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Study shows impact of nitrate exposure on juvenile turbot intestinal health

New research shows that exposure to nitrates in recirculating aquaculture systems (RAS) in juvenile turbot induces intestinal inflammation. 

To evaluate the histopathological dynamic alterations of the intestine of turbot (Scophthalmus maximus) after exposure to nitrate, paraffin sections were observed and transmission electron microscopy (TEM) was conducted. 

The research by Jiachen Yu et al. shows that the intestinal tissue had a well-organized structure with orderly epithelial cells and an intact lamina propria – a type of connective tissue found under the thin layer of tissues covering a mucous membrane. 

For the study, juvenile turbot (body weight: 121.6 ± 12.7 g; body length: 18.5 ± 0.6 cm) were acquired and fed commercial pellets (0.5% of their body weight twice a day.)

Physicochemical parameters, including dissolved oxygen (7.9 ± 0.2 mg/L), temperature (15.2 ± 1.4 °C), pH (8.3 ± 0.2), salinity (18.8 ± 0.4‰), total ammonia nitrogen (0.17 ± 0.01 mg/L), and nitrite nitrogen (0.04 ± 0.02 mg/L), of the tanks were maintained. 

In the nitrate-exposed groups, all fish were exposed to a medium concentration of nitrate (200 mg/L NO3—N)

The fish were euthanized with tricaine methanesulfonate (MS-222), and intestine samples were gathered at 0, 10, 20, and 30 days, respectively. 

The structure of the intestine under nitrate stress exhibited different degrees of damage, including epithelial vacuolization, inflammatory cell infiltration, lysis in the lamina propria, microvillus fracture, and an increase in TJ gaps. These got more severe after prolonged exposure, especially after exposure to nitrate stress for 30days, the intestinal structure was loose.

“Our findings indicated that extensive tissue damage due to nitrate stress occurred in the intestine of turbot in a time-dependent way,” the research paper states.