Assessment of the nitrification process in a culture of pacific white shrimp, using artificial substrate and bacterial inoculum in a biofloc technology system (BFT)

Abstract

EnglishLitopenaeus vannamei is the most cultured marine shrimp in all types of systems including the Bioflocs Technology System (BFT). Bioflocs are formed by microorganisms, among these, autotrophic bacteria are responsible for the nitrification process. This study aimed to identify and promote the development of nitrifying bacteria by adding artificial substrates and biofloc inoculum in L. vannamei culture in a BFT system. The experiment consisted of four treatments with three replics (4x3) as follows: (1) Control: clear water in which bioflocs were formed; (2) IN (10%): clear water with biofloc inoculum (10%); (3) IB: clear water with substrate (immature “bioballs”); and (4) MB: clear water with mature “bioballs” inoculum from a recirculation system. Treatments were stocked with shrimp juveniles (4.92±0.45 g) in 12 tanks with 200 L working volume at a stocking density of 200 shrimp/m³. Shrimps were fed twice a day with a commercial feed (38% CP) following a feeding table, and daily observations intake were made over the four weeks of the experiment. Biofloc and “bioballs” samples were collected to detect the growth of the population of nitrifying and heterotrophic bacteria by FISH. There was no significant difference between treatments (P>0.05) for survival, obtaining mean values greater than 88%. The IN (10%) treatment had lower concentrations of ammonia and nitrite, and nitrate concentration increased, while MB had a higher weight and biomass final, productivity, weekly weight gain and lower conversion of apparent feed for production performance results. Key words: heterotrophic bacteria; nitrifying bacteria; “bioballs”; bioflocs; FISH (Fluorescent in situ Hybridization) portuguesLitopenaeus vannamei e o camarao marinho mais cultivado em todos os tipos de sistemas, incluindo o Sistema de Tecnologia de Bioflocos (BFT). Os bioflocos sao formados por microorganismos, entre estes, bacterias autotroficas que sao responsaveis pelo processo de nitrificacao. Este estudo teve como objetivo identificar e promover o desenvolvimento de bacterias nitrificantes pela adicao de substratos artificiais e inoculo de bioflocos no cultivo de L. vannamei em sistema BFT. O experimento consistiu de quatro tratamentos com tres repeticoes (4x3), sendo: (1) Controle: agua limpa, na qual foram formados os bioflocos; (2) IN (10%): agua limpa com inoculo de bioflocos (10%); (3) BI: agua limpa com substrato (“bioballs” imaturos); e (4) BM: agua limpa com inoculo de “bioballs” maduros de um sistema de recirculacao. Para tanto, os tratamentos foram estocados com juvenis de camarao (4,92±0,45 g) em 12 tanques com 200 L de volume util com densidade de 200 camaroes/m³. Os camaroes foram alimentados duas vezes ao dia com racao comercial (38% PB) seguindo uma tabela de alimentacao, e observacoes diarias foram feitas ao longo das quatro semanas de experimento. Amostras de bioflocos e “bioballs” foram coletadas para detectar o crescimento da populacao de bacterias nitrificantes e heterotroficas por FISH. Nao houve diferenca significativa entre os tratamentos (P>0,05) para sobrevivencia, obtendo-se valores medios superiores a 88%. O tratamento com IN (10%) apresentou menores concentracoes de amonia e nitrito, e a concentracao de nitrato aumentou, enquanto o BM apresentou maior peso e biomassa final, produtividade, ganho de peso semanal e menor conversao alimentar aparente para resultados de desempenho zootecnico. Palavras-chave: Bacterias heterotroficas; bacterias nitrificantes; “bioballs”; bioflocos; FISH (Hibridizacao in Situ Fluorescente)