of feed. The fish were raised for 42 days in independent recirculating aquaculture systems.
The biochar supplements did not significantly change final body weight, weight gain, survival, or feed conversion. However, the fish receiving 20 or 40 grams of biochar per kilogram of feed showed significantly greater intestinal trypsin and amylase activity, suggesting an improved capacity to digest proteins and carbohydrates.
At lower and moderate inclusion levels, the biochar also affected genes related to intestinal protection. Fish receiving 10 or 20 grams per kilogram showed increased expression of the antioxidant gene sod and the tight-junction gene Occludin. The 10-gram treatment additionally increased expression of the anti-inflammatory gene IL-10.
Biochar supplementation significantly increased the richness of intestinal bacterial communities. It also altered the overall microbial composition, including an enrichment of Actinobacteriota, a group associated with nutrient metabolism and immune regulation. The relative abundance of potentially pathogenic genera, including Plesiomonas and Mycoplasma, declined in biochar-fed fish.
Water-quality improvements were especially notable at moderate doses. By day 42, diets containing 10 and 20 grams of biochar per kilogram reduced ammonia nitrogen by 60.7% and 49.3%, respectively, compared with the control. Nitrite nitrogen was also lower, with the 10-gram treatment producing a reduction of 91.78% at the end of the trial. Total nitrogen, however, was not significantly affected.
The highest dose did not provide the best overall outcome. Fish receiving 40 grams per kilogram showed a lower condition factor, increased expression of the inflammatory gene TNF-α, and greater variation in gut microbial communities. These findings indicate that excessive biochar may adsorb nutrients or disturb intestinal balance.
Overall, the researchers identified 10 to 20 grams of mulberry branch biochar per kilogram of feed as the most promising range for improving intestinal function and water quality. The study highlights a circular approach that converts agricultural waste into a potentially valuable tool for cleaner and healthier aquaculture.
The study was published in Biochar X.
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Journal reference: Chen B, Hu J, Peng K, Huang W, Li J, et al. 2026. Dietary mulberry branch biochar improves intestinal health and water quality in largemouth bass (Micropterus salmoides) aquaculture. Biochar X 2: e014 doi: 10.48130/bchax-0026-0010
https://www.maxapress.com/article/doi/10.48130/bchax-0026-0010
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About the Journal:
Biochar X (e-ISSN: 3070-1686) is an open access, online-only journal aims to transcend traditional disciplinary boundaries by providing a multidisciplinary platform for the exchange of cutting-edge research in both fundamental and applied aspects of biochar. The journal is dedicated to supporting the global biochar research community by offering an innovative, efficient, and professional outlet for sharing new findings and perspectives. Its core focus lies in the discovery of novel insights and the development of emerging applications in the rapidly growing field of biochar science.
