Study shows how nitrates in RAS systems affect fish health

Turbot, scophthalmus maximus, Adult swimming

Exposure to nitrates can adversely affect the intestinal health of fish in RAS systems, a study by researchers in China has found.

While it is well known that nitrates have a toxic effect, the study provides a detailed analysis of how nitrate (NO3) levels can have an impact at molecular level.

A team of scientists at the Jiangsu Key Laboratory of Marine Biology, on China’s east coast, studied the effect of nitrate stress on juvenile turbot in a RAS (recirculating aquaculture system) environment.

They found that exposure to nitrates caused intestinal histopathological damage and inflammatory response. The intestine acts as an important barrier against bacteria and toxins, so when it is weakened it increases the risk of range of health issues.

The study also applied “transcriptomic” analysis, an approach which analyses the “transcriptome”, the compete set or ribonucleic acid (RNA) molecules in a cell or organism. It found that exposure to higher levels of nitrate affected the intestine at molecular level in four important ways, described as “pathways”, adding up to a damaging impact on health.

Six “hub” genes identified in the fish were shown to play a vital role in the response of turbot to nitrate toxicity, influencing the degree to which they were able to resist the effects of nitrate.

Nitrates can easily build up in RAS systems and can be hard to detect. While the link between nitrate levels and fish health is well known, the research has pinpointed the precise mechanism by which nitrate exposure affects intestinal functions.

The scientists said: “Our findings may offer valuable information on the molecular mechanisms of the response of fish to nitrate stress and also may contribute to the welfare of fish in RAS.”

Exposure to nitrate induces intestinal inflammation, as determined by an integrated transcriptome and weighted gene co-expression network analysis in juvenile turbot (Scophthalmus maximus), Aquaculture March 2024

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