Piaractus mesopotamicus exposed to different total suspended solids in a biofloc technologic system: short-term effects on oxidative stress and morphology

This study aimed to evaluate the short-term effects of different concentrations of total suspended solids on the antioxidant defense and oxidative stress parameters in juveniles pacu in a biofloc technology system. For this study, five total suspended solid concentrations (mg TSS L-1) were tested (T1: clear water control; T2: 250; T3: 500, T4: 750, and T5: 1000), each concentration (n = 45) was tested in triplicate (n = 15) for 15 days. During this period, gills, liver, and brain tissue were collected twice, at the beginning and the end of the experiment. Biochemical parameters of oxidative stress were evaluated: Glutathione-S-Transferase (GST), Reduced Glutathione (GSH), Total Antioxidant Capacity against Peroxyl Radicals (ACAP), Superoxide Dismutase (SOD), Catalase (CAT), Lipid Peroxidation (LPO), and Protein Damage (Protein Thiols). In addition, histological analyses of the gills tissue were performed. According to the analyses, our findings show higher activity of the SOD, CAT, GST enzyme, and GSH concentrations at 750 and 1000 mg TSS L-1. Regarding ACAP and PSH, there were no significant differences. However, LPO levels were higher up to the concentration of 750 mg TSS L-1 in the gills. Histological analyses showed higher ionocyte counts and thinner lamellae thickness in the treatment at 1000 mg TSS L-1. Therefore, according to the results, we conclude that pacu can be exposed in the biofloc system up to 500 mg TSS L-1, due to the damage to the gills and changes in the antioxidant system when the concentration is from 750 mg TSS L-1.