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Farmed fish are increasingly replacing wild fish to meet consumer demand in China, as well as Australia—and barramundi is a popular choice.

Aquaculture research led by Flinders University and experts in China continues to examine the benefits—and possible side effects—of improving fishmeal for farmed fish, with a new study investigating the potential of herbal additives to improve fish immunity in more sustainable future production systems.

The study, has been published in Ecological Indicators

The increasing global demand for sustainable and antibiotic-free aquaculture has prompted the exploration of natural plant extracts as alternatives to traditional chemical additives, particularly antibiotics, in improving fish immunity, says Flinders University Professor of Aquaculture Jian Qin.

"Some of the herbal additives in this study benefited the biochemical and immune responses in juvenile barramundi, at a stage when they are more susceptible to disease or infections," says Professor Qin, from the College of Science and Engineering at Flinders University.

Collaborator Professor Zhenhua Ma, director of the Tropical Fisheries Research and Development Center at the South China Sea Fisheries Research Institute, adds, "While these results indicate that some plant extracts tested could be beneficial additives in aquaculture feed, their potential risk to other environmental organisms should be further investigated before their extensive application in aquaculture."

Testing led by Flinders Ph.D. candidate Ms Zhengyi Fu, who is based at the Sanya Tropical Fisheries Research Institute in Hainan Province and the Chinese Academy of Fishery Sciences in Guangzhou, sought to assess the environmental toxicity of the plant extracts in various marine environments.

The ecotoxicity and physiological impacts of four plant extracts—gallnuts (Rhus chinensis), green chiretta (Andrographis paniculata), white mustard (Sinapis alba), and betel nut (Areca catechu)—were tested on juvenile barramundi (Lates calcarifer) as well as three other marine species including brine shrimps (Artemia salina).

While plant-based additives are generally safe, some bioactive compounds within these extracts have demonstrated potential toxicity, raising concerns about their environmental and ecological impacts.

Along with the potent antibacterial and antiparasitic properties of the four herbs tested, there was a focus on bioactive compounds within them, such as phenols, terpenoids, alkaloids and organosulfides, which may affect aquatic ecosystems, according to the article.