Diets containing Arthrospira platensis increase growth, modulate lipid metabolism, and reduce oxidative stress in pacu (Piaractus mesopotamicus) exposed to ammonia

Abstract

Ammonia is a pollutant commonly found in intensive aquaculture systems. At high levels, it can compromise animal health and cause great economic losses. Diets supplemented with additives and/or immunostimulating ingredients can improve animal health conditions and resistance to diseases. In this context, the inclusion of Arthrospira platensis (spirulina meal, SM) has shown promising results as a growth promoter, immune system stimulant, and antioxidant in fishes. The objective of this study was to evaluate the effects of replacing fish meal (FM) with SM on the growth performance, feed efficiency, biochemical parameters, and hepatic antioxidant capacity of pacu (Piaractus mesopotamicus) juveniles exposed to ammonia. The fish were fed diets with different levels of SM – 0 (SM0), 20 (SM20), 40 (SM40), and 60 g kg−1 (SM60) – replacing fish meal for 45 days, followed by 24 h of exposure to 2.5 mg L−1 ammonia. Growth performance was measured after the 45-day feeding test. The collections to evaluate the activity of alanine aminotransferase (ALT), aspartate amino transferase, catalase (CAT), superoxide dismutase (SOD), total antioxidant capacity (TAC), and malondialdehyde (MDA) were performed before and after challenge with ammonia. The results showed that fish fed SM40 and SM60 had significantly improved growth performance, weight gain % (P = 0.017), and specific growth rate % (P = 0.011) over the fish given SM0. Fish fed SM40 and SM60 had lower levels of total cholesterol (P < 0.001), triglycerides (P < 0.001), and low-density lipoprotein (P < 0.001) than the SM0 group. The plasma activity of ALT was significantly lower (P = 0.002) in fish fed SM40 or SM60 than SM0. CAT, SOD, and TAC activity were significantly higher in the SM40 and SM60 groups. The concentration of MDA increased in all treatments after exposure to ammonia compared to the level observed before the challenge. SM60 significantly mitigated the adverse effects of exposure to ammonia on the antioxidant responses of pacu. In conclusion, SM60 improved growth performance and proved effective at mitigating the adverse effects of ammonia toxicity in pacu juveniles. These effects seem to be attributable to antioxidant compounds present in spirulina, which can improve growth and mitigate ammonia-induced liver damage in pacu juveniles.