The effect of nitrite and nitrate treatment on growth performance, nutritional composition and flavor-associated metabolites of grass carp (Ctenopharyngodon idella)

Abstract

Water quality is closely related to the nutritional and sensory qualities of grass carp, which has the largest aquaculture production among freshwater fishes. The purpose of this study was to explore the effects of nitrite and nitrate on the growth performance, nutrition composition and muscle flavor-associated metabolites of grass carp through an exposure experiment with varying concentrations (nitrite 0.1–1 mg/L, nitrate 2–8 mg/L). Nitrite at 0.5–1 mg/L and nitrate at 2–8 mg/L significantly reduced the growth performance [e.g., ∼20 points reduction in weight gain (%), P < 0.05]. Nitrite and nitrate treatments significantly decreased crude protein, crude fat, carbohydrate content and amino acid content in muscle at most concentrations tested with significant concomitant increases in the water content. Grass carp treated with 1 mg/L nitrite had the highest concentrations of geosmin (GSM) and 2-MIB (∼4–6 μg/kg compared to the ∼0.5–1 μg/kg in the control group, P < 0.05). The metabolomic analysis showed that both nitrite and nitrate affected flavor-associated metabolites, and nitrite treatment produced more differential metabolites than nitrate treatment. Nitrite treatment mainly affected amino acid metabolism and protein digestion and absorption pathways; specifically, the synthesis of arginine and the metabolic pathways of glutamic acid and proline were significantly down-regulated. This study provides reference information for improving the quality of aquatic products from the source of aquaculture.