Formation of microbial flocs in cultivation of pink shrimp Farfantepenaeus paulensis and white shrimp Litopenaeus vannamei
The objective of the present work was to verify if the formation of microbial flocs occurs differently in intensive cultivations of Farfantepenaeus paulensis and Litopenaeus vannamei in heterotrophic systems without water exchange (ZEAH). For this, we tried to characterize the dynamics of the microbial community, its interaction with nutrients in the culture system and to verify if the microbial flake serves as a food supplement for these two species. The experiment consisted of three treatments, with four repetitions each: 1) SC treatment - without shrimp; 2) FP treatment - with shrimp F. paulensis and 3) LV treatment - with shrimp L. vannamei. All treatments received daily organic fertilization in order to induce the formation of the microbial flake, maintaining a C: N ratio of 20: 1.Tanks of 300 L (200 L of useful volume) were populated with juveniles of L. vannamei and F. paulensis (0.06 g and 0.07 g respectively) at a density of 300 shrimp / m2. The dissolved nutrients, weight of seston, chlorophyll a and microbial community were analyzed by collecting water from each tank every two days in the first week and then every three days until the end of the study period (35 days). The water quality parameters were within the recommended levels for the cultivation of peneid shrimp, not compromising their growth and survival. The presence of different species of shrimp seems to influence the formation of microbial flocs, evidenced by the higher values of suspended material in the LV treatment compared to the FP and SC treatments. Besides that,there were also different concentrations of nutrients (mainly phosphate) and different N: P ratios in tanks with LV, FP and those without shrimp. A close relationship was observed between the amount of aggregates and the presence of adhered coccoid bacteria. These were dominant in LV, where the average values of the N: P ratio (5.8: 1) were higher than in the other treatments. This indicates that a higher N: P ratio should favor mucus-producing coccoid bacteria and that they participate in the formation of microbial flocs. Weight gain and final weight in LV was twice as high as FP. The apparent Food Conversion Factor (FCA) in LV was lower than that observed in crops in clear water, which allows us to infer that the microbiota of the aggregates served as supplementary food for L. vannamei,the same is not true for F. paulensis x, probably due to their high nutritional requirements or their different eating habits from L. vannamei, which seems to be better adapted to the consumption of aggregates.