Effect of the addition of Thalassiosira weissflogii and silicate on the cultivation of white shrimp Litopenaeus vannamei in a super intensive system with bioflocs
Author: Shayene Agatha Marzarotto (Currículo Lattes)
Supervisor: Dra Clarisse Odebrecht
Co-supervisor: Dr Wilson Francisco Britto Wasielesky Junior
Abstract
Some diatoms are important in aquaculture due to their nutritional qualities and contribution to the formation of microbial flocs. In order to evaluate the growth and maintenance of the population of the diatom Thalassiosira weissflogii in a biofloc cultivation system and its effect on the performance of the shrimp Litopenaeus vannamei, an experiment was carried out (six treatments, three repetitions) with stocking density of 300 shrimp m2: The treatments were: Control (without diatoms), T 2.5 (inoculation 2.5x104 cells / mL of T. weissflogii); T 5 (inoculation 5.0 x 10 4 cells / ml of T. weissflogii); T Si (addition of sodium silicate); T 2.5 Si (2.5 x 10 4 cells / mL inoculation and addition of sodium silicate); T 5 Si (inoculation 5.0 x104 cells / mL and addition of sodium silicate),with diatomaceous inoculations and silicate additions every four and seven days, respectively. The physical and chemical parameters of the water were monitored daily and, every three days, the concentration of ammonia, nitrite, alkalinity, nitrate, silicate, chlorophyll a and microorganisms. The prawns (average initial weight of 0.51 ± 0.41 g) were fed three times a day, in trays with commercial feed 38% PB, at the rate of 8% of the initial biomass. After 30 days, performance was assessed for survival, weight gain and specific growth rates and apparent feed conversion. The diatoms T. weissflogii remained in high density for about 17 days, coinciding with a high concentration of nitrite, regardless of the silicate content. The high concentration of nitrite probably negatively affected the growth of L. vannamei.Cyanobacteria have dominated crops since the beginning, with the presence of amoebae attacked with phyllopods, and in a smaller number of streaked diatoms. Shrimp survival was statistically higher (α = 0.05) in treatment 2.5 (68%), but the specific growth rate and weight gain were similar between treatments; the apparent feed conversion rate (TCCA) was better in the control, which differed significantly from T 5 and T Si. Silicate seems to have negatively influenced shrimp survival and TCAA, but not on the growth and maintenance of T. weissflogii in bioflocs. The presence of T. weissflogii did not significantly influence the zootechnical performance of L. vannamei in the present experiment