Determination of Total Suspended Solids Concentration and Stocking Density for Juvenile Pacu (Piaractus mesopotamicus) Cultivation in a BFT System
Author: Lucas Pellegrin (Currículo Lattes)
Advisor: Dr. Luciano de Oliveira Garcia
Abstract
Piaractus mesopotamicus (pacu) is a fish species native to the La Plata Basin, with a wide geographical distribution and a broad thermal tolerance, enabling its cultivation in virtually all regions of Brazil. This species has good acceptance in the consumer market due to the quality of its flesh, which is marketed in various forms such as ribs, fillets, and whole gutted fish. Due to its hardiness, it presents desirable characteristics for intensive farming, such as tolerance to low oxygen levels and resistance to the main nitrogenous compounds generated in the system. Among existing intensive farming methods, the biofloc technology (BFT) system has shown numerous advantages, including increased stocking density without compromising water quality, improvement of the animals’ immune system, and serving as a supplementary food source, enhancing feed conversion rates and reducing feeding costs. The bioflocs present in this system have excellent nutritional composition; however, their accumulation leads to increased concentrations of total suspended solids (TSS), and excessive levels can become a limiting factor in cultivation, requiring maintenance within species-tolerated concentrations. Thus, testing the pacu’s adaptation to the BFT system and determining its tolerance to TSS becomes essential for ensuring the success of this species in such environments. Additionally, determining the optimal stocking density is a tool to ensure efficiency in cultivation systems. Four experiments (EXP) were conducted: EXP 1 - a 96-hour LC50 was performed at different TSS levels in the water (0, 1500, 3000, 4000, 5000, 6000, and 7000 mg L⁻¹) to determine the species’ safe level, with mortality recorded every 24 hours. EXP 2 - five sublethal TSS concentrations (0, 250, 500, 750, and 1000 mg L⁻¹) were tested, evaluating hematological parameters (glucose, pH, hematocrit, hemoglobin, erythrocytes, and hematimetric indices) of pacu. This experiment lasted five days, with blood samples collected at the start (day 1) and end (day 5) of the period (9 fish per treatment). EXP 3 - five TSS concentrations (0, 250, 500, 750, and 1000 mg L⁻¹) were tested to evaluate pacu’s zootechnical performance and hematological parameters over 30 days; biometric measurements were taken at the beginning (day 0) and end (day 30), and blood was collected only at the end. EXP 4 - juveniles were subjected to five stocking densities (150, 300, 450, 600, and 750 fish m⁻³), evaluating zootechnical performance and hematological changes. Biometries were performed at the start (day 0) and end (day 45), with blood collected at the end. Results demonstrated that pacu tolerates up to 5000 mg L⁻¹ of TSS for 96 hours without mortality; concentrations up to 500 mg L⁻¹ caused minor hematological alterations and can be maintained for up to five days. Concentrations up to 250 mg L⁻¹ yielded the best zootechnical performance indices. Regarding stocking density in BFT, densities of 150, 300, and 450 fish m⁻³ did not affect performance, with 450 fish m⁻³ being the most suitable, allowing the highest final biomass.