Nitrification Process in Different Intensive Systems for the Production of the Shrimp Litopenaeus vannamei
Author: Fabiane da Paz Serra (Currículo Lattes)
Advisor: Prof. Dr. Paulo Cesar Abreu (in memoriam)
Abstract
One of the main challenges in aquaculture systems is the waste generated during production, which is one of the primary causes of the environmental impact of the activity—an issue that tends to intensify as production becomes more intensive. In this context, nitrogen (N) control is essential for the success of production, especially ammonia and nitrite, which are the most toxic nitrogenous compounds to farmed organisms. To address this, research has been conducted to optimize intensive and super-intensive production systems. Microorganism-based systems have emerged as promising alternatives for production intensification, contributing to the sustainability and biosecurity of aquaculture activities. Among these, biofloc and biofilm-based systems stand out. In both systems, proper management is necessary to promote the proliferation and establishment of nitrifying bacteria, which are primarily responsible for the biological removal of toxic nitrogen. For this purpose, understanding the nitrogen dynamics and bacterial communities in different production systems is crucial. Based on this, the thesis was divided into three chapters focused on nitrogen dynamics and nitrifying bacteria. In the first chapter, we evaluated nitrogen availability and substrates to improve the nitrification process during system maturation and shrimp production in three different systems: clear water, biofloc, and biofilm. The results demonstrated that prior inorganic fertilization, combined with the presence of substrates—particularly artificial substrates for biofilm formation—led to greater efficiency in the nitrification process and higher final shrimp biomass. In the second and third chapters, we used the FISH technique (Fluorescence In Situ Hybridization) to assess the composition and quantify nitrifying bacteria, thereby supporting the findings of the first chapter, which was based solely on nitrogen dynamics. In the second chapter, we evaluated the factors influencing the establishment of nitrifying bacteria during the startup phase of different production systems. Quantification of nitrifying bacteria showed that excessive increases in ammonia and nitrite levels were directly related to the absence or low density of nitrifying bacteria, due to water exchanges, lack of substrate, and addition of organic carbon during the system's initialization. In the third chapter, we compared nitrogen dynamics and nitrifying bacterial communities in mature biofloc and biofilm systems. In this case, both strategies proved effective in maintaining ammonia and nitrite concentrations at safe levels for shrimp. However, nitrogen dynamics, along with FISH analyses, revealed that the efficiency of the nitrification process was associated with the density of nitrifying bacteria, which was influenced by management practices applied during both system maturation and production phases.