Evaluation of the nitrification process in the cultivation of Pacific white shrimp Litopenaeus vannamei (Boone 1931) using artificial substrate and inoculum of bacteria in a biofloc system (BFT)

Author: Nathalia Brenda Veiga dos Santos (Currículo Lattes)
Supervisor: Dr Wilson Francisco Britto Wasielesky Junior
Co-supervisor: Dr Plínio Schmidt Furtado

Abstract

The Pacific white shrimp Litopenaeus vannamei is the most widely grown marine shrimp in all types of systems, as well as in the biofloc system (Biofloc Technology System - BFT). The flakes are formed by microorganisms (bacteria, ciliates, diatoms, nematodes, etc.), feces, feed scraps, carapaces, among others, with autotrophic bacteria responsible for the nitrification process. This is a crucial step for this type of cultivation, since nitrogen compounds, in high concentrations, are toxic to shrimp. The present work aimed to promote and identify the development of nitrifying bacteria through the addition of artificial substrates and biofloc inoculum in the cultivation of L.vannamei in BFT system. The experimental design consisted of four treatments with three repetitions (4x3),these being: Control: Clear water where bioflocules were formed; IN (10%): Clear water with biofloc inoculum (10%); BI: Clear water with substrate (immature “bioballs”); BM: Clear water with inoculum of mature “bioballs” from a recirculation system. For this, juvenile shrimp (4.92 ± 0.45g) were stored in 12 tanks of 200L of useful volume, stocking density of 200 shrimp/m3. The prawns were fed twice a day with commercial feed containing 38% crude protein (Guabi- potimar/38% PB Active), following the feeding table and daily observations of food consumption, over four weeks of the experiment (28 days). Samples of bioflocules and "bioballs" were collected to detect the growth of the population of nitrifying and heterotrophic bacteria (pseudomonas spp.) through FISH (Fluorescent in situ hybridization). There was no significant difference between treatments (P> 0.05) for survival, with mean values ​​greater than 88%. The IN treatment (10%) obtained a lower concentration of ammonia and nitrite and a higher concentration of nitrate, while BM obtained a higher final weight and final biomass, productivity, weekly weight gain and less apparent feed conversion for results of zootechnical performance. Both showed a greater amount of centric diatoms compared to the other treatments. It was found that the use of inoculants at the beginning of production, whether in the form of bioflocs or substrates that already contain nitrifying bacteria, is an effective option to avoid high concentrations of nitrite and provide a better quality of water throughout the cultivation

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