Effect of Total Suspended Solids Concentration on Antioxidant Parameters and Oxidative Stress in Juvenile Piaractus mesopotamicus Reared in a Biofloc System (BFT)Author: Andressa Larré Bitencourt (Currículo Lattes)
Advisor: Dr. Luciano de Oliveira Garcia
Abstract
The biofloc system offers various advantages, such as water reuse, nutrient cycling, high stocking density, maintenance of water quality, and the potential to reduce feed usage during culture. Pacu (Piaractus mesopotamicus) is a species with favorable production characteristics and high adaptability to different farming systems, which supports its potential for cultivation in biofloc systems (BFT). However, inadequate management in BFT systems can lead to increased total suspended solids (TSS), potentially causing physiological issues in the animals. To date, the literature lacks studies indicating the optimal TSS concentration for pacu culture in relation to oxidative stress biomarkers and their impact on fish development. Therefore, the aim of the present study was to evaluate the effects of different concentrations of total suspended solids on antioxidant defense parameters and oxidative stress in juvenile pacu reared in a BFT system. Five TSS concentrations (mg/L) were tested: T1: clear water control; T2: 250; T3: 500; T4: 750; and T5: 1000, over a period of 15 days, with each treatment replicated three times (310 L tanks – 15 fish per replicate). During this period, two tissue samplings (gills, liver, and brain) were conducted, one at the beginning and one at the end of the experiment. Biochemical markers of oxidative stress were analyzed, including Glutathione S-Transferase (GST), Reduced Glutathione (GSH), Total Antioxidant Capacity against Peroxyl Radicals (ACAP), Superoxide Dismutase (SOD), and Catalase (CAT), along with lipid damage (LPO) and protein damage (PSH). Additionally, histological analyses of gills and microbial community counts in the bioflocs were performed. Results showed that at 750 and 1000 mg TSS/L, there was increased activity of the enzymes SOD, CAT, and GST, as well as higher GSH concentrations. ACAP and PSH did not show significant differences. However, LPO levels were higher in gills up to 750 mg TSS/L (p < 0.05). Histological analyses revealed greater ionocyte counts and reduced lamellar spacing (p < 0.05) in the control and 1000 mg TSS/L treatments. Microorganism abundance increased with TSS concentration (p < 0.05), particularly for bacteria and ciliates. Rotifers, nematodes, and microalgae were also observed; however, rotifers were absent at 500 mg TSS/L, nematodes at 1000 mg TSS/L, and microalgae were only observed at the beginning and end of the experiment in the 1000 mg TSS/L treatment, and only at the end in the other treatments (p < 0.05). Based on the results, it is concluded that pacu cultivation in biofloc systems can be carried out up to 500 mg TSS/L. Above 750 mg TSS/L, gill damage and alterations in the antioxidant system begin to occur.