The chronic effect of nitrate on production performance and health status of juvenile turbot (Psetta maxima)

The chronic effect of nitrate on the production performance and health of marine cultured fish species is still unknown. Thus, the aim of the present research was to evaluate the chronic effect of nitrate on production parameters and health status of turbot (Psetta maxima). Juvenile turbot were exposed to 0 mg/L NO3–N (control C), 125 mg/L NO3–N (low nitrate LN), 250 mg/L NO3–N (medium nitrate MN) and 500 mg/L NO3–N (high nitrate HN) for 6 weeks in small-scaled recirculating aquaculture systems (RAS). After 42 d, biomass yield, length, weight and specific growth rate (SGR) were significantly (p < 0.05) lower for LN, MN and HN compared to C. Mortality, food conversion ratio (FCR), condition factor (CF) and splenic index (SI) did not differ significantly (p > 0.05) between C and LN but were significantly (p < 0.05) higher in the MN and HN groups. Hepatosomatic index (HSI), total hemoglobin (Hb) and methemoglobin (MetHb) did not show significant differences (p > 0.05) between treatments. Thus, nitrate negatively influences the production performance of turbot, even at low concentrations and nitrate management is therefore a key-factor in turbot RAS production.

► Turbot health, growth and feed utilization are correlated with nitrate levels.
► Turbot growth is affected ≥125 mg/L NO3–N.
► Turbot physiology is affected ≥250 mg/L NO3–N.
► Turbot are capable of keeping homeostasis up to 500 mg/L NO3–N.