Influence of ammonia addition on the speed of formation of microbial flocs and on the performance of Pacific white shrimp, Litopenaeus vannamei, grown in a heterotrophic system
In recent years, cultivation in a heterotrophic environment has been consolidating as an alternative for the production of aquatic organisms with less environmental impact, thus, accelerating the formation of microbial flocs would make it possible to improve studies about microorganisms and, eventually, reduce production costs. The present study aimed to evaluate the influence of the addition of ammonia on the development of microbial flocs in cultivation of Litopenaeus vannamei in heterotrophic medium without water renewal. To this end, a system was set up with 15 experimental units where they were grown for 21 juvenile shrimp days in stocking density equivalent to 300 individuals/m2 with an average initial weight of 0.58 ± 0.21. Four treatments were tested: T1, adding 1.5 mg/L every 7 days; T2, addition of 3,0 mg/L of ammonia every 7 days; T3, adding 1.5 mg/L every 3 days; T4, addition of 3.0 mg/L of ammonia every 3 days and the control, where no ammonia was added. In each treatment, three repetitions were used. Sugar cane molasses was added as a carbon source in order to maintain a carbon/nitrogen ratio of approximately 20: 1. In the control treatment, carbon was only added when the ammoniacal nitrogen concentration reached 1.0 mg/L. To quantify the microbial flocs, the Imhoff cone was used daily. The water quality data were within the range considered ideal for the cultivation of L. vannamei throughout the experiment. There was no significant difference in weight gain or shrimp survival, suggesting that the concentrations of added ammonia did not harm the animals. The results of the Imhoff Cone showed a significant difference in the development of microbial flocs between the control and the different treatments, and indicate that the increase in the frequency of ammonia addition is significantly more important than the increase in ammonia concentrations.